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 the Earth's atmosphere and preventing the escape of some excess heat into space.
The study contains no evidence on whether the Earth's surface temperature is increasing. 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 the Earth's surface, 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 the Earth in what is called a greenhouse effect.