climatic change

(climatology) The long-term fluctuation in rainfall, temperature, and other aspects of the earth's climate.

Evidence of climatic change ranges from differing geological strata to the study of pollen grains and tree rings.

The early climatic history of the world is not well understood but it is known that during the last 55 million years the earth has been cooling, and that during the last million years there has been alternating of glacial and interglacial episodes. see little ice age.

External causes of climatic change may include: changes in solar output; changes in the number of sunspots which seems to vary in an 11-year cycle, changes in the ellipticity of the earth's orbit, which roughly follows a 100 000-year cycle, and changes in the earth's axis of rotation, which alters the season of perihelion, and which follow an approximately 100 000-year cycle. see milankovitch cycles.

Internal causes include vulcanicity, which can increase the density of atmospheric nuclei in the atmosphere, variations between the distribution of land and sea, continental drift, and changes in the atmosphere-surface-ocean system.

In 1995 the Inter-Government Panel on Climatic Change reported that ‘the balance of evidence suggests that there is a discernble human influence on the global climate’, to which the 1997 Kyoto Protocol was a response. (G. O'Hare, Area 32.) See also carbon management, carbon tax, greenhouse effect.