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Learning Objectives

After studying this chapter, you should be able to:

• Discuss the historical development of our scientific understanding of the greenhouse effect and cli- mate change, especially the connection between atmospheric concentrations of greenhouse gases and temperature.

• Review some of the major impacts of climate change that are predicted to occur, or are already occur- ring, including more extreme weather, changes in water supply, impacts to human health, extinction of animal species, and rising sea levels.

• Describe how climate change might impact agricultural production and food supply in various regions of the world.

• Explain the importance of the stratospheric ozone layer to life on Earth and discuss the ways in which the use of chlorofluorocarbons (CFCs) resulted in ozone depletion and the emergence of an ozone hole.

• Discuss the relationship between carbon dioxide emissions and ocean acidification and how changes to ocean chemistry could impact the productivity and biodiversity of the seas.

Global Climate Change and Ozone Depletion 7

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Pre-Test

1. the greenhouse effect is a natural phenomenon. a. true b. False 2. Major scientific assessments have determined that natural causes could be responsible

for much of the observed changes to climate in recent decades. a. true b. False 3. Food insecurity and rising food prices were major factors in the unrest and uprisings

known as the Arab Spring. a. true b. False 4. the ozone layer that protects life on Earth is located primarily in what region of the

atmosphere? a. troposphere b. Mesosphere c. Stratosphere d. Ionosphere 5. Scientific research has revealed that excess carbon dioxide emissions are making the

oceans less acidic. a. true b. False

Answers 1. a. true. the answer can be found in section 7.1. 2. b. False. the answer can be found in section 7.2. 3. a. true. the answer can be found in section 7.3. 4. c. Stratosphere. the answer can be found in section 7.4. 5. b. False. the answer can be found in section 7.5.

Introduction In 982, Erik the Red left his homeland with a small band of followers and sailed west from Iceland to establish a colony on Greenland, which was previously uninhabited by Europeans. the Vikings farmed, raised sheep, and traveled even farther north to hunt seals, walrus, and whales. the settlement flourished for about 500 years, eventually growing to 4,000 inhabit- ants. Eventually, all the colonists died out and the abandoned farms and weathered tomb- stones stood out against the arctic sky. Although there are many reasons why this tragedy occurred, experts agree that climate change played a part. From about 1450 to 1850, in a period called the “Little Ice Age,” the northern Hemisphere became unusually cold by histori- cal standards. In the Arctic colonies, this cooling trend led to crop failure and starvation, and the settlers were unable to survive.

Climate change is not a new thing, and global temperatures have gone up and down through- out the history of the Earth. However, recent warming of the planet has generated concern

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IntRoDuCtIon

among scientists and others for at least two reasons. First, whereas past climate changes were caused by natural factors, the current warming trend is primarily the result of human activi- ties. Second, if not addressed soon, climate change has the potential to disrupt agriculture, water supply, weather patterns, and other conditions essential for our survival. As such it’s important to gain a solid understanding of what climate change is and the science behind it.

Climate change is also among the most controversial of environmental issues, and in recent years the issue has become highly politicized. In studying climate change it is important to try to keep separate the scientific study of the issue and the political implications that might fol- low from that research. the vast majority of scientists studying climate change bring no par- ticular political agenda to their work. However, because that research is increasingly pointing to the reality of climate change and a major human role in causing that change, it is sometimes dismissed as being motivated by a political agenda.

In order to keep these issues in perspective, it is helpful to consider the difference between arguments that are based on positive claims, or statements about what we know, and argu- ments based on normative claims, statements about what we value (Dessler and Parson, 2006). When a climate scientist makes a claim that atmospheric carbon dioxide concentra- tions are rising and that average global temperatures are increasing, that is a positive claim, a statement about the way things are. When a politician makes an argument that we should increase taxes on gasoline to reduce carbon dioxide emissions, that is a normative statement, an argument for the way things should be (at least in the view of that politician). Scientific research has political implications, but recall from the earlier discussion of the scientific method that this research is guided by a set of principles that keep it focused on understand- ing the way the world is. How politicians and others make use of that research to argue for the way the world should be is a separate issue from the validity and integrity of the original scientific research.

Before we begin the readings on climate change, this chapter will open with a series of ques- tions and answers, or Frequently Asked Questions (FAQs), that will lay the foundation for your understanding of this issue. the first reading will then introduce you to the history of climate change science in order to help illustrate how we came to understand what we now know about this issue. this is followed by a comprehensive review of the causes and conse- quences of climate change, a reading that will tie together and test your knowledge of the information presented in the opening FAQ section. Section 7.3 addresses one of the most wor- risome aspects of climate change, its potential impact on world food production and sup- plies. Section 7.4 shifts gears a little and introduces the issue of stratospheric ozone deple- tion. While ozone depletion and climate change are sometimes confused and thought to be the same problem, these are largely separate and unrelated issues. the final section presents a case history of how carbon dioxide emissions and global warming are impacting the world’s oceans in potentially devastating ways. Whereas this chapter is primarily focused on the global warming problem, the following chapter will introduce some possible solutions in the form of alternative energy sources. Since carbon dioxide emissions from fossil fuel combus- tions are the single greatest contributor to human-caused climate change, alternative energy sources represent one of the most important responses to this issue.

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The Basics of Climate Change—Frequently Asked Questions 1. What factors determine the Earth’s climate? our climate system is powered by solar radiation from the sun and is determined by the energy balance of incoming and outgoing energy (see Figure 7.1). About one-third of incoming, short- wave solar radiation is reflected by clouds or light surfaces on the Earth (like ice and snow) and bounced back to space. Much more of this shortwave radiation is absorbed by the Earth’s surface and then given off or re-radiated as heat energy. If you’ve ever stood barefoot on a dark surface on a sunny summer day, you’ve experienced this firsthand. Greenhouse gases such as water vapor and carbon dioxide are present naturally in the atmosphere, and they absorb and trap some of this outgoing radiation and help keep the Earth’s surface relatively warm. Learn more about this here:

• https://www.ipcc.unibe.ch/publications/wg1-ar4/faq/wg1_faq-1.1.html

Figure 7.1: Earth’s energy balance

the sun emits shortwave solar radiation onto the Earth’s surface. Some of this radiation is reflected back into space by clouds and light surfaces such as snow or ice on mountains. Most of the shortwave radiation is absorbed by the Earth’s surface and then re-radiated or released back as infrared or heat energy. Some of this heat energy is then absorbed and re-radiated back toward the Earth’s surface by greenhouse gases like carbon dioxide and water vapor.

2. What is the greenhouse effect? the two most abundant gases in the atmosphere are nitrogen and oxygen, together account- ing for roughly 99 percent of the total. these gases play almost no role in trapping or absorb- ing the outgoing heat energy coming from the Earth’s surface. Instead, other gases present in extremely small quantities in the Earth’s atmosphere absorb and re-radiate outgoing heat or longwave radiation. these gases—including water vapor, carbon dioxide, methane, and nitrous oxide—act like a blanket helping to hold heat energy close to the Earth’s surface. these gases could also be thought of as windows in a greenhouse or car, allowing sunlight to pass

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The Basics of Climate Change—Frequently Asked Questions (continued)

through the atmosphere but trapping the heat that tries to escape (see Figure 7.2). Although they only make up a fraction of a percent of the composition of the atmosphere, these green- house gases are responsible for the greenhouse effect and essentially for life as we know it. It’s estimated that without greenhouse gases, the average temperature on Earth would be about 0 degrees Fahrenheit (F). Instead, the average surface temperature globally is 59 degrees F. Learn more about this here:

• https://www.ipcc.unibe.ch/publications/wg1-ar4/faq/wg1_faq-1.3.html • http://www2.sunysuffolk.edu/mandias/global_warming/greenhouse_gases.html

3. How are the greenhouse effect, global warming, and global climate change different?

the greenhouse effect is a natural phenomenon without which we might not be here. When we talk of global warming we are really referring to an enhanced greenhouse effect caused by human emissions of greenhouse gases like carbon dioxide. these human emissions, for example from burning fossil fuels, are increasing the concentration of greenhouse gases in the atmosphere and contributing to global warming. While essentially the same thing, most sci- entists prefer to use the term global climate change since warming of the Earth is also altering precipitation patterns and other factors related to climate. Learn more about this here:

• http://www.bis.gov.uk/go-science/climatescience

4. What is the difference or the relationship between climate and weather? the old saying is that “climate is what you expect, weather is what you get.” Climate can thus be explained as the average weather in a particular place over many years. Global warming or global climate change does not mean that we will no longer have cold weather. Instead, it means that on average we should expect to see less cold weather and an increase in warmer temperatures in most parts of the world, a prediction that is borne out definitively by the data. Learn more about this here:

• https://www.ipcc.unibe.ch/publications/wg1-ar4/faq/wg1_faq-1.2.html • http://www.eo.ucar.edu/basics/

5. How do human activities contribute to climate change, and are they more or less important than natural factors?

While we know that we are currently experiencing a period of warming, how can we be certain that this is a result mainly of human activities? Scientists call this a question of attribution; to what can we attribute the observed warming? Scientists start by looking at all of the differ- ent possible causes of warming and then examine whether any of them provide a plausible explanation for what we are seeing. For example, throughout the history of the planet factors like tectonic activity, volcanic eruptions, variations in the Earth’s orbit, changes in solar radia- tion, and internal variation in the Earth’s climate system (e.g., the El niño phenomenon) have contributed to climate change. However, when scientists examine all of these factors, none of them alone or in combination comes close to explaining the actual warming we are currently seeing. In contrast, the steady increase in greenhouse gas concentrations in the atmosphere

(continued)

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The Basics of Climate Change—Frequently Asked Questions (continued)

due to human activities like fossil fuel burning does explain the observed warming. therefore, climate scientists are confident in attributing current climate change largely to human factors. Learn more about this here:

• https://www.ipcc.unibe.ch/publications/wg1-ar4/faq/wg1_faq-2.1.html • http://www2.sunysuffolk.edu/mandias/global_warming/natural_causes_climate

_change.html • http://www.c2es.org/science-impacts/basics/faqs/climate-science#Causes

6. How are temperatures changing, and is it true that global warming has stopped or paused?

Measurements of surface temperatures from around the planet going back to about 1850 show a clear trend of increasing temperature over time. Furthermore, average temperatures have generally been rising at an increasing rate. However, recent claims have been made that global warming has paused and that the planet has stopped warming since the late-1990s. Such claims are a good example of how scientific data can be misrepresented to make mislead- ing and false claims. In reality, a number of factors are currently at work. First, persistent La niña conditions and an increase in volcanic activity (which puts particles into the atmosphere that block incoming sunlight) have slowed the rate of temperature increases in recent years, but 20 of the warmest years on record have occurred in the last 25 years. Second, the oceans have been warming far faster than land areas, suggesting that they are, at least temporarily, storing much of the increased heat caused by higher levels of greenhouse gases in the atmo- sphere. third, some climate skeptics have been using graphs showing trends in global tem- peratures since 1998, suggesting that temperatures have flattened out. However, 1998 was tied for the second-warmest year on record, so using that year as your starting date paints a misleading picture of the long-term trend. Learn more about this here:

• http://www.youtube.com/watch?v=r_qdEtSYcDM • http://www2.sunysuffolk.edu/mandias/global_warming/global_cooling.html • http://www2.sunysuffolk.edu/mandias/global_warming/modern_day_climate_change

.html • https://www.ipcc.unibe.ch/publications/wg1-ar4/faq/wg1_faq-3.1.html • http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004030/

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The Basics of Climate Change—Frequently Asked Questions (continued)

Figure 7.2: Greenhouse effect

the greenhouse effect derives its name from the fact that the atmosphere acts something like a greenhouse. the sun’s rays can pass through the atmosphere, which acts like glass in a greenhouse, and strike the Earth’s surface where they are converted to infrared or heat energy. However, just like the glass in a greenhouse, the various greenhouse gases help to trap some of that heat inside the structure. Adding more greenhouse gases to the atmosphere is like thickening the glass in a greenhouse, trapping more heat in and increasing the temperature.

7. Is global climate change an ethical issue? Won’t “solving” the global warming problem ruin our economy?

While the debate over climate change might appear to be mainly a scientific one, it is also one of the most important ethical issues of our time. Because climate change can lead to rising sea levels, changes in precipitation patterns, and disruptions in water supply, it could have serious impacts on our ability to grow enough food to feed ourselves. While relatively wealthier coun- tries like the united States have the resources and technology to adapt to some of these changes,

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The Basics of Climate Change—Frequently Asked Questions (continued)

poorer countries are far more vulnerable and less able to adapt. Since the vast majority of the greenhouse gas emissions that are causing climate change have come from wealthy coun- tries like the united States, there is a clear ethical problem in this situation. Likewise, today’s population changing the climate for future generations poses an enormous ethical dilemma. In terms of economic impact, many of the most immediate approaches to reducing green- house gas emissions actually involve reducing energy use and saving money. Also, renewable energy sources like wind and the sun are domestic forms of energy whose development could help spur economic activity in the united States. Much of the opposition to addressing climate change has come from fossil fuel industries (especially coal and oil) that stand to see their profits reduced dramatically if any serious efforts are made to address global climate change. Learn more about this here:

• http://www.ucsusa.org/global_warming/solutions/reduce-emissions/climate-2030-blue print.html

8. What are the major impacts of global climate change? What does the future hold and what chance do we have to adapt to changing conditions?

