Bowser
02-28-01, 11:23 AM
Press Release:
Goddard Space Flight Center, Greenbelt, Md. February 28, 2001
American Meteorological Society
Release No: 01-18
NATURAL "HEAT VENT" IN PACIFIC CLOUD COVER
COULD DIMINISH GREENHOUSE WARMING
The tropical Pacific Ocean may be able to open a "vent" in its
heat-trapping cirrus cloud cover and release enough energy into space
to significantly diminish the projected climate warming caused by a
buildup of greenhouse gases in the atmosphere.
If confirmed by further research, this newly discovered effect -
which is not seen in current climate prediction models - could
significantly reduce estimates of future climate warming. Scientists
from NASA's Goddard Space Flight Center in Greenbelt, Md., and the
Massachusetts Institute of Technology present their findings in the
March 2001 issue of the Bulletin of the American Meteorological
Society.
"High clouds over the western tropical Pacific Ocean seem to
systematically decrease when sea surface temperatures are higher,"
says Arthur Y. Hou of Goddard's Data Assimilation Office. Hou and
co-authors Ming-Dah Chou of Goddard's Climate and Radiation Branch
and Richard S. Lindzen of MIT analyzed satellite observations over
the vast ocean region, which stretches from Australia and Japan
nearly to the Hawaiian Islands.
The researchers compare this inverse relationship to the eye's iris,
which opens and closes to counter changes in light intensity. The
"adaptive infrared iris" of cirrus clouds opens and closes to permit
the release of infrared energy, thus resisting warmer tropical sea
surface temperatures, which occur naturally and are predicted to
increase as the result of climate warming.
The study compares detailed daily observations of cloud cover from
Japan's GMS-5 Geostationary Meteorological Satellite with sea surface
temperature data from the U. S. National Weather Service's National
Centers for Environmental Prediction over a 20-month period (January
1998 to August 1999). The researchers found that cumulus cloud towers
produced less cirrus clouds when they moved over warmer ocean
regions. For each degree Celsius rise in ocean surface temperature,
the ratio of cirrus cloud area to cumulus cloud area over the ocean
dropped 17-27 percent. The observed range of surface temperatures
beneath the clouds varied by 6.3 degrees Fahrenheit (3.5 degees C).
The authors propose that higher ocean surface temperatures directly
cause the decline in cirrus clouds by changing the dynamics of cloud
formation and rainfall. Cirrus clouds - high-altitude clouds of ice
crystals - typically form as a byproduct of the life cycle of cumulus
towers created by rising updrafts of heated, moist air. As these
cumulus convective clouds grow taller, cloud water droplets collide
and combine into raindrops and fall out of the cloud or continue to
rise until they freeze into ice crystals and form cirrus clouds.
"With warmer sea surface temperatures beneath the cloud, the
coalescence process that produces precipitation becomes more
efficient," explains Lindzen. "More of the cloud droplets form
raindrops and fewer are left in the cloud to form ice crystals. As a
result, the area of cirrus cloud is reduced."
Clouds play a critical and complicated role in regulating the
temperature of the Earth. Thick, bright, watery clouds like cumulus
shield the atmosphere from incoming solar radiation by reflecting
much of it back into space. Thin, icy cirrus clouds are poor
sunshields but very efficient insulators that trap energy rising from
the Earth's warmed surface. A decrease in cirrus cloud area would
have a cooling effect by allowing more heat energy, or infrared
radiation, to leave the planet.
If this "iris effect" is found to be a general process active in
tropical oceans around the world, the Earth may be much less
sensitive to the warming effects of such influences as rising
greenhouse gas concentrations in the atmosphere. The researchers
estimate that this effect could cut by two-thirds the projected
increase in global temperatures initiated by a doubling of carbon
dioxide in the atmosphere.
The American Meteorological Society is the nation's leading
professional society for scientists in the atmospheric, oceanic, and
related sciences.
-end-
Goddard Space Flight Center, Greenbelt, Md. February 28, 2001
American Meteorological Society
Release No: 01-18
NATURAL "HEAT VENT" IN PACIFIC CLOUD COVER
COULD DIMINISH GREENHOUSE WARMING
The tropical Pacific Ocean may be able to open a "vent" in its
heat-trapping cirrus cloud cover and release enough energy into space
to significantly diminish the projected climate warming caused by a
buildup of greenhouse gases in the atmosphere.
If confirmed by further research, this newly discovered effect -
which is not seen in current climate prediction models - could
significantly reduce estimates of future climate warming. Scientists
from NASA's Goddard Space Flight Center in Greenbelt, Md., and the
Massachusetts Institute of Technology present their findings in the
March 2001 issue of the Bulletin of the American Meteorological
Society.
"High clouds over the western tropical Pacific Ocean seem to
systematically decrease when sea surface temperatures are higher,"
says Arthur Y. Hou of Goddard's Data Assimilation Office. Hou and
co-authors Ming-Dah Chou of Goddard's Climate and Radiation Branch
and Richard S. Lindzen of MIT analyzed satellite observations over
the vast ocean region, which stretches from Australia and Japan
nearly to the Hawaiian Islands.
The researchers compare this inverse relationship to the eye's iris,
which opens and closes to counter changes in light intensity. The
"adaptive infrared iris" of cirrus clouds opens and closes to permit
the release of infrared energy, thus resisting warmer tropical sea
surface temperatures, which occur naturally and are predicted to
increase as the result of climate warming.
The study compares detailed daily observations of cloud cover from
Japan's GMS-5 Geostationary Meteorological Satellite with sea surface
temperature data from the U. S. National Weather Service's National
Centers for Environmental Prediction over a 20-month period (January
1998 to August 1999). The researchers found that cumulus cloud towers
produced less cirrus clouds when they moved over warmer ocean
regions. For each degree Celsius rise in ocean surface temperature,
the ratio of cirrus cloud area to cumulus cloud area over the ocean
dropped 17-27 percent. The observed range of surface temperatures
beneath the clouds varied by 6.3 degrees Fahrenheit (3.5 degees C).
The authors propose that higher ocean surface temperatures directly
cause the decline in cirrus clouds by changing the dynamics of cloud
formation and rainfall. Cirrus clouds - high-altitude clouds of ice
crystals - typically form as a byproduct of the life cycle of cumulus
towers created by rising updrafts of heated, moist air. As these
cumulus convective clouds grow taller, cloud water droplets collide
and combine into raindrops and fall out of the cloud or continue to
rise until they freeze into ice crystals and form cirrus clouds.
"With warmer sea surface temperatures beneath the cloud, the
coalescence process that produces precipitation becomes more
efficient," explains Lindzen. "More of the cloud droplets form
raindrops and fewer are left in the cloud to form ice crystals. As a
result, the area of cirrus cloud is reduced."
Clouds play a critical and complicated role in regulating the
temperature of the Earth. Thick, bright, watery clouds like cumulus
shield the atmosphere from incoming solar radiation by reflecting
much of it back into space. Thin, icy cirrus clouds are poor
sunshields but very efficient insulators that trap energy rising from
the Earth's warmed surface. A decrease in cirrus cloud area would
have a cooling effect by allowing more heat energy, or infrared
radiation, to leave the planet.
If this "iris effect" is found to be a general process active in
tropical oceans around the world, the Earth may be much less
sensitive to the warming effects of such influences as rising
greenhouse gas concentrations in the atmosphere. The researchers
estimate that this effect could cut by two-thirds the projected
increase in global temperatures initiated by a doubling of carbon
dioxide in the atmosphere.
The American Meteorological Society is the nation's leading
professional society for scientists in the atmospheric, oceanic, and
related sciences.
-end-