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Inside Atlantic Current slowdown 2 Kyoto relocated Carbon Production 2 Cosmic rays and Clouds 4 earth’s sensitivity to Carbon Dioxide 4 Climate Change and body size 5 europe’s Windy future 6
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briefiNgs | Climate Change & Environment
briefiNgs
Scientific American Briefings: Climate Change & Environment consists of
summaries of recent peerreviewed articles from the scientific literature. It draws these
summaries from the journals of Nature Publishing Group, including Nature, Nature Climate Change, Nature Geoscience, Nature Physics and the Nature Reviews journals.
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OCEANOGRAPHY
Atlantic current slowdown ReseaRcheRs have long the- orized that the ocean’s thermo- haline or meridional over- turning circulation — an ocean “conveyor belt” driven by tem- perature and salinity gradients, which includes the warm North Atlantic Gulf Stream — might slow down as a result of climate change. But this has proven dif- ficult to measure.
Uwe Send of the Scripps In- stitution of Oceanography in California, and colleagues, looked at readings from three moored buoys that are part of the Meridional Overturning Variability Experiment (MOVE) array, anchored at either end of a single 1,000-km strip running eastwards from Guadalupe, north of Venezuela. Data from January 2000 to June 2009 showed a 20 percent decrease in deep-ocean southward flow across this line. This is the first direct observation of interan- nual and decadal variability in this current, the team reports.
The slowdown is probably a result of natural variability rather than climate change, the team says, and is likely to reverse within a few years. Under- standing such fluctuations is im- portant for climate prediction, and more data will come from the Rapid Climate Change Project’s array of 20 moored instruments, installed in 2004 between the Canary Islands and the Bahamas.
—Nicola Jones, Nature Climate Change
■■ Geophys. Res. Lett. doi: 10.1029/2011GL049801 (in the press)
ECOLOGY
Moving trees climate change is expected to lead to significant shrinkage
and/or shifting of habitat for many species. As a result there is growing interest in proactive ad- aptation strategies, perhaps the most controversial of which is assisted colonization, in which species are moved to new suit- able habitat that they could not have reached on their own.
Conservation biologist Helen Regan, at the University of Cali- fornia, Riverside, USA, and col- leagues focused on Tecate cy- press, a rare fire-dependant tree found in California. They tracked the impacts of climate change on the tree’s habitat to investigate whether assisted col- onization could help offset threats, such as habitat loss and altered fire regimes.
The results suggest that as- sisted colonization could be an effective risk-minimizing strategy, so long as there are suitable sites nearby and trans- located trees are able to estab- lish successfully. However, as- sisted colonization may be inef- fective where other threats are ongoing, such as where humans have increased the rate or se- verity of fire outbreaks.
—Alastair Brown, Nature Climate Change
■■ Glob. Change Biol. doi: 10.1111/j.1365-2486.2011.02586.x (2011)
EMISSIONS TRADE
The effects of Kyoto the Kyoto Protocol, which came into force in 2005, was the first multilateral attempt to cap carbon emissions. Its effects on
national emissions are debat- able, however, because it may encourage so-called carbon leakage, in which carbon-inten- sive production is relocated out- side national borders.
Rahel Aichele and Gabriel Felbermayr of the University of Munich, Germany, compiled a set of annual data on the carbon footprint — the sum of domestic carbon emissions and net emis- sions embodied in trade — of 40 countries from 1995 to 2007. Their model allowed them to isolate the impact of the pro- tocol commitments on domestic emissions from the impact on the overall carbon footprint. The researchers also estimated the impact of the protocol on the carbon-import ratio — the amount of emissions embodied in imports relative to domestic emissions. An increase in the ratio indicates that carbon leakage has occurred.
They found that, on average, the Kyoto commitments have re- duced domestic emissions by 7 percent, but the carbon-import ratio increased on average by about 14 percent. This implies a substantial relocation of carbon- intensive production; carbon leakage cancelled out the do- mestic savings, rendering carbon footprints unchanged.
