yee@ames.arc.nasa.gov (Peter E. Yee) (02/07/89)
Charles Redmond Headquarters, Washington, D.C. February 3, 1989 Keith Henry Langley Research Center, Hampton, Va. RELEASE: 89-14 EFFECTS OF CLOUDS ON CLIMATE MEASURED BY NASA PROJECT The most accurate Earth radiation budget measurements ever made, provided by NASA's Earth Radiation Budget Experiment (ERBE) satellite, confirm that clouds result in a net cooling of the Earth. Previously, atmospheric scientists were divided on the impact of clouds on the Earth's temperature. These measurements serve as the baseline for climate modelers to determine whether clouds will partially offset or enhance a future warming of the Earth due to the greenhouse effect. The greenhouse effect is the term given to warming of the Earth's atmosphere and surface resulting from increased concentrations of gases, such as carbon dioxide, methane, nitrous oxide and chlorofluorocarbons. The major uncertainty in the current ability to assess the future impact of greenhouse gases is the effect of clouds. ERBE has given climate modelers some very specific numbers to test and validate their models. At any given time, clouds cover about 60 percent of the Earth. Wispy, high-altitude cirrus (ice) clouds generally tend to warm the surface. They reflect less solar energy back to space than stratus and cumulus (liquid water) clouds. Because they are so high in the atmosphere, ice clouds are more efficient at trapping the infrared heat energy emitted by the Earth and the atmosphere. Low-level water clouds not only shade the Earth's surface from the Sun's rays better than high- altitude ice clouds, they emit almost as much infrared radiation as a cloud-free Earth. The net effect of clouds on surface temperatures depends on how these different cloud types are distributed over the globe. The first of the three ERBE satellites was launched by the Space Shuttle Challenger in October 1984. National Oceanic and Atmospheric Administration (NOAA) weather satellites NOAA-9 and NOAA-10 launched in December 1984 and September 1986, respectively, also carried the ERBE instruments. ERBE provided the first opportunity to measure the three components of the Earth's radiation balance with identical instruments flying simultaneously on separate satellites. ERBE's instruments measured the solar radiation striking the Earth and the solar radiation reflected by the Earth. These two measurements determine how much solar energy is absorbed by the Earth. The absorbed solar radiation heats the Earth's surface. The infrared radiation emitted by the Earth and its atmosphere also is measured. This emitted radiation cools the surface of the Earth. The ERBE measurements indicate that in April 1985, clouds reflected back to space considerably more radiation than they trapped in the atmosphere and the surface. This loss of radiation due to the clouds is approximately equivalent to a 10 to 30 degrees F. decrease in the global surface temperature. Thus, barring changes in any other variables, the Earth would be about 20 degeees F. warmer without any cloud cover. In comparison, climate modelers believe that a doubling of carbon dioxide in the atmosphere would result in a warming of about 4 to 8 degrees F. Global warming would change circulation patterns, altering the climates and growing seasons of many regions over the globe. Significant warming also would melt large amounts of ice and snow in the polar regions, increasing the height of the world's oceans. Changes in global circulation patterns would also change the distribution of clouds over the globe. The ERBE data also revealed for the first time the regional distribution of cloud effects over the globe. Langley scientists Patrick Minnis and Edwin F. Harrison published the first paper in 1984 showing the regional cloud effects over part of the Earth. They used data from a weather satellite which only observed North and South America. The ERBE satellites viewed all of the Earth with sensors much more accurate than those normally carried on weather satellites. ERBE is the first step in NASA's long-term program for studying climate change and is both a national and international effort supported by other government agencies and universities. The ERBE satellite instruments were developed at Langley and the TRW Corporation, Redondo Beach, Calif. Langley is responsible for data analysis. ERBS was developed at NASA's Goddard Space Flight Center, Greenbelt, Md., and Ball Aerospace, Boulder, Colo. NOAA supplied the two weather satellites.
eli@spdcc.COM (Steve Elias) (02/07/89)
for more information on this topic, refer to Science, 6 Jan 1989. -- Steve Elias (eli@spdcc.com);((617 239 9406)) *funk() /* C, not lisp */