Comparisons of data obtained from satellites that orbited Earth more than 25 years apart provide rare, direct evidence that the planet's greenhouse effect increased significantly during the closing decades of the 20th century. These new findings support abundant indirect indications that greenhouse gases, such as carbon dioxide and methane, are warming Earth's atmosphere.
Spectrometers showed that more of the infrared radiation emitted by Earth and leaving the atmosphere was blocked by heat-absorbing greenhouse gases in 1997 than in 1970. This indicates that the planet's natural cooling mechanism has lost some of its effect, says Helen E. Brindley, an atmospheric physicist at Imperial College in London. She and her colleagues report their findings in the March 15 Nature.
The British researchers used two sets of satellite data: One was collected in 1970 by instruments flown on NASA's Nimbus 4, and the other was obtained in 1997 from Japan's Advanced Earth Observ