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Lance Olsen
SCIENCE www.sciencemag.org
R E P O R TS
13 AUGUST 2004 VOL 305
More Intense,More Frequent,and Longer Lasting Heat Waves in the 21st Century
Gerald A.Meehl and Claudia Tebaldi
ABSTRACT : A global coupled climate model shows that there is a
distinct geographic pattern to future changes in heat waves. Model
results for areas of Europe and North America, associated with the
severe heat waves in Chicago in 1995 and Paris in 2003, show that
future heat waves in these areas will become more intense,more
frequent, and longer lasting in the second half of the 21st century.
Observations and the model show that present-day heat waves over
Europe and North America coincide with a speci fic atmospheric
circulation pattern that is intensi oed by ongoing increases in
greenhouse gases,I ndicating that it will produce more severe heat
waves in those regions in the future.
NATURE
November 17, 2005
Potential impacts of a warming climate on water availability in
snow-dominated regions
T. P. Barnett , J. C. Adam & D. P. Lettenmaier
ABSTRACT : All currently available climate models predict a
near-surface warming trend under the influence of rising levels of
greenhouse gases in the atmosphere. In addition to the direct effects
on climate - for example, on the frequency of heatwaves - this
increase in surface temperatures has important consequences for the
hydrological cycle, particularly in regions where water supply is
currently dominated by melting snow or ice. In a warmer world, less
winter precipitation falls as snow and the melting of winter snow
occurs earlier in spring. Even without any changes in precipitation
intensity, both of these effects lead to a shift in peak river runoff
to winter and early spring, away from summer and autumn when demand
is highest. Where storage capacities are not sufficient, much of the
winter runoff will immediately be lost to the oceans. With more than
one-sixth of the Earth's population relying on glaciers and seasonal
snow packs for their water supply, the consequences of these
hydrological changes for future water availability-predicted with
high confidence and already diagnosed in some regions-are likely to
be severe.
Proceedings of the National Academy of Sciences
2005;102;15144-15148; originally published online Oct 10, 2005; PNAS
Regional vegetation die-off in response
to global-change-type drought
David D. Breshears a,b , Neil S. Cobb c , Paul M. Rich d , Kevin P.
Price e,f , Craig D. Allen g , Randy G. Balice h , William H. Romme i
,
Global climate change is projected to yield increases in frequency
and intensity of drought occurring under warming temperatures (1-3),
referred to here as global-change-type drought. Protracted,
subcontinental drought in the midlatitudes is a complex response
driven in part by anomalies associated with oscillations in sea
surface temperature (2-4), which can include oscillations over
periods of decades or longer, such as those associated with the
Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation
(4), and shorter periods spanning several years, such as those
associated with the El Nin—o Southern Oscillation (3). Greenhouse gas
forcings are expected to alter these oceanic effects on drought
patterns (1-3). Indeed, the most recent protracted drought in
southwestern North America, spanning the beginning of the 2000
millennium, exhibited anomalous sea surface temperature patterns
consistent with projections of global change response (3). Protracted
drought can trigger large-scale landscape changes through vegetation
mor-tality from water stress (5, 6), sometimes associated with bark
beetle infestations (5), but the potential for regional to
subcontinental scale vegetation die-off under global-change-type
drought remains a pivotal uncertainty in projections of climate
change impacts (1, 7, 8). Of particular concern is regional-scale
mortality of overstory trees, which rapidly alters ecosystem type,
associated ecosystem properties, and land surface conditions for
decades.
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