Milutin Milankovitch

Milutin Milankovitch (born May 28, 1879, Dalj, Austria-Hungary [now in Croatia]—died December 12, 1958, Belgrade, Yugoslavia [now in Serbia]) was a Serbian mathematician and geophysicist, best known for his work that linked long-term changes in climate to astronomical factors affecting the amount of solar energy received at Earth’s surface. His ideas were published in a series of papers and eventually brought together in his influential book Kanon der Erdbestrahlung und seine Anwendung auf das Eiszeitenproblem (1941; Canon of Insolation and the Ice-Age Problem).

Early life

Milankovitch was born into a large well-to-do Serbian family. After local schooling, he traveled to Vienna at age 17 to study engineering at the Technische Hochschule (College of Technology). After graduation and a short hiatus for military service, he returned to Vienna and earned a doctorate in 1904 for theoretical research on concrete and the design of concrete structures. That led to a successful but short career as an engineer working on complex projects throughout the Austro-Hungarian Empire. During that period he devised and patented new approaches to concrete construction.

In 1909 Milankovitch left Vienna and took up a professorship in applied mathematics at the University of Belgrade, where he remained until retirement 46 years later. He was a popular teacher, but his true passion was research. He sought to apply his mathematical skills to areas that had not yet been extensively studied. Milankovitch wanted, he said, to find an “arable field” that he could “cultivate with my mathematical tools,” and he found it in meteorology, which was at the time predominantly an empirical science—that is, a science that relied on observation.

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Milankovitch cycles

Milankovitch’s goal was to calculate the temperature at different points on the surface of Earth at different times of year from axioms, or first principles. That was a formidable problem. However, his initial calculations, published in Théorie mathématique des phénomènes thermiques produits par la radiation solaire (1920; “Mathematical Theory of Thermal Phenomena Caused by Solar Radiation”), gave results that were roughly in line with empirical data concerning early 20th-century temperatures, and they thus immediately attracted the attention of meteorologists. In 1924, in collaboration with German meteorologist Vladimir Köppen and German geophysicist Alfred Wegener, who were then working on the causes of ice ages, Milankovitch extended his longhand calculations hundreds of thousands of years into the past to assess the effect of known regular changes in three astronomical parameters: the obliquity (tilt) of Earth’s axis of rotation, the precession (wobblelike movement) of the rotation axis, and the eccentricity (a measure of the elliptical shape) of Earth’s orbit around the Sun. Those three parameters govern the amount of solar radiation (insolation) that strikes Earth’s surface at different latitudes in different seasons. Because they operate on different timescales, the parameters affect climate by interacting in a manner that sometimes increases and sometimes decreases the insolation at a particular location.

Milankovitch worked tirelessly to construct the radiation curves at latitudes 55°, 60°, and 65° N—which were deemed most important for affecting the advance and retreat of large-scale ice caps in the Northern Hemisphere—that appeared in Die Klimate der geologischen Vorzeit (1924; “Climate of the Geological Past”) by Wegener and Köppen. Curves for selected lower latitudes were presented in Milankovitch’s Mathematische Klimalehre und astronomische Theorie der Klimaschwankungen (1930; “Mathematical Climatology and the Astronomical Theory of Climatic Changes”). Both sets of calculations were contained within his masterwork, the Kanon of 1941.

Milankovitch’s work was challenged during the 1950s, and it soon fell out of favour. Most scientists thought that Milankovitch’s predicted temperature changes were too minor to choreograph the advance and retreat of glaciers. Perhaps more important, several European glacial deposits with ages that coincided with Milankovitch’s predicted cool periods turned out not to be glacial deposits at all, and that development cast doubt on the principal evidence used to support his theory.

His work was vindicated in the 1970s, however. High-resolution studies of deep-sea cores confirmed that glacial periods, as reflected in seawater temperatures, precisely follow Milankovitch’s predictions over roughly the past one million years. Those studies provided evidence for cyclical climate change in the past with periods of approximately 100,000, 41,000, and 23,000 years, coinciding with the astronomical cycles in eccentricity, axial tilt, and precession, respectively. The astronomically timed variations in solar radiation are now known as Milankovitch cycles.

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Other interests

Milankovitch was interested in making science accessible to nonscientists. For several years in the 1920s he wrote a monthly “letter” in a Serbian magazine to a young imaginary friend, in which he described mental journeys into the past to visit famous scientists and explore their ideas, especially as they related to astronomy. The letters were later collected and published as the book Kroz vasionu i vekove: pisma jednog astronoma (1928; “Through Distant Worlds and Times: Letters from a Wayfarer in the Universe”).