Study May Prove Greenhouse Effect

March 14, 2001 / 1:56 PM EST / CBS/AP

A comparison of satellite data from 1970 and 1997 has yielded what scientists say is 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 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 John Harries, who led the study.

Scientists have long theorized 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.

The study was reported in Thursday's issue of the journal Nature.

Atmospheric scientists not involved in the study said the satellite data provide concrete confirmation that greenhouse gases are building up.

The findings come as the 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 10.5 degrees Fahrenheit over the next century, primarily because of pollution.

The Protocol

The Kyoto Protocol was signed in Kyoto, Japan, on Dec. 11, 1997. It goes into effect once 55 countries have ratified it. So far 84 countries, including the United States, have signed the protocol, but only 32, of which the U.S. is not one, have ratified it.

The agreement requires the U.S. to cut greenhouse gas emissios at 7 percent below 1990 levels between 2008-2012.

Read the text of the Protocol.

See a list of countries that've signed and/or ratified the treaty.

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.

On Tuesday, 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 is needed, Harries said.

"The effect of clouds on the planet is very complex, and frankly we don't understand it," Harries said.

Scientists will have more opportunities to compare infrared data following the launch by NASA later this year of a new satellite carrying the first of the next generation of infrared instruments.

By ALEX DOMINGUEZ