Carbon Dioxide Controls Earth's Temperature

[Henk Elegeert]

REPLY TO: D66 at nic.surfnet.nl

*Carbon Dioxide Controls Earth's
Temperature*<http://www.nasa.gov/topics/earth/features/co2-temperature.html>

"
 Water vapor and clouds are the major contributors to Earth's greenhouse
effect, but a new atmosphere-ocean climate modeling study shows that the
planet's temperature ultimately depends on the atmospheric level of carbon
dioxide.

The study, conducted by Andrew Lacis and colleagues at NASA's Goddard
Institute for Space Studies (GISS) in New York, examined the nature of
Earth's greenhouse effect and clarified the role that greenhouse gases and
clouds play in absorbing outgoing infrared radiation. Notably, the team
identified non-condensing greenhouse gases -- such as carbon dioxide,
methane, nitrous oxide, ozone, and chlorofluorocarbons -- as providing the
core support for the terrestrial greenhouse effect.

Without non-condensing greenhouse gases, water vapor and clouds would be
unable to provide the feedback mechanisms that amplify the greenhouse
effect. The study's results will be published Friday, Oct. 15 in Science.

A companion study led by GISS co-author Gavin Schmidt that has been accepted
for publication in the Journal of Geophysical Research shows that carbon
dioxide accounts for about 20 percent of the greenhouse effect, water vapor
and clouds together account for 75 percent, and minor gases and aerosols
make up the remaining five percent. However, it is the 25 percent
non-condensing greenhouse gas component, which includes carbon dioxide, that
is the key factor in sustaining Earth’s greenhouse effect. By this
accounting, carbon dioxide is responsible for 80 percent of the radiative
forcing that sustains the Earth’s greenhouse effect.

The climate forcing experiment described in Science was simple in design and
concept -- all of the non-condensing greenhouse gases and aerosols were
zeroed out, and the global climate model was run forward in time to see what
would happen to the greenhouse effect. Without the sustaining support by the
non-condensing greenhouse gases, Earth’s greenhouse effect collapsed as
water vapor quickly precipitated from the atmosphere, plunging the model
Earth into an icebound state -- a clear demonstration that water vapor,
although contributing 50 percent of the total greenhouse warming, acts as a
feedback process, and as such, cannot by itself uphold the Earth's
greenhouse effect.

"Our climate modeling simulation should be viewed as an experiment in
atmospheric physics, illustrating a cause and effect problem which allowed
us to gain a better understanding of the working mechanics of Earth’s
greenhouse effect, and enabled us to demonstrate the direct relationship
that exists between rising atmospheric carbon dioxide and rising global
temperature," Lacis said.

The study ties in to the geologic record in which carbon dioxide levels have
oscillated between approximately 180 parts per million during ice ages, and
about 280 parts per million during warmer interglacial periods. To provide
perspective to the nearly 1 C (1.8 F) increase in global temperature over
the past century, it is estimated that the global mean temperature
difference between the extremes of the ice age and interglacial periods is
only about 5 C (9 F).

"When carbon dioxide increases, more water vapor returns to the atmosphere.
This is what helped to melt the glaciers that once covered New York City,"
said co-author David Rind, of NASA's Goddard Institute for Space Studies.
"Today we are in uncharted territory as carbon dioxide approaches 390 parts
per million in what has been referred to as the 'superinterglacial.'"

"The bottom line is that atmospheric carbon dioxide acts as a thermostat in
regulating the temperature of Earth," Lacis said. "The Intergovernmental
Panel on Climate Change has fully documented the fact that industrial
activity is responsible for the rapidly increasing levels of atmospheric
carbon dioxide and other greenhouse gases. It is not surprising then that
global warming can be linked directly to the observed increase in
atmospheric carbon dioxide and to human industrial activity in general."

*Related Links:*

GISS Science Brief: The Thermostat that Controls Earth's
Temperature<http://www.giss.nasa.gov/research/briefs/lacis_01/>

GISS Science Brief: Taking the Measure of the Greenhouse
Effect<http://www.giss.nasa.gov/research/briefs/schmidt_05/>

NASA GISS: Andrew Lacis <http://www.giss.nasa.gov/staff/alacis.html>

NASA GISS: David Rind <http://www.giss.nasa.gov/staff/drind.html>

NASA GISS: Gavin Schmidt <http://www.giss.nasa.gov/staff/gschmidt/>

Water Vapor Confirmed as Major Player in Climate
Change<http://www.nasa.gov/topics/earth/features/vapor_warming.html>



Kathryn Hansen
NASA's Earth Science News Team
"

Nou, ben benieuwd ...

Henk Elegeert

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