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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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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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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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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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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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Ecological Restoration in the Light of Ecological History
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Ecological history plays many roles in ecological restoration, most notably as a tool to identify and
characterize appropriate targets for restoration efforts. However, ecological history also reveals deep human
imprints on many ecological systems and indicates that secular climate change has kept many targets
moving at centennial to millennial time scales. Past and ongoing environmental changes ensure that many
historical restoration targets will be unsustainable in the coming decades. Ecological restoration efforts
should aim to conserve and restore historical ecosystems where viable, while simultaneously preparing to
design or steer emerging novel ecosystems to ensure maintenance of ecological goods and services.
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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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A Determination of the Cloud Feedback from Climate Variations over the Past Decade
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Estimates of Earth's climate sensitivity are uncertain, largely because of uncertainty in the
long-term cloud feedback. I estimated the magnitude of the cloud feedback in response to short-term
climate variations by analyzing the top-of-atmosphere radiation budget from March 2000 to February
2010. Over this period, the short-term cloud feedback had a magnitude of 0.54 T 0.74 (2s) watts
per square meter per kelvin, meaning that it is likely positive. A small negative feedback is possible,
but one large enough to cancel the climate’s positive feedbacks is not supported by these observations.
Both long- and short-wave components of short-term cloud feedback are also likely positive.
Calculations of short-term cloud feedback in climate models yield a similar feedback. I find no
correlation in the models between the short- and long-term cloud feedbacks.
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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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Beyond Predictions: Biodiversity Conservation in a Changing Climate
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Climate change is predicted to become a major threat to biodiversity in the 21st century,
but accurate predictions and effective solutions have proved difficult to formulate. Alarming
predictions have come from a rather narrow methodological base, but a new, integrated science
of climate-change biodiversity assessment is emerging, based on multiple sources and
approaches. Drawing on evidence from paleoecological observations, recent phenological and
microevolutionary responses, experiments, and computational models, we review the insights that
different approaches bring to anticipating and managing the biodiversity consequences of
climate change, including the extent of species’ natural resilience. We introduce a framework
that uses information from different sources to identify vulnerability and to support the design of
conservation responses. Although much of the information reviewed is on species, our framework
and conclusions are also applicable to ecosystems, habitats, ecological communities, and
genetic diversity, whether terrestrial, marine, or fresh water.
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