Research finds that earth's climate is approaching "dangerous" point (Forwarded)

Leslie McCarthy
NASA Goddard Institute for Space Studies, New York May 30, 2007
212-678-5507

RELEASE: 07-30

RESEARCH FINDS THAT EARTH'S CLIMATE IS APPROACHING "DANGEROUS" POINT

NEW YORK -- 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
0.6 C 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 1 C (1.8 F) 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 2-3 C
(3.6-5.4 F) 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.

For related images and more information on this story, please visit on
the Web:
http://www.nasa.gov/vision/earth/env...ger_point.html

For more information about the NASA Goddard Institute for Space Studies
and the Columbia University Earth Institute visit:
http://www.giss.nasa.gov
http://www.earthinstitute.columbia.edu