—Monica Contestabile, Nature Climate Change
■■ J. Environ. Econ. Manage. doi: 10.1016/ j.jeem.2011.10.005 (2011)
Hillside fires in California.
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On the COver
The North Atlantic Gulf stream, part of the ocean’s thermohaline circulation system, exerts a significant influence on the hemisphere’s climate. Studies have begun to measure its natural variability. See page 2.
Credit: RedAndr/Wikimedia Commons
Scientific American Briefings, Climate Change & Environment, Volume 1, Number 2, February 2012, published monthly by Scientific American, a division of Nature America, Inc., 75 Varick Street, 9th Floor, New York, NY 10013-1917. Subscription rates: 1 year (12 issues) $19.95 (USD). Please send subscription correspondence, including change of e-mail and postal addresses to: Scientific American Briefings, Box 3187, Harlan, IA 51537. E-mail address for subscription inquires: [email protected]. E-mail address for general inquires: [email protected]. Subscription inquires: U.S. and Canada: 800-333-1199; other: +1-515-248-7684.
Copyright © 2012 Scientific American, a division of Nature America, Inc. All rights reserved.
FORESTRY
Selective logging tRopical defoRestation
contributed about 16 percent of the total anthropogenic carbon emissions between 2000 and 2006. In addition to releasing carbon into the atmosphere, de- forestation changes land surface reflectivity, which affects regional temperature and precipitation patterns. Reduced-impact log- ging, which selects certain valu- able trees, is intended to mini- mize disruption of the forest canopy, but the effect of this log- ging practice on land–atmosphere carbon exchange has not been well quantified.
Scott Miller of the Atmospheric Sciences Research Center at the State University of New York, US, and co-workers measured carbon dioxide exchange and various eco- logical parameters to investigate the effects of selective logging on carbon exchange in an old-growth Amazonian forest.
Results suggest that the log- ging caused small decreases in primary production, leaf produc- tion and latent heat flux, and in- creases in respiration, tree mor- tality and wood production. The net effect of reduced-impact log- ging was short lived and effects were barely discernible after only one year. The authors suggest that reduced-impact logging provides
a potential strategy for managing tropical forest that minimizes risks to the climate.
—Alastair Brown, Nature Climate Change
■■ Proc. Natl Acad. Sci. USA doi: 10.1073/ pnas.1105068108 (2011)
tECHNOLOGY
Liquid hydrogen fuel-cell caRs — which run on hydrogen and emit only water from their tailpipes — offer a compelling way to reduce trans- port emissions. However, manu- facturers have struggled to find ways of safely storing enough hy- drogen in a car for long journeys.
Researchers have now taken a step towards an alternative: storing the hydrogen as a liquid. University of Oregon chemist Shih-Yuan Liu and colleagues re- port the creation of a new mate- rial: BN-methylcyclopentane, a five-membered cyclic amine bo- rane that is a stable liquid at room temperature and pressure. When a cheap iron chloride cata-
lyst is added, three of these rings chemically join together, re- leasing hydrogen in the process.
Liu’s work was funded by a US Department of Energy project that is aiming to develop a viable liquid or solid storage mechanism for hydrogen fuel by 2017. The team is now working to make recycling of their starting material cheaper and more energy efficient.
—Nicola Jones, Nature Climate Change
■■ J. Am. Chem. Soc. doi: 10.1021/ ja208834v (2011)
clIMATOlOGY
Teak record for Burma theRe aRe few long-term in- strument-based climate records in Asia, so researchers turn to natural records instead. This in- cludes tree rings from species, such as teak, that have identifi- able rings from the wet and dry seasons in the tropics. In 2010, a tree-ring atlas of droughts and monsoons in Asia over the last 1,000 years was published but some countries were not repre- sented in the regional study.
Now, Rosanne D’Arrigo of the Tree-Ring Laboratory at the Lamont-Doherty Earth Observa- tory in New York, and colleagues, have looked at teak samples from Burma’s Maingtha Reserve Forest, revealing a climate record stretching from 1613 to 2009. Their results match well with those from neighboring coun- tries, D’Arrigo’s team reports. They recommend stitching to- gether more such records, al- though intense logging makes it hard to find long-lived trees.
