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Chapter 18

Global Climate Change

Dr. Joao Santos

Chapter 18

Global Climate Change

Dr. Joao Santos

Case History: Potential Consequences of Global Warming

• Approximate 300 year period (1000 to 1300), Earth

was considerably warmer than normal, known as

the Medieval Warming Period (MWP)

• Followed by the Little Ice Age (LIA): Mid 1400 to

1700, difficult for people in Southeast Asia and

Western Europe

• The collapse of the Ankorian civilization part due to

the onset of the LIA

• Crop failures in Western Europe during the LIA, the

population devastated by the Black Plague about

1400

Case History: Potential Consequences of Global Warming

• Famous Viking explorer Eric the Red’s voyage near the end of tenth century, a period of warm climate (Medieval Warming period)

• The Vikings colonized Iceland, Greenland, and northern North America

• Sea temperature probably 4°C (7°F) warmer than now

• Little Ice Age started early fourteenth century, creating treacherous sea conditions, famine, spread of the Black Plague

• Climate changes believed to cause the abandonment of Viking settlements in North America and Greenland

Global Change: An Overview

• Climate changes: Contributing to the complex evolutionary history of the Earth system

• Earth system: Interactions between the atmosphere, the oceans, solid Earth, and the biosphere

• The effects of human activities: Extensive on a global scale

• Apply the better understanding to better manage the environment

Tools for Studying Global Change

• Geologic Records:

• Sediments deposited on floodplains or in lakes, bogs, glaciers, or the ocean

• Carbon dioxide concentration in glacial ice, as old as 800,000 years

• Real-time monitoring: Good for testing models and predictions from prehistoric record

• Mathematical models: Global circulation models (GCMs)

Geologic Record (Marine/Ocean Cores)

Geologic Record (Ice Cores)

Atmosphere and Climate Change

• Atmosphere as a complex chemical factory: with many little-understood chemical reactions

• Many of the reactions strongly influenced by both sunlight and the compounds produced by life

• Climate change: Change of atmosphere conditions and its relationships with lithosphere, hydrosphere, and biosphere

• Changes in greenhouse gases, variable temperature, and water vapor

The Greenhouse Effect (1)

• Temperature of Earth: Determined by three factors

– The amount of sunlight received

– The amount of solar energy reflected and absorbed

– The amount of heat retention by atmosphere

• Earth: Absorbing the short wavelength solar energy, then radiating longer wavelength IR radiation

The Greenhouse Effect (2)

• Several atmospheric gases: Water vapor and several other atmospheric gases, including CO2, CH4, NOx, CFCs, trapping more heat and warming up the lower atmosphere, similar to the effect of a greenhouse

• The concentration of greenhouse gases increased recently due to human activities, anthropogenic gases

Study Past Climate Change

• The Instrumental Record: Started in 1860s, today temperature measured at about 7,000 stations around the world

• The Historical Record: Books, newspapers, journal articles, personal journals

• The Paleo-Proxy Record: Proxy data refers to data that is not strictly climatic but that can be correlated with climate, such as temperature of the land or sea: ice core, tree rings, pollen, corals, carbon-14, carbon dioxide, and methane data

Dendrochronology (Tree Rings)

Carbon Dioxide in the Atmosphere

Global Warming

• Global warming: The observed increase in the average temperature of the near-surface land and ocean environments of Earth

• Human processes (in the past 100 years), as well as natural ones (over geologic time) contributed significantly to global warming

• Recent global warming is believed to be due in a large part to human emissions of greenhouse gases

• Based on equivalent amount of the global warming potential (GWP), carbon dioxide accounted for 85.1 percent, methane 8.2 percent, nitrous oxide 4.6 percent, and chlorofluorocarbons 2.2 percent

Increase in Greenhouse Gasses

Global Temperature Change

• The Pleistocene Ice Age: ~ 2 mya, peaked at 18,000 years ago

• Numerous changes in Earth’s mean annual temperature since then

• Warming trend over the last 140 years, first 8 years of the twenty-first century had the warmest temperatures

• Mean temp increased about 0.8°C (1.36°F) in the past 100 years

Global Temperature Data from the U.S. (NOAA) and Europe (WMO)

Why Climate Change?

• Changes in long cycles (100,000 years) separated by short cycles (23,000 to 41,000 years)

• First identified in 1920s, Milankovitch hypothesis

• Long cycle: The variability in Earth’s orbit around the Sun

• Short cycle: The tilt of Earth’s axis

Milankovitch Cycles and Climate Change

Milankovitch hypothesis – Climate variation over 100- 300 Ka predicted by cyclic changes in orbital geometry.

