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Why Is Climate Sensitivity So Unpredictable?
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Uncertainties in projections of future climate change have not lessened substantially in past
decades. Both models and observations yield broad probability distributions for long-term
increases in global mean temperature expected from the doubling of atmospheric carbon dioxide,
with small but finite probabilities of very large increases. We show that the shape of these
probability distributions is an inevitable and general consequence of the nature of the climate
system, and we derive a simple analytic form for the shape that fits recent published distributions
very well. We show that the breadth of the distribution and, in particular, the probability of
large temperature increases are relatively insensitive to decreases in uncertainties associated with
the underlying climate processes.
VOL 318 26 OCTOBER 2007
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Volcanic cause of catastrophe
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From the timing, it looks as if an episode of marked oceanic oxygen
deficiency during the Cretaceous was the result of undersea volcanism.
Studies of such events are relevant to the warming world of today.
NATURE|Vol 454|17 July 2008
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Are we in the midst of the sixth mass extinction? A view from the world of amphibians
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Many scientists argue that we are either entering or in the midst
of the sixth great mass extinction. Intense human pressure, both
direct and indirect, is having profound effects on natural environments.
The amphibians—frogs, salamanders, and caecilians—may
be the only major group currently at risk globally. A detailed
worldwide assessment and subsequent updates show that onethird
or more of the 6,300 species are threatened with extinction.
This trend is likely to accelerate because most amphibians occur in
the tropics and have small geographic ranges that make them
susceptible to extinction. The increasing pressure from habitat
destruction and climate change is likely to have major impacts on
narrowly adapted and distributed species. We show that
salamanders on tropical mountains are particularly at risk. A new
and significant threat to amphibians is a virulent, emerging infectious
disease, chytridiomycosis, which appears to be globally
distributed, and its effects may be exacerbated by global warming.
This disease, which is caused by a fungal pathogen and implicated
in serious declines and extinctions of >200 species of amphibians,
poses the greatest threat to biodiversity of any known disease. Our
data for frogs in the Sierra Nevada of California show that the
fungus is having a devastating impact on native species, already
weakened by the effects of pollution and introduced predators. A
general message from amphibians is that we may have little time
to stave off a potential mass extinction.
11466–11473 PNAS August 12, 2008 vol. 105 suppl. 1
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Phylogenetic patterns of species loss in Thoreau’s woods are driven by climate change
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Climate change has led to major changes in the phenology (the
timing of seasonal activities, such as flowering) of some species but
not others. The extent to which flowering-time response to temperature
is shared among closely related species might have
important consequences for community-wide patterns of species
loss under rapid climate change. Henry David Thoreau initiated a
dataset of the Concord, Massachusetts, flora that spans !150 years
and provides information on changes in species abundance and
flowering time. When these data are analyzed in a phylogenetic
context, they indicate that change in abundance is strongly correlated
with flowering-time response. Species that do not respond to
temperature have decreased greatly in abundance, and include
among others anemones and buttercups [Ranunculaceae pro parte
(p.p.)], asters and campanulas (Asterales), bluets (Rubiaceae p.p.),
bladderworts (Lentibulariaceae), dogwoods (Cornaceae), lilies (Liliales),
mints (Lamiaceae p.p.), orchids (Orchidaceae), roses (Rosaceae
p.p.), saxifrages (Saxifragales), and violets (Malpighiales).