—Nicola Jones, Nature Climate Change
■■ Geophys. Res. Lett. doi: 10.1029/2011GL049927 (in the press) Science doi: 10.1126/ science.1185188 (2010)
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ASTROphYSIcS
Cloud maker
do cosmic rays and solar ac- tivity affect our climate? Re- searchers have proposed that cosmic rays, which hit Earth in greater quantities when sunspot activity lulls, might help to nu- cleate cloud particles and thus cool the Earth. A long-antici- pated particle physics experi- ment designed to test this link — CLOUD (Cosmics Leaving Out- door Droplets) — has now yielded its first results.
The experiment, based at Eu- rope’s particle-physics labora- tory CERN, near Geneva in Swit- zerland, uses a particle beam to mimic cosmic rays in an ultra- clean steel cloud chamber, where temperature, water vapor and other atmospheric constitu- ents can be carefully controlled. The team aims to quantify the roles of various gases in nucle- ating the precursors of cloud particles, so that these numbers can be plugged into climate models.
CERN’s Jasper Kirkby and colleagues report that sulphuric acid and ammonia vapors can enhance nucleation by up to a factor of ten under the condi- tions they studied. However, the nucleation rate within CLOUD was, surprisingly, only one tenth to one thousandth of what hap- pens in the real world, so other vapors — perhaps amines —
must play a big role. CLOUD will tackle that question next.
—Nicola Jones, Nature Climate Change
■■ Nature doi: 10.1038/nature10343 (2011)
MODElING
Slower warming how much will our planet warm if carbon dioxide levels double from pre-industrial levels? In other words, what is the planet’s “sensitivity” to carbon dioxide?
This has proven a hard ques- tion to answer, mainly because of uncertainty about how aero- sols and the ocean alter heating effects. The 2007 Intergovern- mental Panel on Climate Change report set out a best estimate of 3 °C, with a 66 percent chance that the true answer lies be- tween 2 °C and 4.5 °C, and a slight but real possibility of more than 10 °C of warming.
Now, Andreas Schmittner of Oregon State University, and col- leagues, have produced a more precise answer by using a more complete temperature recon- struction of the last ice age — 21,000 years ago — than was pre- viously available. Their warming estimate is 2.3 °C, with a 66 per- cent chance the answer lies be- tween 1.7 °C and 2.6 °C. More than 6 °C of warming, the researchers conclude, would be implausible.
The latest estimate doesn’t fully cover the impact of ice sheets, vegetation or clouds on climate sensitivity, so the num- bers shouldn’t be taken as defin- itive, the researchers caution.
—Nicola Jones, Nature Climate Change
■■ Science doi: 10.1126/ science.1203513 (2011)
cARBON STORAGE
When peat dries peatlands locK away the large quantities of carbon that build up in these water-saturated environments owing to the pres- ence of phenolic compounds, which inhibit microbial decom- position. Phenolic concentra- tions remain high in peatlands because anoxic conditions limit the activity of the enzyme re- sponsible for their breakdown. However, droughts introduce ox- ygen into these systems, and the frequency of these events is increasing.
Nathalie Fenner and Chris Freeman of the Wolfson Peatland Carbon Capture Laboratory at Bangor University in Wales, UK, used in vitro manipulations, me- socosm experiments and field observations to examine the im- pact of drought on peatland carbon.
They found that drought stimulates bacterial growth and activity of the enzyme phenol oxidase, reducing the concen- tration of phenolic compounds in peat. This further stimulates microbial growth, causing the breakdown of organic matter and the release of carbon di- oxide. Furthermore, they show that re-wetting the peat acceler- ates carbon losses to the atmo- sphere, owing to drought-in- duced increases in nutrient and labile carbon levels, which raise pH and stimulate anaerobic de- composition. These findings suggest that severe drought, and subsequent re-wetting,
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could destabilize peatland carbon stocks.