• The shape of Earth’s orbit varies (~ 100,000 year cyclicity)

• Tilt of Earth’s axis varies from 22.5o to 24.5o (~41,000 years)

• Precession – Earth’s axis wobbles like a top (23,000 years)

Why Climate Change?

• Climate system even unstable in shorter cycles, in a few decades

• The ocean conveyor belt, global circulation of ocean water, contribute to the change

• Discernable human influence, mean

temperature likely 1.5° to 4.5°C (2.6° to 7.8°F) warmer in twenty-first century

• Global warming: Need to consider major forcing variables—solar, volcanic, and anthropogenic gases

Solar Forcing

• Historic record of the past 1000 years showing the variability of solar energy

• Medieval Warm Period (A.D. 1000 to 1300) corresponding to a time increased solar radiation

• The Little Ice Age (fourteenth century) corresponding to the minimum solar activity

• The effect relatively small, 0.25 percent

Volcanic Forcing

• Volcanic eruption: Vast amount of aerosol particles into the air

• Aerosols: Reducing solar radiation to Earth surface

• Episodes of volcanic eruptions having a significant contribution to the cooling of the Little Ice Age

Anthropogenic Forcing

• Natural variability failing to explain the warming at end of the twentieth century

• Mathematical modeling on the anthropogenic

forcing: increase of temperature 2°C due to the doubling of CO2

• Significant global warming as a result of human activities, air pollution reduced incoming solar energy by 10 percent which offsetting up to 50 percent of the expected warming

Potential Effects of Global Climate

• Doubling the greenhouse gases, then 1.5° to 4.5°C (2.6° to 7.8°F) increase in average global temperature

• Significant rise of sea level and melting of glacier ice due to the increase in temp

• The number of retreating glaciers accelerating in many areas of the world (ex. Alaska)

• Significant effects on global climate patterns

Glaciers and Global Warming

• Loose snow has about 90 percent air compared to firm,

with about 25 percent air to glacial ice with less than

20 percent air as bubbles

• Transformation from snow to glacial ice: 10s to 1000s of

years

• Global warming: Accelerated melting of glacial ice

• Exposed bare ground after glacial ice melts produces a

positive feedback cycle: The more ice that melts, the

faster the warming and increased melting

• The lowest extent of sea ice in the Atlantic Ocean in 2007

• The Antarctic Peninsula: One of the most rapidly warming

regions on Earth

Extent of Sea Ice

Change in Climate Patterns

• Global warming leads to significant changes of rainfall and soil moisture (draught and flood)

• Agricultural activities (crop growth cycle) and world food supplies affected greatly by climatic factors (desertification)

• Global warming affects the frequency, intensity, and distribution of natural hazards, such as hurricane and other storms

Sea Level Rise and Global Warming

• An estimated 40 to 200 cm (16 to 80 in.), wide range of rise in sea level for the next century

• Increases in coastal erosion: Up to 260 ft on open beaches by stronger wave actions

• Landward shift of existing estuaries

• Disastrous impact on the existing developments along coastal zones

Biosphere and Global Warming

• Causing a number of changes in biosphere, both people and overall ecosystem

• Risk of extinction due to land-use change and habitat shift

• Spread of infectious and other diseases due to migration of organisms

• Both land and oceanic components affected: from plants, to polar bears, to the bleaching of coral reef

Adaptation of Species to Global Warming

• During the past 25 years or so, plants and animals shifted their ranges by about 6 kilometers per decade toward the polar areas

• Spring arriving earlier, migrating birds arriving earlier, about 2.3 days per decade

• In Costa Rica, over 60 species of frogs may have gone extinct

• Assist migration of some species, unable to migrate with climate change, creating an invasive species, problematic

Strategies for Reducing the Impact of Global Warming (1)

• Identify the historic changes that have occurred

• Predict the potential changes in the future: through modeling and simulation

• Reduce greenhouse gases

• Political commitment: Reconciling the conflicts between the environmental need for reduction of greenhouse gases and the economic demands for more fossil fuel

Strategies for Reducing the Impact of Global Warming (2)

• The Kyoto Protocol, international agreement to reduce emissions of greenhouse gases, signed by 166 nations and became a formal international treaty in February 2005

• Scientific evidence suggests that burning fossil fuels is contributing significantly to global warming

• Even if carbon emissions were reduced to zero, warming will continue this century. There is

0.5° to 1.0°C warming in the system

Strategies for Reducing Global Warming (3)

Reducing the Impact of Global Warming (4)

Reduce the emission of CO2 • Improved engineering technologies of the fuel-

burning power plants

• Use fossil fuels releasing less CO2 • Conservation of energy

• Store CO2 in forests, soils and rocks, depleted oil and gas fields, saltwater aquifers (sequestration of CO2)

• Use alternative energy

End of Chapter 18