While not all of the impacts of global climate change will be entirely negative, we are already witnessing some of the consequences of a warming world. Scientists studying the impacts of climate change typically categorize these into water supply and quality, ecosystem changes, food production, coastal flooding and erosion, and human health impacts. For example, cli- mate change is contributing to shifts in precipitation patterns and thus in water availability. While some areas get more water, others get less, and shifting human settlements and food production systems to where water is available is not really feasible on any sort of large scale. Ecosystem impacts include shifting ranges for wildlife and plants and the possible extinc- tion of as many as one-third of all species on the planet. More erratic weather and shifting precipitation patterns could disrupt food production in many areas, especially for some of the poorest and most vulnerable people on the planet (see section 7.3). Sea level rise from warmer oceans and melting ice is already resulting in increased floods and coastal erosion in low-lying areas home to tens of millions of people around the world. Finally, negative impacts on human health include increased heat stress, increased malnutrition from crop failures, and the spread of diseases into new areas. While adaptation is possible in some cases, the ability to adapt is often a function of wealth and technological capacity. It is the poorest and most vulnerable populations on the planet who are least responsible for global climate change but who will feel the worst consequences of this phenomenon. Learn more about this here:

• http://www2.sunysuffolk.edu/mandias/global_warming/impact_climate_change.html • http://changingclimates.colostate.edu/docs/BellCurveAveragesExtremes.pdf • http://www.climatehotmap.org • http://extremeicesurvey.org

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SECtIon 7.1A BRIEF HIStoRY oF tHE CLIMAtE CHAnGE DEBAtE

7.1 A Brief History of the Climate Change Debate Most people would assume that concern over global warming or global climate change was a fairly recent phenomenon. However, as this brief article by Stephan Harding of Schumacher Col- lege in England points out, scientists as far back as the 1820s took note of possible links between human activities and the climate system.

These scientists developed a basic understanding of what is known as the greenhouse effect, which will be described in more detail in the next section. At a basic level, the greenhouse effect involves certain gases that are naturally present in the atmosphere that trap infrared or heat energy as it escapes from the Earth’s surface. In essence, these gases act like the glass panes on a greenhouse. They allow sunlight in but block heat from escaping, which results in warmer temperatures. The greenhouse effect is a natural phenomenon. In fact, without it, the Earth’s average surface temperature would be a frigid 0 degrees Fahrenheit (°F) rather than its actual average temperature of around 59 °F.

What got the attention of the scientists discussed in this article were the increased concentrations of greenhouse gases in the atmosphere due to human activities. In particular, the burning of fossil fuels such as coal and oil, which releases carbon dioxide (CO2), the most common of the green- house gases after water vapor. The scientists hypothesized that adding more CO2 to the atmo- sphere could increase global temperatures and change climate. It was not until decades later, however, that scientific instrumentation advanced enough to determine that, in fact, atmospheric CO2 concentrations were increasing and that this was due almost entirely to human activities.

Today it is widely acknowledged that global average temperatures have increased since the Industrial Revolution and the widespread use of fossil fuels. However, scientists do not accept the simple presence of a correlation (higher CO2 concentrations and higher temperatures) as proof of a cause-effect relationship. Instead, other possible causes of increased temperatures (such as variations in solar energy output from the sun) also must be considered. Scientists refer to this as the issue of attribution, or to what can the observed temperature increases be attributed. Although there is still some debate over the attribution issue, there is a solid consensus that increased CO2 concentrations, due mainly to fossil fuel combustion, are primarily responsible for the observed increase in global temperatures in recent decades.

This reading helps us understand the historical basis for our current understanding of climate change. The next section will explore in more detail the actual causes and consequences of cli- mate change. Sections 7.3 and 7.5 will examine two of the most troubling impacts of our green- house gas emissions and climate change: food supply disruptions and changes to the health of our oceans.

By Stephan Harding our understanding of climate change began with intense debates amongst 19th century sci- entists about whether northern Europe had been covered by ice thousands of years ago. In the 1820s Jean Baptiste Joseph Fourier [a French mathematician and physicist] discovered that “greenhouse gasses” trap heat radiated from the Earth’s surface after it has absorbed energy from the sun. In 1859 John tyndall [a British physicist] suggested that ice ages were caused by a decrease in the amount of atmospheric carbon dioxide. In 1896 Svente Arrhenius [a Swedish physicist and chemist] showed that doubling the carbon dioxide content of the air would gradually raise global temperatures by 5–6 °C—a remarkably prescient result that was virtually ignored by scientists obsessed with explaining the ice ages.

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SECtIon 7.1A BRIEF HIStoRY oF tHE CLIMAtE CHAnGE DEBAtE

the idea of global warming languished until 1938, when Guy S Callender [a British engi- neer and inventor] suggested that the warming trend revealed in the 19th century had been caused by a 10% increase in atmospheric carbon dioxide from the burning of fossil fuels. At this point scientists were not alarmed, as they were confident that most of the carbon dioxide emitted by humans had dissolved safely in the oceans. However, this notion was dispelled in 1957 by Hans Suess [an Austrian physical chemist and nuclear physicist] and Roger Revelle [an American oceanographer], who discovered a complex chemical buffering system which prevents sea water from holding on to much atmospheric carbon dioxide.

the possibility that humans could contribute to global warming was now being taken seri- ously by scientists, and by the early 1960s some had begun to raise the spectre of severe climate change within a century. they had started to collect evidence to test the idea that global temperatures were increasing alongside greenhouse gas emissions, and to construct mathematical models to predict future climates.

In 1958 Charles Keeling [an American geochemist and oceanographer] began long-term mea- surements of atmospheric carbon dioxide at the Mauna Loa observatory in Hawaii. Looked at now, the figures show an indisputable annual increase, with roughly 30% more of the gas relative to pre-industrial levels in today’s atmosphere—higher than at any time in the last 700,000 years. temperature readings reveal an average warming of 0.5–0.6 °C over the last 150 years.

Figure 7.3: Atmospheric CO2 concentration at Mauna Loa

Graph shows the mean Co2 concentration at the Mauna Loa observatory from 1959 to 2012.

Based on data from U.S. Department of Commerce, National Oceanic & Atmospheric Administration. Retrieved from ftp://ftp.cmdl .noaa.gov/ccg/co2/trends/co2_annmean_mlo.txt.

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SECtIon 7.1A BRIEF HIStoRY oF tHE CLIMAtE CHAnGE DEBAtE

Climate change sceptics have pointed out that these records could have been due to creep- ing urbanisation around weather stations, but it is now widely accepted that this ‘urban heat island effect’ is relatively unimportant and that it doesn’t explain why most of the warming has been detected far away from cities, over the oceans and the poles.

The Case for Global Warming Since the 1960s, evidence of global warming has continued to accumulate. In 1998 Michael Mann [professor and director of the Earth System Science Center at Penn State university] and colleagues published a detailed analysis of global average temperature over the last mil- lennium known as the “hockey stick graph”, revealing a rapid temperature increase since the industrial revolution. Despite concerted efforts to find fault with Mann’s methodology, his basic result is now accepted as sound. then, in 2005, just as the Kyoto Protocol for limiting greenhouse gas emissions was ratified, James Hansen [head of the nASA Goddard Institute for Space Studies] and his team detected a dramatic warming of the world’s oceans—just as expected in a warming world.

there is now little doubt that the temperature increase over the last 150 years is real, but debate still surrounds the causes. We know that the warming during the first half of the last century was almost certainly due to a more vigorous output of solar energy, and some sci- entists have suggested that increased solar activity and greater volcanic emissions of car- bon dioxide are responsible for all of the increase. But others point out that during the last 50 years the sun and volcanoes have been less active and could not have caused the warming over that period.

By 2005 a widespread scientific consensus had emerged that serious, large-scale disruption could occur around 2050, once average global temperature increase exceeds about 2 °C, lead- ing to abrupt and irreversible changes. these include the melting of a large proportion of the Greenland ice cap (now already under way), the reconfiguration of the global oceanic circula- tion, the disappearance of the Amazon forest, the emission of methane from permafrost and undersea methane hydrates, and the release of carbon dioxide from soils.

this new theory of “abrupt climate change” has overturned earlier predictions of gradual change and has prompted some scientists to warn that unmitigated climate change could lead to the complete collapse of civilisation. Fears have been fuelled by the possibility that smoke, hazes and particles from burning vegetation and fossil fuels could be masking global warming by bouncing solar energy back to space. this “global dimming” effect is diminishing as we clean up air pollution. As a result global average temperature could rise by as much as 10 degrees Cel- sius [approximately 18 °F] by the close of the century—a catastrophic increase.

A more conservative assessment by the Intergovernmental Panel on Climate Change (IPCC) in 2001 indicated that with unabated carbon emissions, global temperature could rise gradually to

Consider This What tools and techniques might climate scientists use to predict how Earth’s cli- mate could change over time in response to increased carbon dioxide levels? How might a better understanding of past cli- mate conditions help them better predict the future?

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SECtIon 7.2Global Climate ChanGe—Causes and ConsequenCes

around 5.8 °C [roughly 10 °F] by 2100. An increase of this nature would still threaten the lives of millions of people, particularly in the global south, due to sea level rise and extreme weather events.

Although some people still deny that climate change is a problem we can do something about, last year the uK government indicated that it was on board. the Stern Review showed that without immediate and relatively inexpensive action, climate change would lead to severe and permanent global economic depression by 2050. there is now a strong scientific and economic consensus about the severity of the climate crisis.

Adapted from Harding, S. (2007, January 8). The Long Road to Enlightenment. the Guardian. Retrieved from http://www.guardian.co.uk/environment/2007/jan/08/climatechange.climatechangeenvironment/print Copy- right Guardian News & Media Ltd 2013. Used by permission.

7.2 Global Climate Change—Causes and Consequences The majority of scientific research conducted on environmental issues like climate change is often highly specific to a particular aspect of the problem. For example, one group of scientists might study whether soot particles from burning coal block incoming sunlight or absorb it, and another group might look at how oceans respond to higher concentrations of CO2 in the atmo- sphere. Due to the sheer scale of the global climate system, understanding how all the pieces fit together requires the effort of larger assessment or research bodies. The reading below from the Pew Center on Global Climate Change presents some of the summary findings of two such bod- ies, the Intergovernmental Panel on Climate Change (IPCC) and the U.S. Global Change Research Program (USGCRP). The work of the IPCC is sponsored by the United Nations and is focused on reviewing, assessing, and synthesizing current scientific research on climate change. The USGCRP coordinates federal research on climate change in the United States.

The big picture summaries provided by the IPCC and the USGCRP suggest that the Earth is warming and that human activities are very likely (over 95 percent confidence) the primary cause of this warming. While these groups acknowledge that our climate system is subject to natural variations, they conclude that recent climate change is too rapid and outside the range of what we could expect from just natural causes. Furthermore, the article argues that none of the known causes of natural climate change are able to explain the observed changes of recent decades. In contrast, the well-understood connection between greenhouse gas concentrations and temperature, known as the greenhouse effect, can explain these changes.

In this case, though, we are experiencing an enhanced greenhouse effect where human activities are pushing greenhouse gas concentrations to levels not seen for hundreds of thousands of years. The main greenhouse gases of concern are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Atmospheric concentrations of CO2 are now over 40 percent higher than what they were before the Industrial Revolution began, and corresponding increases for CH4 and N2O are 148 percent and 18 percent, respectively. Because these gases have the ability to absorb and re-radiate infrared energy from the Earth’s surface, research indicates that higher concentra- tions would certainly provide one plausible explanation for observed increases in temperature.

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SECtIon 7.2Global Climate ChanGe—Causes and ConsequenCes

In addition to providing an overview and explanation of the possible causes of global climate change, the following article examines some possible consequences. It makes clear that most scientists studying this issue prefer the term “global climate change” over “global warming” because it is not just global temperatures but also broader climatic factors such as rain and wind patterns that are being affected. Predicting precise impacts of climate change on small spatial scales is fraught with difficulties, but some expected impacts of climate change are already being observed. For example, the next section (7.3) will focus on climate change impacts on agricul- ture. The scientific assessment work summarized in this section represents the consensus view of well over 95 percent of the world’s leading climate experts and is probably as close as one could come to anything like a scientific consensus on the issue.

By The Center for Climate and Energy Solutions A study released by the u.S. national Academy of Sciences in 2010 said, “Climate change is occurring, is caused largely by human activities, and poses significant risks for—and in many cases is already affecting—a broad range of human and natural systems.” the climate will continue to change for decades as a result of past human activities, but scientists say that the worst impacts can still be avoided if action is taken soon.

Global Temperatures: The Earth Is Warming Global average temperature data based on reliable thermometer measurements are available back to 1880. over the last century, the global average temperatures rose by almost 1.5 °F, and the Arctic warmed about twice as much.

