Milankovitch cycles

Individual violent volcanic eruptions, for example, may affect large-scale climate for one or two years whereas Milankovitch cycles affect climate over... 

Solar Constant solar irrad-iance sunspots Milankovitch cycles... 

Eccentricity variations change the average Earth-sun distance such that annual insolation changes by approximately 0.2%, or 0.5 W/m at the Earth s surface (Crowley and North, 1991). This is small compared to the 10% seasonal changes associated with the other Milankovitch cycles. That a 100 kyr periodicity characterizes both the eccentricity and the glacial-interglacial... 

Milankovitch cycles Changes in global ice volume that reach maxima every 23,000, 41,000, and 100,000 years. They are thought to be related to changes in astronomical alignments that have similar periods. 

Geologists in the nineteenth century deduced that the Earth has experienced several ice ages, during which the ice sheets that cover the poles today reached much farther afield. In 1930 the Serbian mathematician Milutin Milankovitch showed how changes in the shape of the Earth s orbit around the Sun could trigger an ice age by altering the seasonal distribution of sunlight at the planet s surface. There are three cyclic variations in the orbit, with periods of 23,000, 41,000, and 100,000 years. The interplay of these Milankovitch cycles produces a complex but predictable and slow variation in climate over hundreds of thousands of years. 

Demonstration of the complex curves that result from combination of sine waves with amplitudes of 100,41 and 23 ky, the three predominant Milankovitch cycles. Combinations of the three sine curves illustrate the difficulty in backing out cycles from the data. The compilation here does not look like 5 0 vs. depth curves in ocean sediments because the amplitudes are the same in the illustration. Redrawn from Ruddiman (2001). 

The climatic cycles caused by these orbital factors are called Milankovitch cycles after the Serbian mathematician Milutin Milankovitch, who first described them in 1920. Superimposed on the Milankovitch cycles are changes in the Sun that occur over days or months or a few years. 

First, Earth s tilt changes from 22° to 24.5° and back again every 41,000 years. Second, the month when Earth is closest to the Sun also varies over cycles of 19,000 and 24,000 years. Currently, Earth is closest to the Sun in January. This month-of-closest-approach factor can make a difference of 10% in the amount of solar radiation reaching a particular location in a given season. Last, the shape of Earth s orbit varies from being nearly circular to being more elliptical with a period of 1(X),000 years. The climatic cycles caused by these orbital factors are called Milankovitch cycles after the Serbian mathematician Milutin Milankovitch, who first described them in 1920. Superimposed on the Milankovitch cycles are changes in the Sun that occur over days or months or a few years. Over the period 1979 to 1990, for example, total solar irradiance varied by about 0.1 % (Hickey et al., 1988 Willson and Hudson, 1988). 

Milankovitch cycle (see Chapter I), slow changes in the Earth s orbit that modify the seasonal cycle of solar radiation at the Earth s surface. 

Milankovic, Milutin (1879-1958) Serbian civil engineer and geophysicist, best known for his theory of ice ages, relating variations of the earth s orbit and long-term climate change, now known as Milankovitch cycles. 

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