Decline in greenhouse gas emissions would reduce
sea-level rise, save Arctic Sea ice
Wednesday, April 15, 2009
The threat of global warming can still be greatly diminished if
nations cut emissions of heat-trapping greenhouse gases by 70
percent this century, according to a new analysis.
While global temperatures would rise, the most dangerous potential
aspects of climate change, including massive losses of Arctic sea
ice and permafrost and significant sea-level rise, could be
partially avoided.
The study, led by scientists at the National Center for Atmospheric
Research (NCAR), will be published next week in the American
Geophysical Union journal Geophysical Research Letters.
It was funded by the Department of Energy and the National Science
Foundation (NSF), NCAR's sponsor.
"This important study, when taken with similar efforts, will help
define a major challenge for society," says Cliff Jacobs of NSF's
Atmospheric Sciences Division.
"This research indicates that we can no longer avoid significant
warming during this century," says NCAR scientist Warren
Washington, the paper's lead author. "But if the world were to
implement this level of emission cuts, we could stabilize the
threat of climate change."
Average global temperatures have warmed by close to 1 degree
Celsius (almost 1.8 degrees Fahrenheit) since the pre-industrial
era. Much of the warming is due to human-produced emissions of
greenhouse gases, predominantly carbon dioxide.
This heat-trapping gas has increased from a pre-industrial level of
about 284 parts per million (ppm) in the atmosphere to more than
380 ppm today.
With research showing that additional warming of about 1 degree C
(1.8 F) may be the threshold for dangerous climate change, the
European Union has called for dramatic cuts in emissions of carbon
dioxide and other greenhouse gases. The U.S. Congress is also
debating the issue.
To examine the impact of such cuts on the world's climate,
Washington and his colleagues ran a series of global supercomputer
studies with the NCAR-based Community Climate System Model
(CCSM).
They assumed that carbon dioxide levels could be held to 450 ppm at
the end of this century.
That figure comes from the U.S. Climate Change Science Program,
which has cited 450 ppm as an attainable target if the world
quickly adapts conservation practices and new green technologies to
cut emissions dramatically.
In contrast, emissions are now on track to reach about 750 ppm by
2100 if unchecked.
The team's results showed that if carbon dioxide were held to 450
ppm, global temperatures would increase by 0.6 degrees Celsius
(about 1 F) above current readings by the end of the century.
In contrast, the study showed that temperatures would rise by
almost four times that amount, to 2.2 degrees Celsius (4 F) above
current readings, if emissions were allowed to continue on their
present course.
Holding carbon dioxide levels to 450 ppm would have other impacts,
according to the climate modeling study:
Sea-level rise due to thermal expansion as water temperatures
warmed would be 14 centimeters (about 5.5 inches) instead of 22
centimeters (8.7 inches). Significant additional sea-level rise
would be expected in either scenario from melting ice sheets and
glaciers.
Arctic ice in the summertime would shrink by about a quarter in
volume and stabilize by 2100, as opposed to shrinking at least
three-quarters and continuing to melt. Some research has suggested
the summertime ice will disappear altogether this century if
emissions continue on their current trajectory.
Arctic warming would be reduced by almost half, helping preserve
fisheries and populations of sea birds and Arctic mammals in such
regions as the northern Bering Sea.
Significant regional changes in precipitation, including decreased
precipitation in the U.S. Southwest and an increase in the U.S.
Northeast and Canada, would be cut in half if emissions were kept
to 450 ppm.
The climate system would stabilize by about 2100, instead of
continuing to warm.
The researchers used supercomputer simulations to compare a
business-as-usual scenario to one with dramatic cuts in carbon
dioxide emissions beginning in about a decade. The authors stressed
that they were not studying how such cuts could be achieved nor
advocating a particular policy.
"Our goal is to provide policymakers with appropriate research so
they can make informed decisions," Washington says.
"This study provides some hope that we can avoid the worst impacts
of climate change--if society can cut emissions substantially over
the next several decades and continue major cuts through the
century."
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National Science Foundation
Thanks to National Science Foundation for this article.
