Abstract
Earth’s greenhouse effect is manifested as the difference between
thermal infrared radiation emitted at the Earth surface and that emitted
to space at the top of the atmosphere. This difference is due mainly to
absorption and downward emission of radiant energy by atmospheric trace
gases. The greenhouse effect is an essential feature of Earth’s climate
system that results in global mean surface temperature about 32 K
greater what it would otherwise be for the same planetary absorption of
solar radiation. Increases in atmospheric carbon dioxide, methane,
nitrous oxide, and chlorofluorocarbons due to human activities over the
past 200 years have increased the greenhouse effect by about 1%
relative to the radiative fluxes that drive the climate system. The
resultant increase in global temperature and other changes in climate
are of great societal concern. This article introduces the physics of
the greenhouse effect and more broadly of Earth’s climate system and of
climate change and provides resources for further study. It reviews the
processes responsible for the greenhouse effect, the anthropogenic
increase in the greenhouse effect, and the response of the climate
system to this increase. Developing prognostic capability to determine
this response to an accuracy that would be useful to inform policymaking
is the major challenge facing climate scientists today.