Milankovitch Milutin 18791958

MILUTIN MILANKOVITCH, BORN in Dalj, Serbia on May 28, 1879, graduated from the Institute of Technology in Vienna, Austria in 1904. He worked as an engineer in Vienna before returning to Serbia, in 1905, to teach applied mathematics at the University of Belgrade. During the first Balkan War in 1912, he served in the military, assigned to the Danube division of the Serbian army. Milankovitch had begun a project to calculate temperatures at different latitudes and how temperature changed as a result of astronomical rhythms.

His goal was to explain the role played by astronomical cycles on ice ages by determining where various astronomical cycles coincided and combined to influence the amount of solar radiation leading to climate change.

After World War I, Serbia joined with other Balkan countries to become part of Yugoslavia. The political environment of the Balkan area remained in flux, including involvement in the Balkan War, World War I, and World War II. In spite of the unrest in the region, and an arrest and imprisonment as a prisoner of war, Milutin Milankovitch continued his work to determine, mathematically, the cycles of ice ages. He built on the theory that the ice ages were cyclical, and the work on astronomical rhythms by Scottish geologist James Croll.

Milankovitch completed a series of astronomical calculations using only his brain as the calculator, a writing implement, and paper. His calculations took into account the factors of the Earth's orbit, including tilt, axis of rotation, and axis of spin to determine the amount of insolation (sunlight, or the amount of solar radiation received by the Earth). He calculated detailed insolation curves for a few different northern latitudes, ranging back 650,000 years, and then calculated how ice sheets would respond to temperature changes. In addition, he performed similar insolation curve calculations for Mars and Venus.

His climate calculations took into account the distance from the Sun, the latitude and angle at which the Sun struck the surface of the planet. He focused on obliquity (the amount of axial tilt) and the precession of the equinoxes. He concluded the effect of eccentricity (the elliptical path of the orbit around the Sun) would be small, though later scientists have shown the importance of eccentricity. He postulated that insolation in the Northern Hemisphere drove the climate system because two-thirds of Earth's land mass lies in the Northern Hemisphere. He believed summer insolation levels at a boundary of 65 degrees N latitude, just south of the Arctic Circle, played a crucial role. If the ice caps survived the higher temperatures of summer below that specific latitude, the ice caps would have an increased chance of advancing, and by extrapolation, if the ice caps grew, the climate would cool.

His theory and calculations caused excitement among his contemporaries, but with no means of cor-roboration, his theory was shelved. Milutin Milanko-vitch died on December 12, 1958, before his research and theories had returned to prominence in the field. Since his death, in addition to using computers for improved accuracy, scientists have used carbon dating and the advanced ability to take remove cores from the ocean floor for comparison. Milankovitch's work returned to prominence. Despite flaws, and the fact that astronomical factors are not the only causes of climate change, scientists have shown a significant correlation between the climate record and Milankovitch's cyclical calculations. His work was established as a scientific model called the Milankovitch cycles in the 1970s.

SEE ALSO: Croll, James; Ice Ages; Milankovitch Cycles.

BIBLIOGRAPHY. Mark Bowen, Thin Ice Unlocking the Secrets of Climate in the World's Highest Mountains (Henry Holt and Co., 2005); John Gribbin, The Scientists: A History of Science Told Through the Lives of its Greatest Inventors (Random House, 2002); National Geophysical Data Center, "Milutin Milankovitch's Major Cycles," www.ngdc.noaa. gov (cited July 2003).

LYN MlCHAUD Independent Scholar

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