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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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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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Climate Outlook Looking Much The Same, or Even Worse
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Climate scientists have been feverishly preparing analyses for inclusion in the fifth climate assessment report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) due out in 2013. At the meeting, they gave colleagues a peek at where climate science stands 5 years after their last push to inform the authoritative international evaluation . The climate models are bigger and more sophisticated
than ever, speakers reported, but they are yielding the same wide range of possible warming and precipitation changes as they did 5 years ago. But when polled on other areas of concern, researchers say they see more trouble ahead than the previous IPCC assessment had, though less than some scientists had feared
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The Global Extent and Determinants of Savanna and Forest as Alternative Biome States
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Theoretically, fire–tree cover feedbacks can maintain savanna and forest as alternative stable states.
However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting
for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is
globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to
2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire
differentiates between savanna and forest. These may be alternative states over large areas, including
parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to
fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.
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Navigating the Anthropocene: Improving Earth System Governance
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The United Nations conference in Rio de
Janeiro in June is an important opportunity
to improve the institutional framework
for sustainable development.
VOL 335 SCIENCE
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Impacts of Biodiversity Loss
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How much diversity is needed to maintain
the productivity of ecosystems?
VOL 336 SCIENCE
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Generic Indicators for Loss of Resilience Before a Tipping Point Leading to Population Collapse
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Theory predicts that the approach of catastrophic thresholds in natural systems (e.g., ecosystems,
the climate) may result in an increasingly slow recovery from small perturbations, a phenomenon
called critical slowing down. We used replicate laboratory populations of the budding yeast
Saccharomyces cerevisiae for direct observation of critical slowing down before population
collapse. We mapped the bifurcation diagram experimentally and found that the populations
became more vulnerable to disturbance closer to the tipping point. Fluctuations of population
density increased in size and duration near the tipping point, in agreement with the theory.
Our results suggest that indicators of critical slowing down can provide advance warning of
catastrophic thresholds and loss of resilience in a variety of dynamical systems.
SCIENCE VOL 336 1
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Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000
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Fundamental thermodynamics and climate models suggest that dry regions will become drier
and wet regions will become wetter in response to warming. Efforts to detect this long-term
response in sparse surface observations of rainfall and evaporation remain ambiguous. We show
that ocean salinity patterns express an identifiable fingerprint of an intensifying water cycle.
Our 50-year observed global surface salinity changes, combined with changes from global climate
models, present robust evidence of an intensified global water cycle at a rate of 8 T 5% per degree
of surface warming. This rate is double the response projected by current-generation climate
models and suggests that a substantial (16 to 24%) intensification of the global water cycle will
occur in a future 2° to 3° warmer world.
SCIENCE VOL 336
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The Greenhouse Is Making the Water-Poor Even Poorer
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How bad will global warming get? The question
has long been cast in terms of how hot
the world will get. But perhaps more important
to the planet’s inhabitants will be how
much rising greenhouse gases crank up the
water cycle. Theory and models predict that
a strengthening greenhouse will increase
precipitation where it is already relatively
high—tropical rain forests, for example—
and decrease it where it is already low, as in
the subtropics.
SCIENCE VOL 336 27 APRIL 2012
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Plant Species Richness and Ecosystem Multifunctionality in Global Drylands
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Experiments suggest that biodiversity enhances the ability of ecosystems to maintain multiple
functions, such as carbon storage, productivity, and the buildup of nutrient pools (multifunctionality).
However, the relationship between biodiversity and multifunctionality has never been assessed globally
in natural ecosystems. We report here on a global empirical study relating plant species richness and
abiotic factors to multifunctionality in drylands, which collectively cover 41% of Earth’s land surface
and support over 38% of the human population. Multifunctionality was positively and significantly
related to species richness. The best-fitting models accounted for over 55% of the variation in
multifunctionality and always included species richness as a predictor variable. Our results suggest
that the preservation of plant biodiversity is crucial to buffer negative effects of climate change and
desertification in drylands.
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