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Milankovich, Milutin

ice earth’s co2 changes

(1879–1958) Serbian climatologist: developed astronomical theory of climatic change.

Milankovich was educated in Vienna, but in 1904 moved to the University of Belgrade, where he spent the rest of his academic career. He is remembered for his work on the cause for long-term changes in the Earth’s climate. Following earlier proposals by and J Croll (1821–90), he recognized that the major influence on the Earth’s climate is the amount of heat received from the Sun. Three astronomical factors can affect this: the eccentricity of the Earth’s orbit (which varies on a time scale of about 100 000 years), the tilt of the Earth’s axis (time scale of 40 000 years), and a precessional change which determines whether the northern or southern hemisphere receives most radiation (time scale of 20 000 years). Milankovich spent 30 years computing the amount of radiation received at different latitudes for the past 650 000 years, and was able to demonstrate that changes in insolation corresponded with the then known ice ages. Since Milankovich’s work in the 1920s, the number of known ice ages has increased, and their history is seen as complex. Although the Earth’s orbital variations are important, it is now clear that as well as the cooler summers studied by Milankovich and ascribed by him to these orbital variations, other factors probably contributed to ice age formation. One such is the level of CO2 in the atmosphere; both studied the way in which loss of CO2 and therefore of its ‘greenhouse effect’ could cool the Earth, and interest in this rose in the 1970s after study of air bubbles trapped in polar ice cores gave information on CO2 levels over a long period. Certainly over the last million years the oceans have varied in temperature and volume, with the global ice mass changing by some 10 19 kg and resulting in changes in sea level of up to 100 m. Over the same period, CO2 has varied by up to 30%. A complete theory of factors leading to ice ages must be complex, and good models are not yet available.

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