Based on data from the u.S. national Cli- matic Data Center, the 27 warmest years since 1880 all occurred in the 30 years from 1980 to 2009; the warmest year was 2005 followed closely by 1998.

over the past 50 years, the data on extreme temperatures have shown simi- lar trends of rising temperatures: cold days, cold nights, and frosts occurred less frequently over time, while hot days, hot nights, and heat waves occurred more frequently.

Warming has not been limited to the earth’s surface; the oceans have absorbed most of the heat that has been added to the climate system, resulting in a persistent rise in ocean tem- peratures. over time, the heat already absorbed by the ocean will be released back to the atmosphere, causing an additional 1 °F of surface warming; in other words, some additional atmospheric warming is already “in the pipeline.”

Consider This note that in discussing climate change, scientists are measuring global average temperature. How does climate differ from weather? How are they related? Does a par- ticularly hot or cold spell in one location tell us much about climate change? What if we observe large increases in hot or cold spells over a much larger geographic area?

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SECtIon 7.2Global Climate ChanGe—Causes and ConsequenCes

Greenhouse Gases: Making the Connection Although global temperatures have varied naturally over thousands of years, scientists study- ing the climate system say that natural variability alone cannot account for the rapid rise in global temperatures during recent decades. Human activities cause climate change by adding carbon dioxide (Co2) and certain other heat-trapping gases to the atmosphere. When sunlight reaches the earth’s surface, it can be reflected (especially by bright surfaces like snow) or absorbed (especially by dark surfaces like open water or tree tops). Absorbed sunlight warms the surface and is released back into the atmosphere as heat. Certain gases trap this heat in the atmosphere, warming the Earth’s surface. this warming is known as the greenhouse effect and the heat-trapping gases are known as greenhouse gases (GHGs).

Co2, methane (CH4), and nitrous oxide (n2o) are GHGs that both occur naturally and also are released by human activities. Before human activities began to emit these gases in recent centuries, their natural occurrence resulted in a natural greenhouse effect. Without the natural greenhouse effect, the earth’s surface would be nearly 60 °F colder on average, well below freezing. However, humans are currently adding to the naturally occurring GHGs in the atmosphere, causing more warming than occurs naturally. Scientists often call this

human-magnified greenhouse effect the “enhanced greenhouse effect.”

Evidence from many scientific studies confirms that the enhanced greenhouse effect is occurring. For example, scientists working at nASA’s Goddard Institute for Space Studies found more energy from the sun is being absorbed than is being emitted back to space. this energy imbal- ance is direct evidence for the enhanced greenhouse effect.

Greenhouse Gas Levels Rising In 2009, the u.S. Global Change Research Program (uSGCRP) released the most up-to-date and comprehensive report currently available about the impacts of climate change in the united States. the report says that average global concen- trations of the three main greenhouse gases—Co2, CH4, and n2o—are rising because of human activities. Since pre- industrial times, Co2 has increased by 40 percent, CH4 by 148 percent, and n2o by 18 percent.

Co2 is the principal gas contributing to the enhanced greenhouse effect. Many human activities produce Co2; the burn- ing of coal, oil, and natural gas account

© Craig Hanson/iStock/Thinkstock

Three main greenhouse gases—CO2, CH4, and N2O—are rising because of human activities such as the burning of coal, oil, and natural gas. Resulting pollution is visible above Shanghai, China.

Consider This What is the difference between the green- house effect and the enhanced greenhouse effect? Why might one be considered “good” while the other is viewed more as a problem?

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for about 80 percent of human-caused Co2 emissions. Most of the remaining 20 percent comes from changes in the land surface, primarily deforestation. trees, like all living organ- isms, are made mostly of carbon; when forests are burned to clear land, the carbon in the trees is released as Co2.

the uSGCRP report says that the current trajectory of rising GHG concentrations is push- ing the climate into uncharted territory. Co2 levels are much higher today than at any other time in at least 800,000 years. through all those millennia, there has been a clear correla- tion between Co2 concentrations and global temperatures, adding geological support for the strong connection between changes in the strength of the greenhouse effect and the earth’s surface temperature.

Scientists are certain that the burning of fossil fuels is the main source of the recent spike in C in the atmosphere. Multiple, independent lines of evidence clearly link human actions to increased GHG concentrations. Moreover, there is strong evidence that this human-induced rise in atmospheric GHGs is the main reason that the Earth has been warming in recent decades. the uSGCRP report says, “the global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Human fingerprints also have been iden- tified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture, and Arctic sea ice.” the u.S. national Academy of Sci- ences draws the same conclusion: “Many lines of evidence support the conclusion that most of the observed warming since the start of the 20th century, and especially the last several decades, can be attributed to human activities.”

Looking Ahead the more GHGs humans release into the atmosphere, the stronger the enhanced greenhouse effect will become. Scenarios in which GHGs continue to be added to the atmosphere by human activities could cause additional warming of 2 to 11.5 °F over the next century, depending on how much more GHGs are emitted and how strongly the climate system responds to them. Although the range of uncertainty for future temperatures is large, even the lower end of the range is likely to have many undesirable effects on natural and human systems.

Land areas warm more rapidly than oceans, and higher latitudes warm more quickly than lower latitudes. therefore, regional temperature increases may be greater or less than global averages, depending on location. For example, the united States is projected to experience more warming than average, and the Arctic is expected to experience the most warming.

the future climate depends largely on the actions taken in the next few decades to reduce and eventually eliminate human-induced Co2 emissions. In 2005, the u.S. national Academy of Sciences joined with 10 other science academies from around the world in a statement calling on world leaders to take “prompt action” on climate change. the statement was explicit about our ability to limit climate change: “Action taken now to reduce significantly the build-up of greenhouse gases in the atmosphere will lessen the magnitude and rate of climate change.”

Changing Climate: Theory to Reality Although “climate change” and “global warming” are often used interchangeably, rising temperatures are just one aspect of climate change. to understand why, it is important to

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distinguish between “weather” and “climate.” the climate is the average weather over a long period of time. A simple way to think of this is: weather is what determines if you will use an umbrella today; climate determines whether you own an umbrella. thus, when looking at climate change and its impacts, it is important to consider more than just global temperature trends. Changes in the climate other than average temperatures have more direct impacts on nature and society.

the uSGCRP report says, “Climate changes are underway in the united States and are pro- jected to grow,” and “Widespread climate-related impacts are occurring now and are expected to increase.” Sea level rise, the loss of sea ice, changes in weather patterns, more drought and heavy rainfall, and changes in river flows are among the documented changes in the united States. Climate change also threatens ecosystems and public health.

Dr. Jane Lubchencko, the Administrator of the national Atmospheric and oceanographic Administration, has said, “Climate change is happening now and it’s happening in our own backyards and it affects the kinds of things people care about.”

More Extreme Weather Extreme weather events have become more common in recent years, and this trend will con- tinue in the future. Climate change has a significant effect on local weather patterns and, in turn, these changes can have serious impacts on human societies and the natural world.

Stronger Hurricanes Scientists have confirmed that hurricanes are becoming more intense. Since hurricanes draw their strength from the heat in ocean surface waters, hurricanes have the potential to become more powerful as the water warms. A recent peer-reviewed assessment of the link between hurricanes and climate change concluded that “higher resolution modeling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre.”

this trend toward stronger hurricanes is noteworthy because of the vulnerability of coastal communities to these extreme events. the uSGCRP report says, “Sea-level rise and storm surge place many u.S. coastal areas at increasing risk of erosion and flooding [. . .] Energy and transportation infrastructure and other property in coastal areas are very likely to be adversely affected.” In recent years the massive destruction caused by Hurricane Katrina in the united States and by Cyclone nargis, which devastated Burma in 2008, provide painful reminders of this vulnerability.

Hotter, Wetter Extremes Average temperatures are rising, but extreme temperatures are rising even more: in recent decades, hot days and nights have grown more frequent and cold days and nights less fre- quent. there have been more frequent heat waves and hotter high temperature extremes.

In the united States, the uSGCRP report says, “Many types of extreme weather events, such as heat waves and regional droughts, have become more frequent and intense during the past 40 to 50 years.” More rain is falling in extreme events now compared to 50 years ago, resulting in more frequent flash flooding. In 1994 and 2008, the u.S. Midwest experienced

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flooding so severe that each event was considered a 500-year flood—a level of flooding so rare that it would not be expected to occur more than once in five centuries! In May 2010, the city of nashville, tennessee, experienced the worst flooding in its history, enduring what the u.S. Army Corps of Engineers declared a 1,000-year flood. nearly the entire central city was underwater for the first time. The Tennessean—nashville’s principal daily newspaper— reported that the flood cost the city a year’s worth of economic productivity. Individually, these events might be random occurrences, but they are part of a clear, long-term trend of increasing very heavy rainfall in the united States over the past 50 years.

In 2003, Europe experienced a heatwave so hot and so long that scientists estimated that such an extreme event had not occurred there in at least 500 years. that heat wave caused more than 30,000 excess deaths throughout southern and central Europe. A similarly historic heat wave struck Russia and other parts of Eastern Europe in the summer of 2010, killing thou- sands of people and destroying a large fraction of Russia’s wheat crop. Since Russia is a large grain exporter, its crop losses drove up food prices globally.

Although there is no way to determine whether an individual weather event was caused by human-induced climate change, the types of events discussed here are the types of events that scientists have predicted will become more common in a warmer climate. therefore, the events that actually occur are useful indicators of our vulnerabilities to project impacts and can teach us about the likely effects of climate change on our lives.

Too Much or Too Little: Effects on Water Climate change will alter the quantity and quality of available fresh water and increase the frequency and duration of floods, droughts, and heavy precipitation events. Although climate change will affect different regions in different ways, it is generally expected that dry regions of the world will get drier and wet regions will get wetter.

More Floods and Droughts A number of factors are expected to contribute to more frequent floods. More frequent heavy rain events will result in more flooding. Coastal regions will also be at risk from sea level rise and increased storm intensity. While some regions will suffer from having too much water, others will suffer from having too little. Diminished water resources are expected in semi- arid regions, like the western united States, where water shortages often already pose chal- lenges. Areas affected by drought are also expected to increase. As the atmosphere becomes warmer, it can hold more water, increasing the length of time between rain events and the amount of rainfall in an individual event. As a result, areas where the average annual rainfall increases may also experience more frequent and longer droughts.

Altered Availability and Quality Warmer temperatures threaten the water supplies of hundreds of millions of people who depend on water from the seasonal melting of mountain ice and snow in several ways: by increasing the amount of seasonal melt from glaciers and snowpack, by increasing the amount of precipitation that falls as rain instead of snow, and by altering the timing of snowmelt. In the near term, the melting of mountain ice and snow may cause flooding; in the long term, the loss of these frozen water reserves will significantly reduce the water available for humans, agriculture, and energy production. Earlier snowmelt brings other impacts. Western states

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have experienced a six-fold increase in the amount of land burned by wildfires over the past three decades because snowmelt has occurred earlier and summers are longer and drier.

Climate change will affect the quality of drinking water and impact public health. As sea level rises, saltwater will infiltrate coastal freshwater resources. Flooding and heavy rainfall may overwhelm local water infrastructure and increase the level of sediment and contaminants in the water supply. Increased rainfall could also wash more agricultural fertilizer and municipal sewage into coastal waters, creating more low-oxygen “dead zones” in the Chesapeake Bay and the Gulf of Mexico.

Effects on Human Health Climate change is expected to affect human health directly—from heat waves, floods, and storms—and indirectly—by increasing smog and ozone in cities, contributing to the spread of infectious diseases, and reducing the availability and quality of food and water. the uSGCRP report says that children, the elderly, and the poor are at the greatest risk of negative health impacts in the united States.

the u.S. Centers for Disease Control and Prevention have identified a number of health effects associated with climate change, including an increase in heat-related illnesses and deaths from more frequent heat waves, a rise in asthma and other respiratory illnesses due to increased air pollution, higher rates of food- and water-related diseases, and an increase in the direct and indirect impacts of extreme weather events, like hurricanes.

Threats to Ecosystems Climate change is threatening ecosystems around the world, affecting plants and animals on land, in oceans, and in freshwater lakes and rivers. Some ecosystems are especially at risk, including the Arctic and sub-Arctic because they are sensitive to temperature and likely to experience the greatest amount of warming; coral reefs because they are sensitive to high water temperatures and ocean acidity, both of which are rising with atmospheric Co2 lev- els; and tropical rainforests because they are sensitive to small changes in temperature and precipitation.

Clear evidence exists that the recent warming trend is already affecting ecosystems. Entire ecosystems are shifting toward the poles and to higher altitudes. this poses unique chal- lenges to species that already live at the poles, like polar bears, as well as mountain-dwelling species already living at high altitudes. Spring events, like the budding of leaves and migra- tion of birds, are occurring earlier in the year. Different species are responding at different rates and in different ways, which has caused some species to get out of sync with their food sources. the risks to species increase with increasing temperatures; scientists say that an additional 2 °F of warming will increase the risk of extinction for up to 30 percent of species.