—Alastair Brown, Nature Climate Change
■■ Nature Geosci. doi: 10.1038/ ngeo1323 (2011)
BIOlOGY
Growing up too fast foR ectotheRms — cold- blooded animals, including rep- tiles and amphibians, which cannot regulate their tempera- ture through their own metabo- lism — environmental tempera- ture changes “literally change the pace of life,” according to We- nyun Zuo, of the University of New Mexico in Albuquerque, and colleagues.
Ectotherms develop from in- fancy to adulthood more quickly in warmer conditions, and in- crease their body mass faster too. Most ectotherms follow a temperature-size rule, whereby the warmer the temperature, the smaller the animal is at maturity. But for about 15 percent of spe- cies, the reverse holds: the warmer it is, the larger they get.
Zuo’s team explains this oddity with a simple mathemat- ical model, in which the rate of biomass accumulation and the pace of maturity have different temperature dependences. The usual size rule applies for those animals in which temperature
has a stronger affect on develop- ment rate than on body mass ac- cumulation. The model shows that these animals not only ma- ture more quickly at warmer temperatures, but also use less energy to do so, giving them an evolutionary advantage in most conditions. Their model could be used to predict the effects of cli- mate change on various species’ body sizes, the authors say.
—Nicola Jones, Nature Climate Change
■■ Proc. R. Soc. B doi: 10.1098/ rspb.2011.2000 (2011)
clIMATE chANGE
Winter breezy, dry and dusty high-latitude climate
changes can have serious conse- quences for East Asia. Previous studies have found that, for ex- ample, changes in westerly winds and the Mongolian high- pressure system are the reasons behind the increasing episodes of desertification, sandstorms and “muddy rain” in China.
A new study led by Youbin Sun at the Chinese Academy of Sciences in Xi’an has now found that rising temperatures in Greenland may strengthen winter monsoons, promote dust storms and reduce summer pre- cipitation in East Asia.
The researchers performed grain-size analysis and optical dating on loess soils obtained from Jingyuan County, Ningxia, and Gulang County, Gangsu — both located in the depocenter of modern dust storms. Because the grain size of loess soil re- flects changes in winter mon- soon strength, they were able to reconstruct a record of winter monsoon intensity over the past 60,000 years.
The researchers found strong correlations between East Asian winter monsoon, Greenland ice- core and Chinese cave records.
They suggest that temperatures in Greenland may have a direct effect on the winter monsoon in- tensity, dust grain size and summer monsoon precipitation over East Asia. If this is true, rising temperatures in Green- land are likely to bring in- creasing episodes of natural disasters.
—Felix Cheung, Nature China
■■ Nature Geosci. doi:10.1038/ngeo1326 (2011)
clIMATE chANGE
The growth of dying seas
oxygen-depRived dead
zones in coastal waters around the world have expanded expo- nentially since the 1960s and are likely to increase further in a warming climate.
Markus Meier of the Swedish Meteorological and Hydrolog- ical Institute in Norrköping and his colleagues used a group of physical–biogeochemical models, driven by data from re- gional climate models, to project the effects of climate change and changes in nutrient cycles on ox- ygen conditions in the Baltic Sea.
Most scenarios suggested that oxygen-depleted zones at the bottom of the sea would ex- pand by the end of the century. Driving factors include rising nutrient input from river runoff; reduced oxygen flux from the at-
Salamanders and other ectotherms develop faster in a warmer world.
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Ocean dead zone, featuring a red algal bloom, off the coast of San Diego, Calif.
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mosphere to the ocean; and in- creased oxygen consumption by surface-level organisms that are fed by the boost in nutrients. Similar changes can be expected for coastal oceans worldwide, the authors say.
—Quirin Schiermeier, Nature
■■ Geophys. Res. Lett. doi: 10.1029/2011GL049929 (2011)
clIMATE
Precession control maRine sediment analyses suggest that over the past 400,000 years, the hydrological cycle over the Western Pacific warm pool was controlled by local incoming solar radiation.
