Letters to Nature

Nature 410, 355-357 (15 March 2001) | doi:10.1038/35066553; Received 17 May 2000; Accepted 15 January 2001

Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997

John E. Harries, Helen E. Brindley, Pretty J. Sagoo & Richard J. Bantges

  1. Space and Atmospheric Physics Group, Blackett Laboratory, Imperial College, London SW7 2BW, UK

Correspondence to: John E. Harries Correspondence and requests for materials should be addressed to J.E.H. (e-mail: Email: j.harries@ic.ac.uk).

The evolution of the Earth's climate has been extensively studied1, 2, and a strong link between increases in surface temperatures and greenhouse gases has been established3, 4. But this relationship is complicated by several feedback processes—most importantly the hydrological cycle—that are not well understood5, 6, 7. Changes in the Earth's greenhouse effect can be detected from variations in the spectrum of outgoing longwave radiation8, 9, 10, which is a measure of how the Earth cools to space and carries the imprint of the gases that are responsible for the greenhouse effect11, 12, 13. Here we analyse the difference between the spectra of the outgoing longwave radiation of the Earth as measured by orbiting spacecraft in 1970 and 1997. We find differences in the spectra that point to long-term changes in atmospheric CH4, CO2 and O3 as well as CFC-11 and CFC-12. Our results provide direct experimental evidence for a significant increase in the Earth's greenhouse effect that is consistent with concerns over radiative forcing of climate.