Shrinking Arctic Sea Ice Arctic sea ice has seen dramatic declines in recent years. In 2007, Arctic sea ice shrank to its smallest summertime extent ever observed, opening the northwest Passage for the first time in human memory. this new sea ice minimum came only a few months after a study reported that since the 1950s, summer sea ice extents have declined three times faster than projected

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by climate models. In the summer of 2010, Arctic sea ice set a new kind of record: It decreased to the lowest volume ever observed. While the extent (the area of the Arctic ocean covered by ice) in 2010 was slightly higher than in 2007, the ice was considerably thinner in 2010, mak- ing the volume lower than in 2007. Scientists are concerned that this historically low volume of ice could be more susceptible to melting in the future, causing sea ice loss to accelerate.

the importance of sea ice decline comes from the role it plays in both the climate system and large Arctic ecosystems. Snow and ice reflect sunlight very effectively, while open water tends to absorb it. As sea ice melts, the earth’s surface will reflect less light and absorb more. Conse- quently, the disappearance of Arctic ice will actually intensify climate change.

Moreover, as the edge of the sea ice retreats farther from land during the summer, many marine animals that depend on the sea ice, including seals, polar bears, and fish, will lose access to their feeding grounds for longer periods. Eventually, this shift will deprive these organisms of their food sources and their populations will not be sustained.

If warming continues, scientists are sure that the Arctic ocean will become largely free of ice during the summer. Depending in part on the rate of future greenhouse gas emissions, the latest model projec- tions indicate that the opening of the Arc- tic is likely to occur sometime between the 2030s and 2080s. the opening of the Arctic has enormous implications, ranging from global climate disruption to national security issues to dramatic ecological shifts. the Arctic may seem far removed from our daily lives, but changes there are likely to have serious global implications.

Apply Your Knowledge the consequences of abrupt climate change have become so worrisome that some scientists, politicians, and even environmentalists have begun to call for more research into a technique known as geoengineering to help address the problem. Geoengineering is the deliberate intervention and modification of Earth systems to prevent or reduce climate change. For example, some clouds can reflect incoming sunlight, and so one geoengineering scheme is designed to increase the number of clouds in the sky to help cool the planet. the debate over geoengineering is focused on a number of questions:

• Is this a practical and realistic way to address climate change? • Could geoengineering schemes solve one issue (climate change) while triggering other,

potentially more serious problems? • Wouldn’t it be better and more direct to address the root causes of climate change—

greenhouse gas emissions—than to pursue geoengineering?

Consider This Based on what you know about how the greenhouse effect works, why does con- verting a surface of ice and snow to open water lead to a further intensification of climate change? Scientists call this a feed- back effect; why do you think they chose this term?

(continued)

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Rising Sea Level Among the most serious and potentially catastrophic effects of climate change is sea level rise, which is caused by a combination of the “thermal expansion” of ocean water as it warms and the melting of land-based ice. to date, most climate-related sea level rise can be attributed to thermal expansion. Going forward, however, the largest potential source of sea level rise comes from melting land-based ice, which adds water to the oceans. By the end of the century, if nothing is done to rein in GHG emissions, global sea level could be three to six feet higher than it is today, depending on how much land-based ice melts. Moreover, if one of the polar ice sheets on Greenland or West Antarctica becomes unstable because of too much warming, sea level is likely to continue to rise for more than a thousand years and could rise by 20 feet or more, which would permanently flood virtually all of America’s major coastal cities.

Even small amounts of sea level rise will have severe impacts in many low-lying coastal com- munities throughout the world, especially when storm surges are added on top of sea level rise. High population densities and low elevations make some regions especially vulnerable, including Bangladesh and the nile River Delta in Egypt. In the united States, about half of the population lives near the coast. the most vulnerable areas are the Mid-Atlantic and Gulf Coasts, especially the Mississippi Delta. Also at risk are low-lying areas and bays, such as north Carolina’s outer Banks, much of the Florida Coast, and California’s San Francisco Bay and Sacramento/San Joaquin Delta.

Loss of Glaciers, Ice Sheets, and Snow Pack Land-based snow and ice cover are declining because of climate change and contributing to sea level rise. Mountain glaciers at all latitudes are in retreat, from the Himalayas in Central

Apply Your Knowledge (continued) First, review the following sources of information on geoengineering:

• A Discovery news article on how the debate over geoengineering is splitting the scien- tific community: http://news.discovery.com/earth/global-warming/geoengineering -climate-change-121021.htm

• Web pages for Geoengineering Watch and the oxford Geoengineering Programme that provide detailed information on this concept: http://www.geoengineeringwatch.org/ and http://www.geoengineering.ox.ac.uk/

• An article from Nature magazine on geoengineering and environmental ethics: http://www.nature.com/scitable/knowledge/library/geoengineering-and -environmental-ethics-80061230

After reviewing this material, what is your assessment of geoengineering as a potential solu- tion to the challenge of climate change? If you were a scientist interested in the possible costs and benefits of geoengineering, what kind of research would you want to conduct to help bet- ter inform decisions about this approach? Pick one specific example of a geoengineering tech- nique and design a scientific experiment to assess both its possible effectiveness and potential problems.

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Asia to the Andes in tropical South America to the Rockies and Sierras in the western united States. As a conse- quence of warming, many mountain glaciers will be gone by mid-century; Glacier national Park, for example, will likely lose its glaciers by 2030.

the polar ice sheets on Greenland and Antarctica have both experienced net losses of ice in recent years. Melting polar ice sheets add billions of tons of water to the oceans each year. Recent peer-reviewed research found that the Greenland Ice Sheet is losing ice twice as fast as scientists had previously estimated and ice loss has accelerated on both Greenland and Antarctica over the past decades.

Antarctica is losing ice to the melt- ing and slipping of glacier ice into the ocean at a rate enhanced by climate change. Scientists who study the ice sheet fear that the loss of ice could be accelerated by rising sea levels and the warming of ocean water around the fringe of the ice sheet, which rests on the seabed around the coast of West Antarctica. Beyond some threshold amount of warming, the ice sheet could become unstable and ongoing rapid sea level rise could then be unstop- pable. not knowing exactly what level of warming would destabilize this ice sheet calls for caution in how much more warming we allow.

What Can Be Done the GHGs that are already in the atmosphere because of human activity will continue to warm the planet for decades to come. In other words, some level of continued climate change is inevitable, which means humanity is going to have to take action to adapt to a warming world. However, it is still possible—and necessary—to reduce the magnitude of climate change. A growing body of scientific research has clarified that climate change is already underway and some dangerous impacts have occurred. Avoiding much more severe impacts in the future requires large reductions in human-induced Co2 emissions in the coming decades. Conse- quently, many governments have committed to reduce their countries’ emissions by between 50 and 85 percent below 2000 levels by 2050. Global emissions reductions on this scale will

Lisi Niesner/Reuters/Corbis

© Ashley Cooper/Corbis

Evidence of global warming is clearly visible in the rapid disappearance of mountain glaciers over just a few decades, such as the Pasterze Glacier in Austria (top) or the Athabasca glacier in Canada (bottom). The signs in the photos mark the position of the glaciers in 1980 and 1942, respectively.

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reduce the costs of damages and of adaptation, and will dramatically reduce the probability of catastrophic outcomes.

Adapted from Global Warming and Global Climate Change, Center for Climate and Energy Solutions. 2011. Climate Change 101: Science and Impacts. Available online at: http://www.c2es.org/science-impacts/climate-change-101. Used by permission of the Center for Climate and Energy Solutions, www.c2es.org.

Apply Your Knowledge the u.S. Environmental Protection Agency (EPA) has begun to track industrial and energy facilities that emit large quantities of greenhouse gases (GHGs) into the atmosphere. the EPA Greenhouse Gas Reporting Program web page provides detailed information on GHG emis- sions from nine types of industries. For this assignment, follow these steps:

1. Visit the program web page here: http://www.epa.gov/ghgreporting/ 2. Click on the GHG Data Publication tool (click the map). 3. Choose your state from the “view facilities in your state” drop-down list. 4. Zoom into an area near where you live to see if there are any major emitting facilities in

that region. 5. Change the “data view” selection in the upper right corner to view your state data as a

list, as a bar chart, or as a pie chart. 6. Lastly, choose your county or other counties from the “Browse to a County” drop-down

list and see how emissions vary by industry type at the local level.

once you’ve spent some time exploring this site and examining the available data, consider these questions:

• How many large emitting facilities are located in your area? Did you know of their pres- ence before this?

• Which industry type was most responsible for greenhouse gas emissions in your area? Is that what you would expect, or were you surprised by these results?

• How might the data available on this site be useful to scientists and others working to understand greenhouse gas emissions and their connection to climate change?

7.3 Climate Change and World Food Supplies Chapters 2, 3, 4, and 5 helped lay the foundation for a better understanding of how population growth, agricultural practices, land use, and water management all contribute to environmen- tal and social change. In a world where population could reach 9, 10, or 11 billion later this century, it will already be a challenge to meet global food demand. Add to that the fact that current approaches to agriculture, land use, and water management are actually undermining the productivity of our food system, and we have an enormous challenge on our hands. To make matters even worse, climate change is already altering precipitation patterns and changing conditions for farming in many regions of the world. We could think of this as a “perfect storm” of population growth, environmental degradation, and climate change all coming together to threaten our ability to feed the world in the decades ahead.

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This article by John Vidal of the British media outlet the observer reviews some of the current and projected impacts of climate change on food supplies on a region-by-region basis. It demon- strates that while not all of the changes will be negative, the overall impact on agriculture and food supplies of a changing climate will be for the worse. This is especially true of the impacts of climate change on food production systems in some of the poorest regions of the world. While humans have been able to adapt to climate changes in the past, the rate of current change that we are already seeing combined with a much larger population suggests that adaptation has its limits. What is needed is a more aggressive global effort to address the major causes of climate change (see Chapter 8) and simultaneous investment in improving the productivity and resil- iency of food production systems in poorer regions of the world.

By John Vidal When the tunisian street vendor, Mohamed Bouazizi, set himself on fire on 17 December 2010, it was in protest at heavy-handed treatment and harassment in the province where he lived. But a host of new studies suggest that a major factor in the subsequent uprisings, which became known as the Arab spring, was food insecurity.

Drought, rocketing bread prices, food and water shortages have all blighted parts of the Mid- dle East. Analysts at the Centre for American Progress in Washington say a combination of food shortages and other environmental factors exacerbated the already tense politics of the region. As the Observer reports today, an as-yet unpublished uS government study indicates that the world needs to prepare for much more of the same, as food prices spiral and long- standing agricultural practices are disrupted by climate change.

“We should expect much more political destabilisation of countries as it bites,” says Richard Choularton, a policy officer in the un’s World Food Programme climate change office. “What is different now from 20 years ago is that far more people are living in places with a higher cli- matic risk; 650 million people now live in arid or semi-arid areas where floods and droughts and price shocks are expected to have the most impact.

“the recent crises in the Horn of Africa and Sahel may be becoming the new normal. Droughts are expected to become more frequent. Studies suggest anything up to 200 million more food- insecure people by 2050 or an additional 24 million malnourished children. In parts of Africa we already have a protracted and growing humanitarian disaster. Climate change is a creep- ing disaster,” he said.

the Mary Robinson climate justice foundation is hosting a major conference in Dublin this week. Research to be presented there will say that rising incomes and growth in the global population, expected to create 2 billion more mouths to feed by 2050, will drive food prices higher by 40–50%. Climate change may add a further 50% to maize prices and slightly less to wheat, rice and oil seeds.

“We know population will grow and incomes increase, but also that temperatures will rise and rainfall patterns will change. We must prepare today for higher temperatures in all sec- tors,” said Gerald nelson, a senior economist with the International Food Policy Research Institute in Washington.

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All of the studies suggest the worst impacts will be felt by the poorest people. Robinson, the former Irish president, said: “Climate change is already having a domino effect on food and nutritional security for the world’s poorest and most vulnerable people. Child malnutrition is predicted to increase by 20% by 2050. Climate change impacts will disproportionately fall on people living in tropical regions, and particularly on the most vulnerable and marginalised population groups. this is the injustice of climate change—the worst of the impacts are felt by those who contributed least to causing the problem.”

Apply Your Knowledge the issue of global climate change raises a number of ethical issues. For example, greenhouse gas emissions by individuals in the present are causing climate change impacts that affect peo- ple in the future, people who have no say or input into the decisions we make and the actions we take today. Review this reading on Ethics and Global Climate Change (http://www.nature .com/scitable/knowledge/library/ethics-and-global-climate-change-84226631). What are the main points being made by the authors? Should ethical considerations play a role in deciding what, if anything, we should do to address climate change?

But from Europe to the uS to Asia, no population will remain insulated from the huge changes in food production that the rest of the century will bring.

Frank Rijsberman, head of the world’s leading Cgiar crop research stations, said: “there’s a lot of complacency in rich countries about climate change. We must understand that instabil- ity is inevitable. We already see a lot of refugees. Perhaps if a lot of people come over on boats to Europe or the uS that would wake them up.”

Impacts on Asia and Oceania China is relatively resilient to climate change. Its population is expected to decline by up [to] 400 million people this century, easing demand on resources, and it has the capacity to buy in vast quantities of food.

But because more and more Chinese are changing to a more meat-based diet, its challenges will be land and cattle feed. Climate change will affect regions in different ways, but many crops are expected to migrate northwards.

