Source: AP|Published: Thursday March 15, 9:42 AM
http://www.theage.com.au/breaking/0103/15/A29509-2001Mar15.shtml
LONDON - Scientists say a British comparison of satellite data from 1970
and 1997 has yielded the first direct evidence that so-called greenhouse
gases are building up in Earth's atmosphere and allowing less heat to
escape into space.
The study, reported in the journal Nature, contains no evidence on whether
Earth's surface temperature is actually increasing.
In fact, whether this greenhouse effect will lead to global warming or
global cooling is unclear, the scientists said.
That is because the greenhouse effect could start a cycle in which more
clouds are formed, stopping the sun's energy from reaching Earth's surface
in the first place, said London scientist John Harries, who led the study.
Scientists have long theorised that carbon dioxide and other waste gases
are increasing the trapping of heat close to Earth in what is called a
greenhouse effect.
Harries and his colleagues at London's Imperial College compared readings
of infrared light from the Earth's surface and found less was escaping
into space in 1997, specifically in the wavelengths known to be absorbed
by greenhouse gases such as carbon dioxide, methane and ozone.
"We're absolutely sure, there's no ambiguity. This shows the greenhouse
effect is operating and what we are seeing can only be due to the increase
in the gases," Harries said.
Evidence was also found of smaller increases in chlorofluorocarbons,
refrigerants blamed for destroying the ozone layer that protects Earth
from ultraviolet radiation.
Atmospheric scientists not involved in the study said the satellite data
provided concrete confirmation that greenhouse gases were building up.
The findings come as political debate intensifies over whether global
warming is a real danger.
A report released in January in China by an international panel predicted
global temperatures could rise as much as 5.8 degrees Celsius (10.5
degrees Fahrenheit) over the next century, primarily because of pollution.
American and European environmental officials, however, have not been able
to agree on how to implement the 1997 Kyoto Protocol, which calls for
reductions in greenhouse-gas emissions.
Yesterday, President George W. Bush backed away from a campaign pledge to
regulate carbon dioxide from coal-burning power plants, saying mandatory
controls would lead to higher electricity prices.
In the British study, the researchers compared data from the Japanese
ADEOS satellite, which produced about nine months of data starting in
1996, and NASA's Nimbus 4 satellite between April 1970 and January 1971.
Only clear-sky readings of the atmosphere over the central Pacific were
compared.
Drew Shindell, an atmospheric physicist at NASA's Goddard Institute for
Space Studies in New York, said the research should end the debate over
the greenhouse effect, but not over how to address the problem.
"One of the main things that cause people to be skeptical of global
warming is the lack of that real, definite connection between greenhouse
gases and the planet getting warmer," Shindell said. "This really gives
concrete evidence for the first time that greenhouse gases are changing
the energy balance of the planet."
While the greenhouse effect supposedly causes warming, that in turn
increases water vapor in the atmosphere, which affects the formation of
clouds, which can reflect the sun's energy back into space. The net effect
could be cooling, but more research was needed, Harries said.
"The effect of clouds on the planet is very complex, and frankly we don't
understand it," Harries said.
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