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

The evolution of the Earth's climate has been extensively studied(1,2), and a strong link between increases in surface temperatures and greenhouse gas es has been established(3,4). But this relationship is complicated by sever al feedback processes-most importantly the hydrological cycle-that are not well understood(5-7). Changes in the Earth's greenhouse effect can be detec ted from variations in the spectrum of outgoing longwave radiation(8-10), w hich is a measure of how the Earth cools to space and carries the imprint o f the gases that are responsible for the greenhouse effect(11-13). Here we analyse the difference between the spectra of the outgoing longwave radiati on of the Earth as measured by orbiting spacecraft in 1970 and 1997. We rnd differences in the spectra that point to long-term changes in atmospheric CH4, CO2 and O-3 as well as CFC-11 and CFC-12. Our results provide direct e xperimental evidence for a significant increase in the Earth's greenhouse e ffect that is consistent with concerns over radiative forcing of climate.