Crop losses are increasingly being caused by extreme weather events, insect attacks and dis- eases. the 2011 drought lifted food prices worldwide. Wheat is becoming harder to grow in some northern areas of China as the land gets drier and warmer.

In southern China, droughts in recent years have replaced rainy seasons. the national acad- emy of agricultural sciences expects basic food supplies to become insufficient around the year 2030.

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A new study for uS Aid expects most of Vietnam, Cambodia, Laos and thailand to see 4–6C temperature rises by 2050. the Lower Mekong region of 100 mil- lion people, which is prone to weather extremes, could also see rainfall increase 20% or more in some areas, reducing the growth of rice and other staple crops. Many provinces will see food production decline significantly. the number of malnourished chil- dren in the region may increase by 9 to 11 million by 2050.

Extreme events will increasingly affect agriculture in Australia. Key food-growing regions in the south are likely to experience more droughts in the future, with part of western Austra- lia having already experienced a 15% drop in rainfall since the mid-1970s.

the number of record-breaking hot days in Australia has doubled since the 1960s, also affect- ing food output.

Impacts on Europe Climate change affects agricultural production through its effects on the timing, intensity and variability of rainfall and shifts in temperatures and carbon dioxide concentrations.

Crops normally seen growing in the south of Europe will be able to be grown further north. this would allow more sweetcorn, grapes, sunflowers, soya and maize to be grown in Britain. In Scotland, livestock farming could become more suitable. At the higher latitudes warmer temperatures are predicted to lengthen and increase the intensity of the growing season. But more Co2 and a major temperature rise could cut yields by around 10% later in the century.

Latest Eu projections suggest the most severe consequences of climate change will not be felt until 2050. But significant adverse impacts are expected earlier from more frequent and prolonged heatwaves, droughts and floods. Many crops now grown in southern Europe, such as olives, may not survive high temperature increases. Southern Europe will have to change the way it irrigates crops.

In Europe’s high and middle latitudes, global warming is expected to greatly expand the grow- ing season. Crops in Russia may be able to expand northwards but yields will be much lower because the soils are less fertile. In the south, the climate is likely to become much drier which will reduce yields. In addition, climate change is expected to make water resources scarcer and encourage weeds and pests.

In 2011, Russia banned wheat and grain exports after a heatwave. Warming will increase for- est fires by 30-40%. this will affect soil erosion and increase the probability of floods.

© Bryan Denton/Corbis

Climate change is expected to increase extreme weather events in the Pacific islands. Here, aftermath of Super Typhoon Haiyan’s devastation in the Philippines. It was one of the most powerful typhoons ever recorded, with sustained winds of nearly 200 mph.

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In the Middle East and north Africa, declining yields of up to 30% are expected for rice, about 47% for maize and 20% for wheat.

Impacts on the Americas the uS is expected to grow by 120 million people by 2050. Government scientists expect more incidents of extreme heat, severe drought, and heavy rains to affect food production. the warming is expected to continue without undue problems for 30 years but beyond 2050 the effects could be dramatic with staple crops hit.

According to the latest government report: “the rising incidence of weather extremes will have increasingly negative impacts on crop and livestock productivity, because critical thresh- olds are already being exceeded.” Many agricultural regions of the uS will experience declines.

California’s central valley will be hard hit with sunflowers, wheat, tomato, rice, cotton and maize expected to lose 10–30% of their yields, especially beyond 2050. Fruit and nut crops which depend on “winter chilling” days may have to relocate. Animals exposed to many hot nights are increasingly stressed. Many vegetable crops will be hit when temperatures rise only a few degrees above normal.

nearly 20% of all uS food is imported, so climate extremes elsewhere will also have an effect. In 2011, 14.9% of uS households did not have secure food supplies and 5.7% had very low food security.

Because few crops can withstand average temperature rises of more than 2C, Latin America expects to be seriously affected by a warming climate and more extreme weather. Even mod- erate 1–2C rises would cause significant damage to Brazil, one of the world’s biggest suppli- ers of food crops. Brazilian production of rice, beans, manioc, maize and soya are all expected to decline, with coffee especially vulnerable.

other studies suggest Brazil’s massive soya crop, which provides animal feed for much of the world, could slump by more than 25% over the next 20 years.

two major crops should do well: quinoa and potatoes.

Impacts on Africa Many African countries are already experiencing longer and deeper droughts, floods and cyclones. the continent is expected to suffer disproportionately from food insecurity, due to fast-growing vulnerable populations.

Egypt expects to lose 15% of its wheat crops if temperatures rise 2C, and 36% if the increase is 4C. Morocco expects crops to remain stable up to about 2030, but then to drop quickly later. Most north African countries traditionally import wheat and are therefore highly vulnerable to price shocks and droughts elsewhere.

A new study of 11 west African countries expects most to be able to grow more food as tem- peratures rise and rainfall increases. But demand from growing populations may double food

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prices. Climate change may mean nigeria, Ghana and togo can grow and export more sor- ghum, raised for grain.

temperatures are expected to rise several degrees in regions close to the Sahel. In Burkina Faso, the sorghum crop is expected to decline by 25% or more, but maize yields may improve.

other studies by IFPRI suggest crop yields across sub-Saharan Africa may decline 5–22% by 2050, pushing large numbers of people deeper into destitution.

A new un study suggests climatic conditions in southern Africa will worsen. Climate models mostly predict an increase in annual maximum temperatures in the region of 1 to 2C by 2050. this will favour some crops but shift others to higher ground or further north.

Both of Africa’s staple crops, maize and sorghum, are expected to be badly hit by increasing severity of weather.

oxfam warns that small-scale farmers in the Horn of Africa will bear the brunt of the nega- tive impacts of climate change. unpredictable weather here has already left millions semi- destitute and dependent on food aid.

From Vidal, J. (2013, April 13). Climate change: How a warming world is a threat to our food supplies. the observer. Retrieved from http://www.theguardian.com/environment/2013/apr/13/climate-change-threat-food-supplies Copyright Guardian News & Media Ltd 2007. Used by permission.

7.4 Stratospheric Ozone Depletion The issues of global climate change and stratospheric ozone depletion are often confused and assumed to be the same problem. In fact, stratospheric ozone depletion is fundamentally a separate issue from climate change even though there are some areas of overlap. In this read- ing, staff writers with the U.S. Environmental Protection Agency (EPA) explain the importance of the Earth’s stratospheric ozone layer and review the major causes of ozone depletion in recent decades.

Ozone is a molecule made up of three oxygen atoms. In the troposphere, where we live and breathe, ozone is considered a dangerous pollutant (see section 9.1) that can aggravate respira- tory conditions and damage lung tissue. However, in the stratosphere, 15–30 kilometers above the Earth’s surface, an abundance of ozone known as the ozone layer serves a very useful pur- pose. The stratospheric ozone layer absorbs a significant percentage of UVB radiation coming from the sun. UVB radiation is known to cause skin cancer and cataracts and to harm plant and marine life. For this reason, it’s been said that ozone is “good up high, but bad nearby.”

Ozone in the stratosphere naturally undergoes a process of destruction and re-creation as it is bombarded by solar UVB radiation and is also broken down by naturally occurring chlorine that can occasionally reach the stratosphere. This process of creation and destruction can be likened to a bathtub half filled with water, with the faucet on but the drain also open. As long as water

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is flowing into the bathtub (ozone creation) at the same rate it is being drained out (ozone destruction), the level of water (ozone) in the bathtub will stay the same.

In the 1970s scientists began to speculate that a class of chemical compounds known as chloro- fluorocarbons (CFCs) could be affecting the ozone layer. They hypothesized that because CFCs (which contain chlorine) were so stable, they could be carried by winds and air updrafts to the stratosphere where powerful UVB radiation could break them apart, releasing chlorine. This extra chlorine could speed up ozone depletion and reduce the process of ozone creation— essentially opening the bathtub drain a little more and slowing the rate of water coming out of the faucet.

By the 1980s, scientists working in Antarctica measured large seasonal declines in stratospheric ozone over that continent, giving rise to the phrase “ozone hole.” Satellite-based instruments measuring ozone concentrations in terms of Dobson Units—a unit of measure developed spe- cifically to determine ozone density—confirmed this trend, and further sampling of chlorine in the stratosphere determined that CFC-based chlorine was responsible for most of the decline in ozone concentrations. In response to this scientific evidence, the nations of the world agreed to the Montreal Protocol in 1987, which eventually led to the phase out of most ozone-depleting substances (ODSs) worldwide. The case of ozone depletion is one of the rare instances where nations around the world responded cooperatively to a truly global environmental challenge. As a result, there is some indication that the ozone layer is recovering from recent low levels and that a major global environmental catastrophe may have been averted. The question that many environmental scientists and others ask themselves is why we were able to gain consensus and take action to address ozone depletion so quickly compared to our lack of action on climate change. You’ll have a chance to ask yourself this very question in the Critical thinking and Dis- cussion Questions section at the end of this chapter.

By Staff for the Environmental Protection Agency (EPA) the Earth’s ozone layer protects all life from the sun’s harmful radiation, but human activities have damaged this shield. Less protection from ultraviolet light will, over time, lead to higher skin cancer and cataract rates and crop damage. the u.S., in cooperation with 190 other coun- tries, is phasing out the production of ozone-depleting substances in an effort to safeguard the ozone layer.

The Ozone Layer the Earth’s atmosphere is divided into several layers. the lowest region, the troposphere, extends from the Earth’s surface up to about 10 kilometers (km) in altitude. Virtually all human activities occur in the troposphere. Mt. Everest, the tallest mountain on the planet, is only about 9 km high. the next layer, the stratosphere, continues from 10 km to about 50 km. Most commercial airline traffic occurs in the lower part of the stratosphere.

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[M]ost atmospheric ozone is concentrated in a layer in the stratosphere, about 15–30 kilo- meters above the Earth’s surface. ozone is a molecule containing three oxygen atoms. It is blue in color and has a strong odor. normal oxygen, which we breathe, has two oxygen atoms and is colorless and odorless. ozone is much less common than normal oxygen. out of each 10 million air molecules, about 2 million are normal oxygen, but only 3 are ozone.

Figure 7.4: The ozone layer

the ozone layer is found in the lower stratosphere about 15–30 km above the Earth’s surface. Its importance to humanity stems from stratospheric ozone’s ability to absorb a portion of the sun’s uVB radiation, which has been linked to various types of skin cancer and cataracts and can harm crops and some marine life.

However, even the small amount of ozone plays a key role in the atmosphere. the ozone layer absorbs a portion of the radiation from the sun, preventing it from reaching the planet’s surface. Most importantly, it absorbs the portion of ultraviolet light called uVB. uVB has been linked to many harmful effects, including various types of skin cancer, cataracts, and harm to some crops, certain materi- als, and some forms of marine life.

Consider This How do small numbers of ozone molecules in the stratosphere, more than 10 kilome- ters above the Earth’s surface, help protect life on Earth?

Troposphere

Stratosphere

Ozone layer

Earth

Mt. Everest

9 km

10 km

50 km Ozone layer

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At any given time, ozone molecules are constantly formed and destroyed in the stratosphere. the total amount, however, remains relatively stable. the concentration of the ozone layer can be thought of as a stream’s depth at a particular location. Although water is constantly flowing in and out, the depth remains constant.

While ozone concentrations vary naturally with sunspots, the seasons, and latitude, these processes are well understood and predictable. Scientists have established records span- ning several decades that detail normal ozone levels during these natural cycles. Each natural reduction in ozone levels has been followed by a recovery. Recently, however, convincing sci- entific evidence has shown that the ozone shield is being depleted well beyond changes due to natural processes.

Ozone Depletion For over 50 years, chlorofluorocarbons (CFCs) were thought of as miracle substances. they are stable, nonflammable, low in toxicity, and inexpensive to produce. over time, CFCs found uses as refrigerants, solvents, foam blowing agents, and in other smaller applications. other chlorine-containing compounds include methyl chloroform, a solvent, and carbon tetrachlo- ride, an industrial chemical. Halons, extremely effective fire extinguishing agents, and methyl bromide, an effective produce and soil fumigant, contain bromine. All of these compounds have atmospheric lifetimes long enough to allow them to be transported by winds into the stratosphere. Because they release chlorine or bromine when they break down, they damage the protective ozone layer. the discussion of the ozone depletion process below focuses on CFCs, but the basic concepts apply to all of the ozone-depleting substances (oDS).

In the early 1970s, researchers began to investigate the effects of various chemicals on the ozone layer, particularly CFCs, which contain chlorine. they also examined the potential impacts of other chlorine sources. Chlorine from swimming pools, industrial plants, sea salt, and volcanoes does not reach the stratosphere. Chlorine compounds from these sources readily combine with water and repeated measurements show that they rain out of the tropo- sphere very quickly. In contrast, CFCs are very stable and do not dissolve in rain. thus, there are no natural processes that remove the CFCs from the lower atmosphere. over time, winds drive the CFCs into the stratosphere.

the CFCs are so stable that only exposure to strong uV radiation breaks them down. When that happens, the CFC molecule releases atomic chlorine. one chlorine atom can destroy over 100,000 ozone molecules. the net effect is to destroy ozone faster than it is naturally created. to return to the analogy comparing ozone levels to a stream’s depth, CFCs act as a siphon, removing water faster than normal and reducing the depth of the stream.

