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 today'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.
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