Because flowering-time response traits are shared among closely
related species, our findings suggest that climate change has
affected and will likely continue to shape the phylogenetically
biased pattern of species loss in Thoreau’s woods
PNAS ! November 4, 2008 ! vol. 105 ! no. 44 ! 17029–17033
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A westward extension of the warm pool leads to a westward extension of the Walker circulation, drying eastern Africa
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Observations and simulations link anthropogenicgreenhouse and aerosol emissions with rapidly
increasing Indian Ocean sea surface temperatures (SSTs). Over the past 60 years, the Indian Ocean warmed two to three times faster than the central tropical Pacific, extending the tropical warm pool to the west by *40 longitude ([4,000 km). This propensity toward rapid warming in the Indian Ocean has been the dominant mode of interannual variability among SSTs throughout the tropical Indian and Pacific Oceans (55E–140W) since at least 1948, explaining more variance than anomalies associated with the El Nin˜o-Southern Oscillation (ENSO). In the atmosphere, the primary mode of variability has been a corresponding trend
toward greatly increased convection and precipitation over the tropical Indian Ocean. The temperature and rainfall increases in this region have produced a westward extension of the western, ascending branch of the atmospheric Walker circulation. Diabatic heating due to increased mid-tropospheric water vapor condensation elicits a westward atmospheric response that sends an easterly flow of dry air aloft toward eastern Africa. In recent decades (1980–2009), this response has suppressed convection over tropical eastern Africa, decreasing precipitation during the ‘long-rains’ season of March–June. This trend toward drought contrasts with projections of increased rainfall in eastern Africa and more ‘El Nin˜o-like’ conditions globally by the Intergovernmental Panel on Climate Change. Increased Indian Ocean SSTs appear likely to continue to strongly modulate the Warm Pool circulation, reducing precipitation in eastern Africa, regardless of whether the projected trend in ENSO is realized. These results have important food security implications,
informing agricultural development, environmental conservation, and water resource planning.
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Ecological responses to recent climate change
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There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible.
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Predicting satellite-derived patterns of large-scale disturbances in forests of the Pacific Northwest Region in response to recent climatic variation
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Across the Pacific Northwest, the climate between 1950 and 1975 was exceptionally cool and wet compared
with more recent conditions (1995–2005). We reasoned that the changes in climate could result in expanded
outbreaks of insects, diseases, and fire. To test this premise, we first modeled monthly variation in photosynthesis
and growth of the most widely distributed species, Douglas-fir (Pseudotsuga menziesii), using a
process-based model (3-PG) for the two periods. To compare with remotely sensed variables, we converted
modeled growth potential into maximum leaf area index (LAImax), which was predicted to range from 1 to 9
across the region. On most sites, varying soil moisture storage capacity (θcap) from 200 to 300 mm while
holding soil fertility constant, made slight but insignificant difference in simulated LAImax patterns. Both
values of θcap correlated well with LAI estimates acquired from NASA's MODIS satellites in June, 2005
(r2= 0.7). To evaluate where 15 coniferous tree species might be prone to wide-scale disturbance, we used
climatically-driven decision-tree models, calibrated in the 1950–1975 period, to identify vulnerable areas
in 1995–2005. We stratified predictions within 34 recognized ecoregions and compared these results with
large-scale disturbances recorded on MODIS imagery acquired between 2005 and 2009. The correlation
between the percent of species judged as vulnerable within each ecoregion and the percent of forested
areas recorded as disturbed with a MODIS-derived Global Disturbance Index was linear and accounted for
65 to 73% of the observed variation, depending on whether or not disturbance by fire was excluded from
the analysis. Based on climate projections through the rest of the rest of the 21st century, we expect continued
high levels of disturbance in ecoregions located beyond the climatically buffering influence of the Pacific
Ocean.
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How Much More Rain Will Global Warming Bring?
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Climate models and satellite observations both indicate that the total amount of water in the
atmosphere will increase at a rate of 7% per kelvin of surface warming. However, the climate
models predict that global precipitation will increase at a much slower rate of 1 to 3% per kelvin. A
recent analysis of satellite observations does not support this prediction of a muted response of
precipitation to global warming. Rather, the observations suggest that precipitation and total
atmospheric water have increased at about the same rate over the past two decades.
SCIENCE VOL 317 13 JULY 2007
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Slowly Warming
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A chart about global Warming
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Spatial patterns and policy implications for residential water use
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The front yard makes a powerful visual statement about the
occupants of the residence. As visible statements, yards are likely
to induce a behavioral response on the part of neighboring
residents. As an example, residents may strive to keep their
yard as green and lush as their neighbors. For Kelowna, British
Columbia, a highly significant positive spatial lag for summer
water use implies some degree of spatial emulation in water using
behavior. Other variables such as lot size, building size, assessed
value, presence of a pool, etc. impact on water use as expected. The
presence of a spatial lag implies a spatial multiplier for water
saving innovations. If local water managers and policy makers can
influence the spatial pattern of water saving innovations, they may be
able to increase the size of the multiplier effect. Similar spatial policies
may also be applicable to other socially influenced behaviors that
leave a spatial signature, such as protecting ecologically significant
habitats in urban areas
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