Large fires and certain types of marine life produce one stable form of chlorine that does reach the stratosphere. However, numerous experiments have shown that CFCs and other widely-used chemicals produce roughly 84% of the chlorine in the stratosphere, while natu- ral sources contribute only 16%.

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Consider This What is the relative importance of natu- ral causes and human releases of CFCs in contributing to stratospheric ozone deple- tion? What is it about CFCs that help make them so effective at destroying ozone in the stratosphere?

Large volcanic eruptions can have an indirect effect on ozone levels. Although Mt. Pinatubo’s [in the Philippines] 1991 eruption did not increase stratospheric chlorine concentrations, it did produce large amounts of tiny particles called aerosols (different from consumer prod- ucts also known as aerosols). these aero- sols increase chlorine’s effectiveness at destroying ozone. the aerosols only increased depletion because of the pres- ence of CFC-based chlorine. In effect, the aerosols increased the efficiency of the CFC siphon, lowering ozone levels even more than would have otherwise occurred. unlike long-term ozone depletion, however, this effect is short-lived. the aerosols from Mt. Pinatubo have disappeared, but satellite, ground-based, and balloon data still show ozone depletion occurring closer to the historic trend.

The Ozone Hole one example of ozone depletion is the annual ozone “hole” over Antarctica that has occurred during the Antarctic Spring since the early 1980s. Rather than being a literal hole through the layer, the ozone hole is a large area of the stratosphere with extremely low amounts of ozone. ozone levels fall by over 60% during the worst years.

Apply Your Knowledge Given that the ozone layer is 15–30 kilometers (9–18 miles) above the Earth’s surface, how is it possible for scientists to know just how CFCs are impacting ozone concentrations? using your understanding of the scientific method, write out some possible approaches that sci- entists may have used to study this issue. It often takes a significant amount of time from when scientists first hypothesize a problem—such as the connection between CFCs and ozone depletion—and when they can actually collect enough evidence to support that hypothesis. Given that, should politicians always wait until a significant amount of research is completed or should they act in advance? What are the dangers of waiting until the science is close to completely settled? What are the dangers of acting too far in advance?

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In addition, research has shown that ozone depletion occurs over the latitudes that include north America, Europe, Asia, and much of Africa, Australia, and South America. over the u.S., ozone levels have fallen 5–10%, depending on the season. thus, ozone depletion is a global issue and not just a problem at the South Pole.

Reductions in ozone levels will lead to higher levels of uVB reaching the Earth’s surface. the sun’s output of uVB does not change; rather, less ozone means less protection, and hence more uVB reaches the Earth. Studies have shown that in the Antarctic, the amount of uVB measured at the surface can double during the annual ozone hole. Another study confirmed the relationship between reduced ozone and increased uVB levels in Canada during the past several years.

Laboratory and epidemiological studies demonstrate that uVB causes nonmelanoma skin cancer and plays a major role in malignant melanoma development. In addition, uVB has been linked to cataracts. All sunlight contains some uVB, even with normal ozone levels. It is always important to limit exposure to the sun. However, ozone depletion will increase the amount of uVB, which will then increase the risk of health effects. Furthermore, uVB harms some crops, plastics and other materials, and certain types of marine life.

September 17, 1979 October 7, 1989

October 9, 2006 October 1, 2010

NASA

The ozone layer protects Earth from the sun’s deadly radiation. Here, changes in the hole above Antarctica since 1979 are shown. The dark blue and purple colors are indicative of high levels of ozone loss. The use of chlorofluorocarbons was a key driver in creating the hole in the ozone layer.

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SECtIon 7.5Case history—Carbon dioxide and oCean aCidifiCation

The World’s Reaction the initial concern about the ozone layer in the 1970s led to a ban on the use of CFCs as aero- sol propellants in several countries, including the u.S. However, production of CFCs and other ozone-depleting substances grew rapidly afterward as new uses were discovered.

through the 1980s, other uses expanded and the world’s nations became increasingly con- cerned that these chemicals would further harm the ozone layer. In 1985, the Vienna Con- vention was adopted to formalize international cooperation on this issue. Additional efforts resulted in the signing of the Montreal Protocol in 1987. the original protocol would have reduced the production of CFCs by half by 1998.

After the original Protocol was signed, new measurements showed worse damage to the ozone layer than was originally expected. In 1992, reacting to the latest scientific assessment of the ozone layer, the Parties to the Protocol decided to completely end production of halons by the beginning of 1994 and of CFCs by the beginning of 1996 in developed countries.

Because of measures taken under the Montreal Protocol, emissions of ozone-depleting sub- stances are already falling. Levels of total inorganic chlorine in the stratosphere peaked in 1997 and 1998. the good news is that the natural ozone production process will heal the ozone layer in about 50 years.

Adapted from ozone Science: the Facts Behind the Phaseout. United States Environmental Protection Agency. Retrieved from http://www.epa.gov/ozone/science/sc_fact.html

7.5 Case History—Carbon Dioxide and Ocean Acidification For the past few decades climate scientists have been puzzled by an inconsistency between the rate of human emissions of carbon dioxide (CO2) to the atmosphere and the rate of increase in atmospheric concentrations of this gas. Based on the amount of fossil fuel we knew we were burning, scientists expected atmospheric CO2 levels to be increasing faster than they actually were. Some scientists dubbed this the “missing carbon” problem. It turns out that a significant portion of the excess CO2 that we were emitting into the air was being absorbed by the world’s oceans, an apparently fortunate fact that has helped to moderate increases in global tempera- ture. However, it also turns out that the uptake of CO2 by the seas is changing the very chemistry of the oceans, perhaps in highly destructive ways.

In this article, science reporter Carl Zimmer summarizes the results of recent research on how changes in acidity can play a huge role in the health and productivity of the seas. This research relied heavily on the analysis of ancient sediment taken from the sea floor. This sediment pro- vides a snapshot of what the oceans were like over millions of years. What scientists have found is that when the oceans are relatively non-acidic, there is an abundance of marine life supported by single-celled organisms with shells of calcium carbonate (what chalk is made from). Over millions of years these organisms lived, died, and sank to the bottom of the ocean leaving lay- ers of white sediment that today can be seen as white cliffs in some locations. However, this same research shows that when oceans turn even moderately more acidic, the white sediment

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is replaced with red clay, suggesting a massive change in the chemistry, productivity, and biodi- versity of the world’s oceans.

Much of the excess CO2 that we are currently emitting to the atmosphere is being absorbed by the oceans where it is changing ocean chemistry and making these bodies of water more acidic. In this way CO2 is not only changing the climate but also changing the oceans. The consequences of such a change could be dramatic and devastating, adding even more urgency to the need to address greenhouse gas emissions. The next chapter will review a variety of approaches to using energy more efficiently and meeting our energy needs in new ways that offers some hope for reducing CO2 emissions.

By Carl Zimmer the JOIDES Resolution looks like a bizarre hybrid of an oil rig and a cargo ship. It is, in fact, a research vessel that ocean scientists use to dig up sediment from the sea floor. In 2003, on a voyage to the southeastern Atlantic, scientists aboard the JOIDES Resolution brought up a particularly striking haul.

they had drilled down into sediment that had formed on the sea floor over the course of mil- lions of years. the oldest sediment in the drill was white. It had been formed by the calcium carbonate shells of single-celled organisms—the same kind of material that makes up the White Cliffs of Dover. But when the scientists examined the sediment that had formed 55 mil- lion years ago, the color changed in a geological blink of an eye.

“In the middle of this white sediment, there’s this big plug of red clay,” says Andy Ridgwell, an earth scientist at the university of Bristol.

In other words, the vast clouds of shelled creatures in the deep oceans had virtually disappeared. Many sci- entists now agree that this change was caused by a drastic drop of the ocean’s pH level. the seawater became so cor- rosive that it ate away at the shells, along with other species with calcium carbonate in their bodies. It took hun- dreds of thousands of years for the oceans to recover from this crisis, and for the sea floor to turn from red back to white.

A Warning for the Future the clay that the crew of the JOIDES Resolution dredged up may be an omi- nous warning of what the future has in store. By spewing carbon dioxide into the air, we are now once again making the oceans more acidic.

Ira Block/National Geographic Creative

A researcher holds a replica of the core sample showing an abrupt change in sea floor sediment approximately 55 million years ago. Scientists believe a catastrophic drop in oceanic pH levels, known as the Paleocene-Eocene thermal maximum, was responsible for the widespread death of calcium carbonate bodied sea creatures.

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today, Ridgwell and Daniela Schmidt, also of the university of Bristol, are publishing a study in the journal Natural Geoscience, comparing what happened in the oceans 55 million years ago to what the oceans are experiencing today. their research supports what other researchers have long suspected: the acidification of the ocean today is bigger and faster than anything geologists can find in the fossil record over the past 65 million years. Indeed, its speed and strength—Ridgwell estimate[s] that current ocean acidification is taking place at ten times the rate that preceded the mass extinction 55 million years ago—may spell doom for many marine species, particularly ones that live in the deep ocean.

“this is an almost unprecedented geological event,” says Ridgwell.

When we humans burn fossil fuels, we pump carbon dioxide into the atmosphere, where the gas traps heat. But much of that carbon dioxide does not stay in the air. Instead, it gets sucked into the oceans. If not for the oceans, climate scientists believe that the planet would be much warmer than it is today. Even with the oceans’ massive uptake of Co2, the past decade was still the warmest since modern record-keeping began. But storing carbon dioxide in the oceans may come at a steep cost: It changes the chemistry of seawater.

At the ocean’s surface, seawater typically has a pH of about 8 to 8.3 pH units. For comparison, the pH of pure water is 7, and stomach acid is around 2. the pH level of a liquid is determined by how many positively charged hydrogen atoms are floating around in it. the more hydrogen ions, the lower the pH. When carbon dioxide enters the ocean, it lowers the pH by reacting with water.

the carbon dioxide we have put into the atmosphere since the Industrial Revolution has low- ered the ocean pH level by .1. that may seem tiny, but it’s not. the pH scale is logarithmic, meaning that there are 10 times more hydrogen ions in a pH 5 liquid than one at pH 6, and 100 times more than pH 7. As a result, a drop of just .1 pH units means that the concentration of hydrogen ions in the ocean has gone up by about 30 percent in the past two centuries.

The Impacts of Ocean Acidification to see how ocean acidification is going to affect life in the ocean, scientists have run labora- tory experiments in which they rear organisms at different pH levels. the results have been worrying—particularly for species that build skeletons out of calcium carbonate, such as cor- als and amoeba-like organisms called foraminifera. the extra hydrogen in low-pH seawater reacts with calcium carbonate, turning it into other compounds that animals can’t use to build their shells.

these results are worrisome, not just for the particular species the scientists study, but for the ecosystems in which they live. Some of these vulnerable species are crucial for entire ecosys- tems in the ocean. Small shell-building organisms are food for invertebrates, such as mollusks and small fish, which in turn are food for larger predators. Coral reefs create an underwater rain forest, cradling a quarter of the ocean’s biodiversity.

But on their own, lab experiments lasting for a few days or weeks may not tell scientists how ocean acidification will affect the entire planet. “It’s not obvious what these mean in the real world,” says Ridgwell.

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one way to get more information is to look at the history of the oceans themselves, which is what Ridgwell and Schmidt have done in their new study. At first glance, that history might suggest we have nothing to worry about. A hundred million years ago, there was over five times more carbon dioxide in the atmosphere and the ocean was .8 pH units lower. Yet there was plenty of calcium carbonate for foraminifera and other species. It was during this period, in fact, that shell-building marine organisms produced the limestone formations that would eventually become the White Cliffs of Dover.

But there’s a crucial difference between the Earth 100 million years ago and today. Back then, carbon dioxide concentrations changed very slowly over millions of years. those slow changes triggered other slow changes in the Earth’s chemistry. For example, as the planet warmed from more carbon dioxide, the increased rainfall carried more minerals from the mountains into the ocean, where they could alter the chemistry of the sea water. Even at low pH, the ocean contains enough dissolved calcium carbonate for corals and other species to survive.

today, however, we are flooding the atmosphere with carbon dioxide at a rate rarely seen in the history of our planet. the planet’s weathering feedbacks won’t be able to compensate for the sudden drop in pH for hundreds of thousands of years.

Scientists have been scouring the fossil record for periods of history that might offer clues to how the planet will respond to the current carbon jolt. they’ve found that 55 million years ago, the Earth went through a similar change. Lee Kump of Penn State and his colleagues have estimated that roughly 6.8 trillion tons of carbon entered the Earth’s atmosphere over about 10,000 years.

nobody can say for sure what unleashed all that carbon, but it appeared to have had a drastic effect on the climate. temperatures rose between 5 and 9 degrees Celsius (9 to 16 Fahren- heit). Many deep-water species became extinct, possibly as the pH of the deep ocean became too low for them to survive.

