How it began
Milutin Milankovitch was born in 1879 in Dalj, then in Austria-Hungary and now in Croatia. In 1909 he took up a professorship in applied mathematics at the University of Belgrade, where he stayed until retirement 46 years later. In 1911 he began calculating by hand how much solar radiation reached different latitudes over the past 600,000 years, work that occupied him for thirty years. He published a mathematical theory of solar heating in 1920, a treatise on mathematical climatology in 1930 and, in 1941, the Canon of Insolation and the Ice-Age Problem.
How it works
Milankovitch examined three orbital movements. Eccentricity is the changing shape of the orbit, with a cycle of roughly 96,000 to 100,000 years. Obliquity is the tilt of the axis, which shifts between about 21.5 and 24.5 degrees over about 41,000 years. Precession is the wobble of the axis, with a period of about 23,000 years. Together they change the sunlight reaching mid and high northern latitudes by 20 percent or more. He held that summer sunshine in the far north controls whether ice sheets grow or retreat.
Who pushed back
His work was at first greeted with excitement but was largely dismissed because ice ages were hard to date. During the 1950s it was challenged and fell out of favor. Scientists thought the temperature changes he predicted were too small to matter, and some deposits that had been taken as glacial turned out to be something else. Milankovitch died in 1958 with the theory still in doubt.
What lasted
By the late 1960s deep-sea sediment cores revealed regular variations that matched his figures. In 1976 a study in the journal Science by Hays and colleagues found that the cycles correspond with periods of major climate change over the past 450,000 years. Milankovitch had calculated ice ages about every 41,000 years. Later research confirmed that interval for the period between one and three million years ago, though the rhythm lengthened to 100,000 years about 800,000 years ago.
Where it stands today
NASA describes the theory that these cycles drive the timing of glacial and interglacial periods as well accepted. Open questions remain, including the relative roles of precession and obliquity and the reason the ice age rhythm shifted to 100,000 years. The cycles now carry his name.