Kazuyo Tachikawa and col- leagues at Aix-Marseille Univer- sity, France, determined the geo- chemistry of marine sediments and associated fossils in a core collected from the northern coast of Papua New Guinea. Using the abundance of ele- ments typically found in the rocks of the island, they recon- structed river run-off, and hence precipitation, over the past four glacial–interglacial cycles. Some- what surprisingly, precipitation intensity was seemingly unre- lated to the glacial cycles. In- stead, changes in rainfall were closely linked with the preces- sion of the Earth’s orbit, which strongly influences insolation in
the tropics on a 23,000-year cycle.
Records in other parts of the warm pool that do show glacial– interglacial shifts in precipita- tion could reflect the effects of glacial reduction of sea level, which eliminated the shallow seas that serve as a moisture source to the neighboring islands.
—Alicia Newton, Nature Geoscience
■■ Quat. Sci. Rev. doi: 10.1016/ j.quascirev.2011.09.016 (2011)
ATMOSphERIc ScIENcE
Windy future climate change is antici- pated to lead to more frequent wind storms in Europe with an associated boost in the incidence of dangerous sea conditions, coastal flooding and property damage. Some modeling studies indicate that an increasing storm trend may already be de- tectable in observational re- cords, but robust evidence has been missing.
Markus Donat, of the Climate Change Research Centre at Uni- versity of New South Wales, Sydney, and his co-workers used a newly developed atmospheric reconstruction for the period 1871–2008 to calculate two dif- ferent measures of storminess — storm frequency and local wind speeds — for six regions across Europe.
In addition to pronounced decadal-scale variability, the re- searchers found a distinct in- crease in wind-storm activity to- wards the end of the twentieth century, which was particularly clear in the North Sea and Baltic Sea regions. It is not yet clear whether this trend can be attrib- uted to climate change.
—Alastair Brown, Nature Climate Change
■■ Geophys. Res. Lett. doi: 10.1029/2011GL047995 (2011)
BIOFUEl
Fuel or housing?
substantial incReases in corn production will be required in the United States to meet the 2020 biofuel targets set by the 2007 Energy Independence and Security Act. Initially these tar- gets will consist entirely of corn- starch-based fuels, and the pro- ductive Midwest is likely to bear the brunt of these policy goals.
Megan Mehaffey and her col- leagues at the US Environmental Protection Agency investigated the landscape changes required to meet these biofuel targets. Their model suggests that 25 million acres of farmland in the American Midwest will need to switch from crop rotation to full- time corn production, with sev- eral regions increasing full-time corn production by more than 50 percent. At the same time, urban growth by 2020 is expected to cover more than seven million acres of farmland, potentially pushing corn production into smaller, more intensive areas or onto lower-quality land.
The model indicates where landscape changes are likely to occur, and should help policy- makers to evaluate the trade-offs between economic benefits and ecosystem services offered by dif- ferent land-management options.
—Alastair Brown, Nature Climate Change
■■ Ecol. Soc. Am. doi: 10.1890/10-1573.1 (2011)
Precession of earth.
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Cornfields outside Chicago.
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ADApTATION
Coffee futures in may 2008, tropical storm Alma struck Costa Rica bringing floods and landslides that caused misery to thousands, loss of croplands and US$35 million in damages.
A few months later, Francisco Alpizar of the Environment for Development Centre in Turri- alba, Costa Rica, and his col- leagues investigated around 200 coffee farmers’ attitudes towards investing in adaptation mea- sures to prevent future losses. In an experiment, 95 percent of farmers in the Tarrazu valley, which had been badly hit by Alma, told the researchers that
they would invest in adaptation if there was a 10 percent chance of being hit by an extreme weather event. This dropped to
77 percent if there was a 5 per- cent chance and 31 percent if there was just a 1 percent chance. When the farmers weren’t told what their risk was, half of those who had said that they wouldn’t invest in adapta- tion at a 5 percent risk hedged their bets and decided to invest.
When neighboring farmers of differing risk levels were grouped, and told they could pool their resources and share adaptation costs, 69 percent of the groups said they would in- vest, irrespective of their indi- vidual risk.
—Monica Contestabile, Nature Climate Change
■■ Ecol. Econ. doi: 10.1016/ j.ecolecon.2011.07.004 (2011)
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