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The 2010 Amazon Drought
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Several global circulation models (GCMs)
project an increase in the frequency and
severity of drought events affecting the
Amazon region as a consequence of anthropogenic
greenhouse gas emissions (1). The proximate
cause is twofold, increasing Pacific sea surface
temperatures (SSTs), which may intensify El Niño
Southern Oscillation events and associated periodic
Amazon droughts, and an increase in the frequency
of historically rarer droughts associated with
high Atlantic SSTs and northwest displacement of
the intertropical convergence zone (1, 2). Such
droughts may lead to a loss of some Amazon forests,
which would accelerate climate change (3).
In 2005, a major Atlantic SST–associated drought
occurred, identified as a 1-in-100-year event (2).
Here, we report on a second drought in 2010, when
Atlantic SSTs were again high.
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Time to Adapt to a Warming World, But Where’s the Science?
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With dangerous global warming seemingly inevitable, users of climate information—
from water utilities to international aid workers—are turning to climate scientists for
guidance. But usable knowledge is in short supply
VOL 334 SCIENCE
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Global Resilience of Tropical Forest and Savanna to Critical Transitions
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It has been suggested that tropical forest and savanna could represent alternative stable states,
implying critical transitions at tipping points in response to altered climate or other drivers.
So far, evidence for this idea has remained elusive, and integrated climate models assume smooth
vegetation responses. We analyzed data on the distribution of tree cover in Africa, Australia,
and South America to reveal strong evidence for the existence of three distinct attractors:
forest, savanna, and a treeless state. Empirical reconstruction of the basins of attraction indicates
that the resilience of the states varies in a universal way with precipitation. These results allow
the identification of regions where forest or savanna may most easily tip into an alternative
state, and they pave the way to a new generation of coupled climate models.
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Modeling Effects of Environmental Change on Wolf Population Dynamics, Trait Evolution, and Life History
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Environmental change has been observed to generate simultaneous responses in population dynamics,
life history, gene frequencies, and morphology in a number of species. But how common are such
eco-evolutionary responses to environmental change likely to be? Are they inevitable, or do they
require a specific type of change? Can we accurately predict eco-evolutionary responses? We
address these questions using theory and data from the study of Yellowstone wolves. We show that
environmental change is expected to generate eco-evolutionary change, that changes in the
average environment will affect wolves to a greater extent than changes in how variable it is, and
that accurate prediction of the consequences of environmental change will probably prove elusive.
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Stationarity Is Dead: Whither Water Management?
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Climate change undermines a basic assumption
that historically has facilitated management of
water supplies, demands, and risks.
SCIENCE VOL 319
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Reducing Greenhouse Gas Emissions from Deforestation and ForestDegradation: Global Land-Use Implications
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Recent climate talks in Bali have made progress toward action on deforestation and forest degradation
in developing countries, within the anticipated post-Kyoto emissions reduction agreements. As a result
of such action, many forests will be better protected, but some land-use change will be displaced to
other locations. The demonstration phase launched at Bali offers an opportunity to examine potential
outcomes for biodiversity and ecosystem services. Research will be needed into selection of priority
areas for reducing emissions from deforestation and forest degradation to deliver multiple benefits,
on-the-ground methods to best ensure these benefits, and minimization of displaced land-use change
into nontarget countries and ecosystems, including through revised conservation investments
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Warming Up Food Webs
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How do predator-prey interactions influence Warming Up Food Webs ecosystem responses to climate change?
VOL 323 SCIENCE
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Megafaunal Decline and Fall
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Declines in North American megafauna
populations began before the Clovis period
and were the cause, not the result, of
vegetation changes and increased fires.
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Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America
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Although the North American megafaunal extinctions and the formation of novel plant communities are
well-known features of the last deglaciation, the causal relationships between these phenomena are
unclear. Using the dung fungus Sporormiella and other paleoecological proxies from Appleman Lake,
Indiana, and several New York sites, we established that the megafaunal decline closely preceded
enhanced fire regimes and the development of plant communities that have no modern analogs. The loss
of keystone megaherbivores may thus have altered ecosystem structure and function by the release of
palatable hardwoods from herbivory pressure and by fuel accumulation. Megafaunal populations
collapsed from 14,800 to 13,700 years ago, well before the final extinctions and during the BøllingAllerød
warm period. Human impacts remain plausible, but the decline predates Younger Dryas cooling
and the extraterrestrial impact event proposed to have occurred 12,900 years ago.
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The Last Glacial Maximum
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We used 5704 14C, 10Be, and 3
He ages that span the interval from 10,000 to 50,000 years ago
(10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global
ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions
occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern
summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all
ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in
these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an
increase in northern summer insolation, providing the source for an abrupt rise in sea level. The
onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent
with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.
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