Skip to main content
ad info

 
CNN.com  nature
CNN.com EUROPE:
Editions|myCNN|Video|Audio|News Brief|Free E-mail|Feedback  
 

Search


Search tips
NATURE
TOP STORIES

New hurdles hamper Galapagos oil spill cleanup

Senate panel backs Norton as interior chief

Insight, Prius lead the hybrid-powered fleet

New England moves to preserve red crab industries

Canadian smelters pledge to reduce toxic waste

Picture: Indonesia's Merapi volcano erupts

(MORE)

TOP STORIES

Up to 2,000 killed in India quake; fear of aftershocks spreads

Europe remembers the Holocaust

Plea to delay climate talks

Global BSE warning issued

(MORE)

 MARKETS    1613 GMT, 12/28
5217.4
-25.00
5160.1
+42.97
4624.58
+33.42

 
SPORTS

(MORE)

 All Scoreboards
WEATHER
European Forecast

 Or choose another Region:
EUROPE

WORLD

TECHNOLOGY

ENTERTAINMENT

  IN OTHER NEWS

U.S.

HEALTH

TRAVEL



(MORE HEADLINES)
*
EDITIONS:
CNN.com U.S.:

LOCAL LANGUAGES:


 DISCUSSION:
  CNN WEB SITES:
CNN Websites
 TIME INC. SITES:
 CNN NETWORKS:
Networks image
 SITE INFO:
 WEB SERVICES:

Clouds' role in global warming studied

The thickness and brightness of clouds influence how the planet heats and cools. Stratocumulus clouds were among those observed by researchers  
ENN



If the current warming trend continues, don't depend on low-level clouds to come to the Earth's rescue, according to NASA researchers.

A cloud's thickness and brightness (its ability to reflect sunlight) influences how the planet heats and cools. Clouds can act as a natural shield by reflecting sunlight back into space, creating cooler temperatures. And clouds can also wrap the skies like a blanket, sealing in warmth.

But what's unclear is how clouds will react when the Earth gets warmer, as it seems destined to do.

Some climatologists predict that a warmer atmosphere will evaporate more water, forming denser and brighter clouds that will reflect more sunlight back into space and cooling things off.

  MESSAGE BOARD
 

However, after three years of observations of low stratus, cumulus and stratocumulus clouds over land, Anthony Del Genio of NASA's Goddard Institute for Space Studies discovered that when air temperatures were higher, clouds were thinner and thus less capable of reflecting sunlight. These thinner clouds occurred regardless of weather conditions, season or time of day.

"The bottoms of the clouds rise with warmer temperatures, while the top of the cloud stays the same so the clouds become thinner," explained Del Genio. "When low clouds are present, warmer air flowing over land tends to be drier. As a parcel of dry air rises, it has to rise farther before it saturates with enough water to form the cloud base."

And, Del Genio disputes a theory that rising carbon dioxide levels would have only a slight impact on global temperatures because the theory doesn't take into account real world cloud behavior.

"The minimum amount of warming predicted by scientists - 3 degrees Fahrenheit - should be increased by at least 1 F as a result of the new findings," said Del Genio.

The current range of 21st century warming, according to the Intergovernmental Panel on Climate Change, is 3-8 F. The IPCC will release its updated global warming assessment early next year.

Del Genio studied more than 3,000 individual cloud "snapshots" collected between 1994 and 1997 at the Department of Energy's Atmospheric Radiation Measurement Southern Great Plains field station.

The whole-sky imager was one of the ground-based instruments used to record clouds  

Using a unique system of ground-based and satellite instruments, each snapshot recorded the air temperature, the height of the bottom and top of the cloud, and the amount of liquid water in the cloud. The more liquid water in a cloud and the thicker the cloud, the more opaque it is and the more sunlight it reflects.

"We concluded that over more than half of the world, when the temperatures were warmer, the low-level clouds reflect less sunlight, which will only exacerbate global warming," said Del Genio.

The link between cloud thinning and temperature was initially observed in 1992 over much of the world with long-term satellite observations. George Tselioudis, William Rossow and David Rind of the NASA Goddard Institute for Space Studies published the observation using the NASA-funded International Satellite Cloud Climatology Project database, a global composite of cloud observations from international weather satellites.

"In the larger context of the global warming debate I'd say we shouldn't look for clouds to get us out of this mess," said Del Genio. "This is just one aspect of clouds, but this is the part people assumed would make global warming less severe."

Del Genio and colleagues' research was published in the Oct. 1 issue of the American Meteorological Society's Journal of Climate.

Copyright 2000, Environmental News Network, All Rights Reserved




RELATED STORIES:
Report: Shorter lake and river ice seasons confirm global warming
September 7, 2000
NASA urges practical solutions for reducing greenhouse gases
August 16, 2000
Warmer tropical waters portend climate change
August 7, 2000
Global warming spells health warning
July 17, 2000

RELATED ENN STORIES:
Noctaluscent clouds (audio)
Soot eats clouds, turns up global thermostat
Polar clouds cause more ozone loss in Arctic
Atmospheric science quiz
Acid clouds destroy Arctic ozone, NASA says
U.S. will feel heat of global warming
Aerosols, clouds, climate get $25 million study

RELATED SITES:
Goddard Institute for Space Studies
Atmospheric Radiation Measurement Southern Great Plains field station.
American Meteorological Society's Journal of Climate
clouds
Intergovernmental Panel on Climate Change
global warming and the atmosphere

Note: Pages will open in a new browser window
External sites are not endorsed by CNN Interactive.

 Search   


Back to the top   © 2001 Cable News Network. All Rights Reserved.
Terms under which this service is provided to you.
Read our privacy guidelines.