But this ancient catastrophe (known as the Paleocene-Eocene thermal maximum, or PEtM) was not a perfect prequel to what’s happening on Earth today. the temperature was warmer before the carbon bomb went off, and the pH of the oceans was lower. the arrangement of the continents was also different. the winds blew in different patterns as a result, driving the oceans in different directions. All these factors make a big difference on the effect of ocean acidification. For example, the effect that low pH has on skeleton-building organisms depends on the pressure and temperature of the ocean. Below a certain depth in the ocean, the water becomes so cold and the pressure so high that there’s no calcium carbonate left for shell- building organisms. that threshold is known as the saturation horizon.

to make a meaningful comparison between the PEtM and today, Ridgwell and Schmidt built large-scale simulations of the ocean at both points of time. they created a virtual version of the Earth 55 million years ago and let the simulation run until it reached a stable state. the pH level of their simulated ocean fell within the range of estimates of the pH of the actual ocean 55 millions years ago. they then built a version of the modern Earth, with today’s arrange- ments of continents, average temperature, and other variables. they let the modern world reach a stable state and then checked the pH of the ocean. once again, it matched the real pH found in the oceans today.

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Ridgwell and Schmidt then jolted both of these simulated oceans with massive injections of carbon dioxide. they added 6.8 trillion tons of carbon over 10,000 years to their PEtM world. using conservative projections of future carbon emissions, they added 2.1 trillion tons of car- bon over just a few centuries to their modern world. Ridgwell and Schmidt then used the model to estimate how easily carbonate would dissolve at different depths of the ocean.

the results were strikingly different. Ridgwell and Schmidt found that ocean acidification is happening about ten times faster today than it did 55 million years ago. And while the satura- tion horizon rose to 1,500 meters 55 million years ago, it will lurch up to 550 meters on aver- age by 2150, according to the model.

A New Wave of Extinctions? the PEtM was powerful enough to trigger widespread extinctions in the deep oceans. today’s faster, bigger changes to the ocean may well bring a new wave of extinctions. Paleontologists haven’t found signs of major extinctions of corals or other carbonate-based species in surface waters around PEtM. But since today’s ocean acidification is so much stronger, it may affect life in shallow water as well. “We can’t say things for sure about impacts on ecosystems, but there is a lot of cause for concern,” says Ridgwell.

Ellen thomas, a paleoceanographer at Yale university, says that the new paper “is highly sig- nificant to our ideas on ocean acidification.” But she points out that life in the ocean was buf- feted by more than just a falling pH. “I’m not convinced it’s the whole answer,” she says. the ocean’s temperature rose and oxygen levels dropped. together, all these changes had complex effects on the ocean’s biology 55 million years ago. Scientists now have to determine what sort of combined effect they will have on the ocean in the future.

our carbon-fueled civilization is affecting life everywhere on Earth, according to the work of scientists like Ridgwell—even life that dwells thousands of feet underwater. “the reach of our actions can really be quite global,” says Ridgwell. It’s entirely possible that the ocean sedi- ments that form in the next few centuries will change from the white of calcium carbonate back to red clay, as ocean acidification wipes out deep-sea ecosystems.

“It will give people hundreds of millions of years from now something to identify our civiliza- tion by,” says Ridgwell.

Adapted from Zimmer, C. (2010). An Ominous Warning on the Effects of Ocean Acidification. Yale Environment 360. Retrieved from http://e360.yale.edu/feature/an_ominous_warning_on_the__effects_of_ocean_acidification /2241/ Copyright Carl Zimmer. Reprinted by permission of the author.

Summary & Resources

Chapter Summary It’s been said that Earth has a “Goldilocks” or “just right” atmosphere, due to mild and habit- able temperatures. nearby planets of Venus and Mars are incredibly hotter or colder than our planet. this difference cannot be explained by distance from the sun, but instead it is due mostly to the atmospheric composition of each planet. For example, greenhouse gases in a planet’s atmosphere, such as carbon dioxide, act as an insulating blanket and help trap

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infrared or heat energy as it leaves a planet’s surface. the atmosphere of Venus is made up mainly of carbon dioxide, so its surface temperature is nearly 1,000 °F. Mars has almost no greenhouse gases, so its surface temperature is a frigid –120 °F. In contrast, water vapor and small quantities of carbon dioxide and other greenhouse gases help keep the Earth’s average surface temperature at a comfortable 59 °F.

What concerns scientists is the degree to which human activities, such as the burning of fossil fuels, enhance this natural greenhouse effect and causes global warming and global climate change. Because the global climate system is so vast and complex, there are areas of uncer- tainty over the causes and consequences of climate change. Scientists have had to grapple with whether the observed warming of Earth’s atmosphere in recent decades is a result of human factors or due to natural causes. Additionally, researchers are investigating whether recent changes in weather patterns in different parts of the world can be linked to climate change.

Given that the possible consequences of climate change have the potential to impact so many people, the politics of the issue are complicated. Because climate change is a global envi- ronmental problem, it will require global cooperation to address it. However, nations of the world have (to date) made very limited progress as they try to agree on how to tackle climate change. this is due to sharp differences in beliefs over what should be done and who should pay for it.

In contrast, the global community was able to agree on how to address a different global envi- ronmental challenge, that of stratospheric ozone depletion. While the ozone depletion issue was also complex in its own way, the causes were more easily understood, the consequences more imminent, and the solutions more straightforward than those for climate change. As a result, action was swifter and more effective on this issue than it has been for climate change.

there are a number of key lessons that we can take away from the study of climate change and stratospheric ozone depletion. Global environmental challenges are highly complex, and scientific understanding of causes and effects often takes years to research. In the meantime, while waiting for more definitive scientific proof, the problem can worsen and perhaps even become irreversible. Policymakers must therefore decide whether to take action in the face of such uncertainty. Efforts to address ozone depletion through the Montreal Protocol highlight such action, as they began long before there was solid evidence linking the problem to CFCs. Action on climate change has been slower, in part, because the science is even more compli- cated and the political and economic stakes are much higher than for ozone depletion. Since one of the major contributors to climate change is the combustion of fossil fuels, proposals to deal with this problem have focused largely on the development of energy sources that do not emit greenhouse gases. the next chapter will review these energy sources, the challenges facing them, and their potential to help address the climate change issue.

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Working Toward Solutions At an international level the Kyoto Protocol (http://unfccc.int/kyoto_protocol/items/2830 .php) is the primary governmental effort to address the issue of climate change. First adopted in 1997, the Kyoto Protocol entered into force as a global treaty in 2005 and, as of Decem- ber 2012, 190 countries had ratified the treaty. the united States is the only country to sign the protocol but not ratify it, whereas Canada ratified the treaty but then withdrew from it. the Kyoto Protocol sets internationally binding greenhouse gas emission reduction targets on signatory countries, with more ambitious reduction targets for developed nations. Although India and China have both ratified the Kyoto Protocol, they are currently not obligated to reduce their greenhouse gas emissions. this is because they are both considered developing countries and their historical contributions to increased greenhouse gas concentrations have been minimal. overall, the Kyoto Protocol appears to have had very little impact on reducing greenhouse gas emissions. International climate change negotiations continue to be charac- terized by disputes over financial responsibility, the scale and timing of meeting reduction targets, and other procedural issues regarding the future of negotiations.

Political efforts to address and respond to climate change at the national level in the united States have arguably gone even worse than at the international level. Even though the united States was a signatory to the Kyoto Protocol in 1997, neither President Clinton, President Bush, nor President obama have made an effort to have it ratified by the u.S. Senate. other legislative efforts to address greenhouse gas emissions and climate change at the federal level have also gone nowhere. nevertheless, the u.S. Environmental Protection Agency and other federal agencies such as the Department of Defense are taking what they call “com- mon-sense steps” to reduce greenhouse gas emissions (http://www.epa .gov/climatechange /EPAactivities.html). these include efforts to improve energy efficiency, expand the use of renewable energy, and advance climate change science.

While the u.S. federal government has been slow to act on the issue of climate change, the same cannot be said for many state and local governments. For example, nine states in the northeast have formed a Regional Greenhouse Gas Initiative (http://www.rggi.org/), the first “market-based regulatory program in the united States to reduce greenhouse gas emissions.” California adopted a cap-and-trade program in 2013 (http://www.arb.ca.gov/cc/capandtrade /capandtrade.htm) that allows polluting industries to buy and sell greenhouse gas emission permits from each other, while gradually reducing overall emission levels over time. other states are developing climate action plans, setting renewable energy targets, and promoting energy efficiency in homes and businesses to help reduce greenhouse gas emissions.

Private companies and institutions such as colleges and universities are also increasingly taking steps to lower their greenhouse gas emissions. these companies and institutions are motivated both by a desire to do what they can to avoid climate change as well as by the financial savings that usually come from reducing energy use. For example, in 2009 the Busi- ness Roundtable released a report (http://businessroundtable.org/studies-and-reports/the -balancing-act-climate-change-energy-security-and -the-u.s.-economy/) outlining how mem- ber companies could both reduce greenhouse gas emissions and increase profitability. Like- wise, the American College and university Presidents’ Climate Commitment (http://www .presidentsclimatecommitment.org/) now has over 600 schools that have signed on to inventory their greenhouse gas emissions and develop climate action plans to significantly reduce their

(continued)

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Post-test

1. the greenhouse effect is a natural phenomenon. a. true b. False

2. Major scientific assessments have determined that natural causes could be respon- sible for much of the observed changes to climate in recent decades.

a. true b. False

3. Food insecurity and rising food prices were a major factor in the unrest and upris- ings known as the Arab Spring

a. true b. False

4. the ozone layer that protects life on Earth is located primarily in what region of the atmosphere?

a. troposphere b. Mesosphere c. Stratosphere d. Ionosphere

5. Scientific research has revealed that excess carbon dioxide emissions are making the oceans less acidic.

a. true b. False

6. the most common greenhouse gas after water vapor is a. methane. b. nitrogen. c. carbon dioxide. d. chlorofluorocarbons.

7. Climate change can be expected to result in stronger hurricanes and more extreme weather events.

a. true b. False

Working Toward Solutions (continued) emissions. Lastly, individuals can take many small, but potentially cumulative, actions to reduce their own greenhouse gas emissions. the u.S. EPA provides a comprehensive guide (http://www.epa .gov/climatechange/wycd/) for what individuals can do at home, at work, at school, and on the road.

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8. Climate change will allow farmers in southern Europe to grow many crops now only grown in northern Europe.

a. true b. False

9. Which of the following is the best explanation of how the ozone layer protects life on Earth?

a. the ozone layer blocks incoming sunlight and prevents global warming. b. the ozone layer absorbs outgoing infrared energy and increases surface temperatures. c. the ozone layer absorbs uVB radiation from the sun that can cause skin cancer. d. the ozone layer shields sea ice from the sun and protects it from melting.

10. the primary concern among scientists over ocean acidification is that a. acidic sea water will cause sea level rise. b. acidic sea water will corrode the hulls of ships. c. acidic sea water prevents aquatic organisms from building calcium carbonate shells. d. acidic sea water changes the texture and flavor of ocean caught fish.

Answers 1. a. true. the answer can be found in section 7.1. 2. b. False. the answer can be found in section 7.2. 3. a. true. the answer can be found in section 7.3. 4. c. Stratosphere. the answer can be found in section 7.4. 5. b. False. the answer can be found in section 7.5. 6. c. carbon dioxide. the answer can be found in section 7.1. 7. a. true. the answer can be found in section 7.2. 8. b. False. the answer can be found in section 7.3. 9. c. the ozone layer absorbs uVB radiation from the sun that can cause skin cancer. the answer can be found in section 7.4. 10. c. acidic sea water prevents aquatic organisms from building calcium carbonate shells. the answer can be found in section 7.5.

Key Ideas • Scientific understanding of the connection between greenhouse gases and the

Earth’s climate dates back to the 19th century. However, it’s only been in the past few decades that concern has grown over the possibility that higher atmospheric concentrations of carbon dioxide and other greenhouse gases could lead to abrupt and catastrophic climate change.

• there is consistent and accumulating scientific evidence that global average tem- peratures are increasing and that this increase is due in large part to higher concen- trations of greenhouse gases—carbon dioxide (Co2), methane (CH4), and nitrous oxide (n2o)—from human activities. Continued emissions of these gases into the atmosphere could result in additional increases in global average temperatures of between 2 and 11.5 degrees Fahrenheit over the next century.

• Scientists refer to the addition of greenhouse gases to the atmosphere as the “enhanced greenhouse effect,” since it adds to the planet’s natural greenhouse effect. While this enhanced greenhouse effect does raise global average temperatures, sci- entists prefer the term “global climate change” over “global warming” because it also contributes to changes in wind patterns, precipitation, and other climate factors.

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• Some of the major impacts of global climate change that are projected occur—or that are already being observed—include more extreme weather, disruptions to water supply and water quality, negative impacts to human health, increased rates of extinction and biodiversity loss, and sea level rise.

• Climate change is already impacting precipitation, water supply, and food produc- tion in many regions of the world. Some of the regions where climate change will have the biggest negative impacts on food production are already among the poorest in the world.

