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Abstract

The climate of the Earth, like planetary climates in general, is broadly
controlled by solar irradiation, planetary albedo and emissivity as well
as its rotation rate and distribution of land (with its orography) and
oceans. However, the majority of climate fluctuations that affect
mankind are internal modes of the general circulation of the atmosphere
and the oceans. Some of these modes, such as El Nino-Southern
Oscillation (ENSO), are quasi-regular and have some longer-term
predictive skill; others like the Arctic and Antarctic Oscillation are
chaotic and generally unpredictable beyond a few weeks. Studies using
general circulation models indicate that internal processes dominate the
regional climate and that some like ENSO events have even distinct
global signatures. This is one of the reasons why it is so difficult to
separate internal climate processes from external ones caused, for
example, by changes in greenhouse gases and solar irradiation. However,
the accumulation of the warmest seasons during the latest two decades is
lending strong support to the forcing of the greenhouse gases. As models
are getting more comprehensive, they show a gradually broader range of
internal processes including those on longer time scales, challenging
the interpretation of the causes of past and present climate events
further.