The greenhouse effect and climate change revisited

On any planet with an atmosphere, the surface is warmed not only by the Sun directly but also by downward-propagating infrared radiation emitted by the atmosphere. On the Earth, this phenomenon, known as the greenhouse effect, keeps the mean surface temperature some 33 K warmer than it would otherwise be and is therefore essential to life.The radiative processes which are responsible for the greenhouse effect involve mainly minor atmospheric constituents, the amounts of which can change either naturally or as a by-product of human activities. The growth due to the latter is definitely tending to force a general global surface warming, although because of problems in modelling complicated feedback processes, for example those involving water vapour, ozone, clouds and the oceans, the precise rates of change and the local patterns which should be expected are not simple to predict. This article updates an earlier review which discussed the physical processes involved in the greenhouse effect and theoretical and experimental work directed towards an understanding of the effect on the climate of recent and expected changes in atmospheric composition. In the last ten years, progress in data acquisition and analysis, and in numerical climate modelling, has tended to confirm earlier predictions of the likelihood of significant rises in the mean surface temperature of the planet in the next 50-100 years, although this remains controversial. (author)