• Climate change mitigation involves taking steps to reduce and eventually halt emis- sions of heat-trapping greenhouse gases into the atmosphere. In contrast, climate change adaptation accepts that some climate change has already occurred and that more is almost certain to occur in the decades ahead. therefore, adaptation involves making changes to how and where we live, where we grow food and secure our water, and other aspects of life in response to a changing climate.

• the ozone layer is located in the lower stratosphere roughly 15–30 kilometers above the Earth’s surface. the ozone layer helps to absorb a significant amount of the sun’s uVB radiation, protecting life on Earth from the harm that this radiation can cause.

• Chlorine from a class of chemicals known as chlorofluorocarbons (CFCs) has been found to deplete concentrations of ozone in the stratosphere, resulting in increased levels of uVB radiation reaching the Earth’s surface. Faced with strong scientific evidence for ozone depletion caused by CFCs, nations of the world took action to eliminate CFC use.

• Increased levels of carbon dioxide emissions from fossil fuel burning and other human activities is leading to changes in ocean acidity, making our seas more acidic. these changes could be catastrophic and lead to sharp declines in the productivity and biodiversity of the world’s oceans.

Critical thinking and Discussion Questions

1. think back to the discussion in the Introduction to this book of how the scientific method might be used to answer questions about the connection between road salt application and the death of trees. Scientists studying an issue like that face a fair amount of complexity in understanding the connections between salt application and tree mortality. Consider how much more complex the study of global climate must be. Scientists have observed that global average temperatures have increased at the same time that atmospheric levels of carbon dioxide have increased. What must these scientists do to try to discern whether one is caused by the other? What other factors might complicate their research?

2. the “debate” over global climate change is really based on a series of debates or questions about what is happening, what’s causing it, and what we should do about it. Specifically, there are three separate questions that scientists, politicians, and oth- ers find themselves grappling with: • Is the Earth getting warmer? Is the climate changing? • If the climate is changing, are human actions the primary cause of that change,

or can this be explained by natural causes? • If the climate is changing and human actions are the primary cause of that

change, what can or should be done about it?

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As suggested in the Introduction to this chapter, the first two questions are largely positive in nature; that is, they are questions about the way the world is. When scien- tists state that global average temperatures have increased by 1.5 degrees in the last century, and that this increase “is due primarily to human-induced increases in heat- trapping gases,” they are simply stating the results of their scientific research. When politicians use that information to argue for a change in policy to reduce greenhouse gas emissions, they move from the positive to the normative, making statements about the way the world should be. unfortunately, many climate change scientists have found themselves attacked personally and professionally for their research, and some major politicians in the united States have gone so far as to accuse the scien- tific community of engaging in a vast conspiracy to fool the American public about climate change. Given what you know about the scientific method and how it gov- erns the work of scientists, how do you feel about these political attacks on scien- tists? Should the checks and balances of the scientific method—hypothesis testing, peer review of research results—shield scientists from these sorts of accusations? Would an acceptance of a “yes” answer to the first two questions above—the world is warming and it’s due primarily to human activities—still leave room for a wide range of opinion and debate over question 3—what to do about it?

3. Given the changes that have already occurred to climate and the likelihood that no matter what we do additional climate change will occur in the decades ahead, the idea of adaptation to climate change takes on a new significance. What are some major ways that human society might have to adapt to a world with more extreme weather, sea level rise, water shortages, and changing disease patterns? Many experts point to the recent example of Hurricane Sandy as an indicator of what we could expect more of in the future. How could coastal areas like new York and new Jersey better prepare and adapt to increased frequency of storms like Sandy? Do wealthier countries—who are most responsible for increased greenhouse gas concentrations—have a moral obligation to help poorer countries adapt to climate change impacts?

4. Faced with growing scientific evidence of the link between CFC use and stratospheric ozone depletion, governments of the world took swift and dramatic action to begin the phaseout of CFCs and other ozone-depleting substances. As a result of this action there is some evidence that the ozone layer is beginning to recover. In contrast, and despite growing scientific evidence, nations of the world have made very little prog- ress in addressing or resolving the issue of global climate change. What might be some of the explanations for this difference in response? What is it about the causes, consequences, and solutions to each of these problems that could explain such dra- matically different responses?

5. the reading on ocean acidification raised the possibility that much of the marine life we know could be wiped out in a few centuries if current trends continue. What would be some of the most significant impacts of such a change? What groups might be most affected if this were to occur? Does the danger of ocean acidification add even more urgency to the need to move away from fossil fuels?

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Key terms

adaptation Making changes so as to become suitable to a new or special applica- tion or situation.

attribution Assigning some quality or char- acter to a person or thing.

Dobson Units A unit of measure developed specifically to determine ozone density.

geoengineering the deliberate interven- tion and modification of earth systems to prevent or reduce climate change.

greenhouse effect the global warming of our atmosphere caused by the presence of carbon dioxide and other greenhouse gases, which trap the sun’s radiation.

Kyoto Protocol An international treaty that stipulates highly developed countries must cut their emissions of carbon dioxide and other gases that cause climate warming by an average of 5.2 percent by 2012.

Montreal Protocol An international treaty designed to protect the ozone layer by phas- ing out the production of numerous sub- stances believed to be responsible for ozone depletion.

normative claim A claim about what some- one values; a statement of the way things should be.

ozone layer A layer in the Earth’s strato- sphere containing a high concentration of ozone, which absorbs most of the ultraviolet radiation from the sun.

positive claim A claim based on actual evi- dence; a statement of what we know.

stratosphere the layer of the atmosphere between the troposphere and the meso- sphere that contains a layer of ozone that protects life on earth by filtering out much of the sun’s ultraviolet radiation.

stratospheric ozone depletion the reduc- tion of the protective layer of ozone in the upper atmosphere by chemical pollution.

troposphere the lowest region of the atmosphere, extending from the Earth’s sur- face to a height of about 33,000 ft (10 km).

UVB radiation the part of the electro- magnetic spectrum with wavelengths just shorter than visible light; a high-energy form of radiation that can have damaging or lethal effects on organisms with higher levels of exposure.

Additional Resources there are a number of good resources available on the basic science behind the greenhouse effect and global climate change. Perhaps the most authoritative voice on this subject is the Intergovernmental Panel on Climate Change (IPCC). the IPCC (http://www.ipcc.ch/) is the leading international body for the assessment of climate change issues. note that the IPCC is charged with assessment of climate change science; they do not conduct their own research. Rather, they compile and attempt to make sense of the thousands of individual stud- ies conducted by scientists globally on this subject. the IPCC publishes highly detailed and comprehensive assessment reports on the science behind climate change, its impacts, and possible solutions (http://www.ipcc.ch/publications_and_data/publications_and_data_reports .shtml#.us9Y5fRDsy4). Particularly useful is a list of Frequently Asked Questions to which the IPCC provides answers (http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faqs .html). At the national level, the united States Global Change Research Program (uSGCRP)

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coordinates federal research into climate change issues (http://www.globalchange.gov/). Like the IPCC, the uSGCRP has a number of publications available that provide detailed infor- mation on climate change issues as they relate specifically to the united States (http://www .globalchange.gov/resources/reports). the Center for Climate and Energy Solutions (C2ES) is an excellent source of information on basic climate change science and some of the pos- sible solutions to this challenge (http://www.c2es.org/). In particular, their Climate Change 101 Series does a great job of distilling the complex science behind climate change down to a level that’s accessible and understandable for most readers (http://www.c2es.org/science -impacts/climate-change-101). the national Aeronautics and Space Administration (nASA) has a site that shows recent and archived images of the ozone hole (http://ozonewatch.gsfc .nasa.gov/). national Geographic maintains a Global Warming page with a lot of good informa- tion (http://environment.nationalgeographic.com/environment/global-warming/), and the Annenberg Learner Project’s Habitable Planet series has a whole unit on this subject (http:// www.learner.org/courses/envsci/unit/text.php?unit=12&secnum=0). the journal Nature provides a fairly scientific and technical piece on the global climate system for readers who want more detail (http://www.nature.com/scitable/knowledge/library/the-global-climate -system-74649049). Lastly, Colorado State university sponsors a site called “100 Views of Cli- mate Change” that includes a wealth of resources on basic climate science, impacts of climate change, and ways to take action (http://changingclimates.colostate.edu/index.html).

In terms of climate change impacts, the online reporting of Yale Environment 360 (http:// e360.yale.edu/topic/climate/005/) presents easily accessible summaries of some of the ways in which climate change is expected to impact, or is already impacting, ecosystems and people. Particularly interesting are reports on a north Pole without ice (http://e360.yale .edu/feature/tipping_point_arctic_heads_to_ice_free_summers/2567/ and http://e360.yale .edu/slideshow/arctic_tipping_point_heading_to_an_ice-free_north_pole/120/1/), the link between climate change and extreme weather (http://e360.yale.edu/feature/whats_with _the_weather_is_climate_change_to_blame/2388/), how climate change is affecting animal behavior (http://e360.yale.edu/feature/with_temperatures_rising_here_comes_global _weirding/2132/), and the impact of climate change on sea level rise (http://e360.yale.edu /feature/battered_new_york_city_looks_for_ways_to_hold_back_the_sea/2589/). nASA pro- vides some very interesting animations and other information on climate change and strato- spheric ozone depletion (http://www.nasa.gov/topics/earth/index.html). one particularly interesting animation shows how much the northern hemisphere has warmed in the past 50 years (http://www.nasa.gov/topics/earth/features/warming-links.html). the New York Times had a series of articles in early 2013 that reported on how 2012 was officially the hottest year on record in the united States, and how climate change was being linked to extreme weather worldwide (http://www.nytimes.com/2013/01/09/science/earth/2012 -was-hottest-year-ever-in-us.html, http://www.nytimes.com/interactive/2013/01/08/science /earth/record-setting-heat-across-the-us-in-2012.html, http://www.nytimes.com/2013/01 /11/science/earth/extreme-weather-grows-in-frequency-and-intensity-around-world .html, and http://www.nytimes.com/slideshow/2013/01/11/science/earth/11extreme -slideshow.html). Lastly, the work of filmmaker Jason Balog illustrates just how rapidly climate change is occurring by documenting the loss of ice from glaciers and the polar regions in his film Chasing Ice (http://vimeo.com/48966552). this short clip shows what is con- sidered the largest glacier break up ever filmed (http://www.guardian.co.uk/environment /video/2012/dec/12/chasing-ice-iceberg-greenland-video).

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there are also many good resources on the politics and economics of climate change, including this report on how many businesses are doing their part to address the climate change issue while increasing profitability at the same time (http://www.c2es.org/publications/business -case-for-climate-legislation). this Yale Environment 360 report also argues that a strong eco- nomic case can be made for reducing carbon emissions (http://e360.yale.edu/feature/the _economic_case_for_slashing_carbon_emissions/2200/). this New York Times op-ed piece by university of California physicist Richard A. Muller describes how he gradually overcame his skepticism about climate change science and came to accept the growing scientific consen- sus around this issue (http://www.nytimes.com/2012/07/30/opinion/the-conversion-of-a -climate-change-skeptic.html). the piece by Muller is especially powerful because it describes how he approached the issue of climate change through the lens of the scientific method and how that helped him accept the importance of this issue. He rightly concludes the article by reminding us that even if we accept the science behind climate change, the real challenge will lie in deciding what we will do about the problem. this interview with South Carolina Repub- lican Bob Inglis reveals just how difficult the politics of this issue can be (http://e360.yale.edu /feature/interview_bob_inglis_conservative_who_believes_climate_change_is_real/2615/). Inglis lost his seat in Congress because of his willingness to state that he believed in human- caused climate change. the World Resources Institute (WRI) provides highly detailed and up- to-date information on the regulatory and political developments related to climate change (http://www.wri.org/our-work/project/us-climate-action). Finally, here are a few other resources that are very useful to the student wishing to learn more about global climate change. this national Science Foundation site has video interviews with over 50 leading cli- mate scientists on a variety of issues (http://www.nsf.gov/news/special_reports/degree/). Climate Central is an independent organization of leading climate scientists whose web page contains a range of resources on this subject (http://www.climatecentral.org). the Climate Literacy and Energy Awareness network (CLEAn) provides a wealth of resources to teachers and other educators on climate change issues (http://cleanet.org/index.html). Climate Con- nections archives stories heard on national Public Radio (nPR) on this subject (http://www .npr.org/series/9657621/climate-connections). this article analyzes the consensus that’s formed around climate change in the scientific literature, demonstrating that over 97 percent of scientific papers published on the subject endorse the consensus view (http://iopscience .iop.org/1748-9326/8/2/024024/article). this article reviews how climate change is causing entire ecosystems to have to shift or experience biodiversity loss and decline (http://www .sciencemag.org/content/341/6145/486.full). Lastly, these three articles cover the basics of “carbon budgeting” and illustrate just how little room is left for a continued reliance on fossil fuels if we are to avoid catastrophic climate change (http://www.bloomberg.com/news/2013 -02-14/the-most-influential-climate-study-few-people-know-about.html, http://www.rolling stone.com/politics/news/global-warmings-terrifying-new-math-20120719, and https:// www1.ethz.ch/iac/people/knuttir/papers/meinshausen09nat.pdf).

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