Do clouds provide a greenhouse thermostat?Earth's oceans have a natural thermostat that -- at least for the present -- keeps their surface waters from warming above 32'C. Understanding that thermostat may be critical for predicting how the climate will change, but new research shows that the problem does not yield to a simple explanation. Last year, hope for a straightforward answer ran high. V Ramanathan and William Collins William Collins may refer to:
This week, however, a group of atmospheric researchers disputes the cirrus thermostat model. "Our contention is that clouds are really not the story," says Anthony D. Del Genio of NASA's Goddard Institute for Space Studies The NASA Goddard Institute for Space Studies (GISS), at Columbia University in New York City, is a component laboratory of NASA's Goddard Space Flight Center Earth-Sun Exploration Division and a unit of The Earth Institute at Columbia University. in New York City New York City: see New York, city. New York City City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S. a coauthor of the study led by Rong Fu of the University of California, Los Angeles UCLA comprises the College of Letters and Science (the primary undergraduate college), seven professional schools, and five professional Health Science schools. Since 2001, UCLA has enrolled over 33,000 total students, and that number is steadily rising. . They report their work in the July 30 NATURE. Ramanathan and Collins presented satellite data suggesting that cirrus clouds helped limit ocean temperatures in 1987, when an El Nino warming brewed in the equatorial Pacific. The data showed that as the sea surface warmed in the central and eastern equatorial Pacific, cirrus clouds reflected more sunlight back into space, cutting down the light reaching the ocean surface. Fu and her colleagues counter with evidence that sea surface temperatures Sea surface temperature (SST) is the water temperature at the surface. In practical terms, the exact meaning of "surface" will vary according to the measurement method used. do not control cirrus cloud formation. Using satellite data for the whole tropical Pacific, they find that cirrus clouds across this broad region remained nearly normal during the 1987 El Nino, even though sea surface temperatures rose by 2 [degrees] C to 3 [degrees] C through the area, says Del Genio. Looking at years without El Nino warmings, the researchers found enhancements in cirrus clouds even when ocean temperatures did not increase, indicating that some other factor controlled the cloud properties. If cirrus clouds don't cap ocean temperatures, evaporation may, suggest the researchers. Water evaporating from the ocean releases heat into the atmosphere, cooling off the sea surface, just as evaporating sweat chills a person's skin. Ocean circulation could also help regulate temperatures by carrying warm water away from the tropics tropics, also called tropical zone or torrid zone, all the land and water of the earth situated between the Tropic of Cancer at lat. 23 1-2°N and the Tropic of Capricorn at lat. 23 1-2°S. , Del Genio says. Ramanathan and Collins contend they are not through yet. Collins told SCIENCE NEWS that several groups have papers pending that contradict the conclusions of Fu and her co-workers. Part of the discrepancy arises because Fu's group looked at the entire tropics, effectively diminishing the importance of the El Nino warming near the equator, Collins says. The debate is important because the tropical Pacific has Earth's strongest greenhouse effect greenhouse effect: see global warming. greenhouse effect Warming of the Earth's surface and lower atmosphere caused by water vapour, carbon dioxide, and other trace gases in the atmosphere. Visible light from the Sun heats the Earth's surface. and one most sensitive to change. Climate experts need to understand the tropical thermostat in order to predict how it will function when global temperatures increase. A major international experiment planned for later this year in the western Pacific should provide some of the needed information. |
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