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May 30, 2007
RESEARCH FINDS
THAT EARTH'S CLIMATE IS APPROACHING 'DANGEROUS' POINT
NASA
and Columbia University Earth
Institute research finds that human-made greenhouse gases have brought
the
Earth’s climate close to critical tipping points, with
potentially dangerous
consequences for the planet.
From
a combination of climate
models, satellite data, and paleoclimate records the scientists
conclude that
the West Antarctic ice sheet, Arctic ice cover, and regions providing
fresh
water sources and species habitat are under threat from continued
global warming.
The research appears in the current issue of Atmospheric
Chemistry and Physics.
Tipping points can occur during climate change when the climate reaches
a state
such that strong amplifying feedbacks are activated by only moderate
additional
warming. This study finds that global warming of 0.6ºC in the
past 30 years has
been driven mainly by increasing greenhouse gases, and only moderate
additional
climate forcing is likely to set in motion disintegration of the West
Antarctic
ice sheet and Arctic sea ice. Amplifying feedbacks include increased
absorption
of sunlight as melting exposes darker surfaces and speedup of iceberg
discharge
as the warming ocean melts ice shelves that otherwise inhibit ice flow.
The researchers used data on earlier warm periods in Earth’s
history to
estimate climate impacts as a function of global temperature, climate
models to
simulate global warming, and satellite data to verify ongoing changes.
Lead
author James Hansen, NASA Goddard Institute for Space Studies, New
York, concludes:
"If global emissions of carbon dioxide continue to rise at the rate of
the
past decade, this research shows that there will be disastrous effects,
including increasingly rapid sea level rise, increased frequency of
droughts
and floods, and increased stress on wildlife and plants due to rapidly
shifting
climate zones."
The
researchers also investigate
what would be needed to avert large climate change, thus helping define
practical implications of the United Nations Framework Convention on
Climate
Change. That treaty, signed in 1992 by the United States
and almost all
nations of the world, has the goal to stabilize atmospheric greenhouse
gases
"at a level that prevents dangerous human-made interference with the
climate system."
Based on climate model studies and the history of the Earth the authors
conclude that additional global warming of about 1ºC
(1.8ºF) or more, above
global temperature in 2000, is likely to be dangerous. In turn, the
temperature
limit has implications for atmospheric carbon dioxide (CO2), which has
already
increased from the pre-industrial level of 280 parts per million (ppm)
to 383
ppm today and is rising by about 2 ppm per year. According to study
co-author
Makiko Sato of Columbia’s Earth Institute, "the temperature
limit implies
that CO2 exceeding 450 ppm is almost surely dangerous, and the ceiling
may be
even lower."
The study also shows that the reduction of non-carbon dioxide forcings
such as
methane and black soot can offset some CO2 increase, but only to a
limited extent.
Hansen notes that "we probably need a full court press on both CO2
emission rates and non-CO2 forcings, to avoid tipping points and save
Arctic
sea ice and the West Antarctic ice sheet."
A computer model developed by the Goddard Institute was used to
simulate
climate from 1880 through today. The model included a more
comprehensive set of
natural and human-made climate forcings than previous studies,
including
changes in solar radiation, volcanic particles, human-made greenhouse
gases,
fine particles such as soot, the effect of the particles on clouds and
land
use. Extensive evaluation of the model's ability to simulate climate
change is
contained in a companion paper to be published in Climate
Dynamics.
The
authors use the model for
climate simulations of the 21st century using both 'business-as-usual'
growth
of greenhouse gas emissions and an 'alternative scenario' in which
emissions
decrease slowly in the next few decades and then rapidly to achieve
stabilization of atmospheric CO2 amount by the end of the century.
Climate
changes are so large with 'business-as-usual', with additional global
warming
of 2-3ºC (3.6-5.4ºF) that Hansen concludes
"'business-as-usual' would be a
guarantee of global and regional disasters."
However, the study finds much less severe climate change –
one-quarter to
one-third that of the "business-as-usual" scenario – when
greenhouse
gas emissions follow the alternative scenario. "Climate effects may
still
be substantial in the 'alternative scenario', but there is a better
chance to
adapt to the changes and find other ways to further reduce the climate
change," said Sato.
While the researchers say it is still possible to achieve the
"alternative
scenario," they note that significant actions will be required to do
so.
Emissions must begin to slow soon. "With another decade of
'business-as-usual' it becomes impractical to achieve the 'alternative
scenario' because of the energy infrastructure that would be in place"
says Hansen.
More
information and images:
http://www.nasa.gov/centers/goddard/news/topstory/2007/danger_point.html
http://www.nasa.gov/vision/earth/environment/danger_point.html
##
Contact:
Leslie McCarthy
NASA Goddard Institute for Space
Studies
212-678-5507
This text is
derived from:
http://www.nasa.gov/centers/goddard/news/topstory/2007/danger_point.html
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