Milutin Milankovitch  was a Serbian astrophysicist 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. These ideas were derived from improved methods of calculating variations in Earth's eccentricity, precession, and tilt through time and determining their combined effects on long-term climate change. Although Milankovitch cycles do appear to explain some aspects of long-term climate change, shorter-term changes, like the current global warming trend on Earth, are not due to Milankovitch cycles. Scientists now attribute some of that change in climate to human release of greenhouse gasses.

After graduating from high school and spending an obligatory year in military service, Milutin borrowed money from an uncle to pay for additional schooling at the Technical High School in engineering. He researched concrete and wrote a theoretical evaluation of it as a building material. At age twenty-five, he proudly became the first Serbian Doctor of Technical Sciences. He then worked for an engineering firm in Vienna, using his knowledge to design structures. He obtained several patents relating to methods of building with reinforced concrete.

But being a full time engineer was not to be Milutin’s profession. Working on his dissertation convinced him that he loved scientific research and he saw that as his life’s passion. On his own, he further developed his abilities in mathematics, physics and astronomy. In 1909, Milutin left Vienna because political events made it difficult for Serbs to live in Austria. Fortunately, he was offered a ‘Chair of Applied Mathematics’ at the University of Belgrade in Serbia. There he taught rational mechanics, celestial mechanics, and theoretical physics and began scientific research. Within a year he changed his citizenship from Austro-Hungarian to Serbian.

Milutin’s research plan was to find a challenging problem in science and spend the rest of his life solving it. It also needed to use his mathematical abilities. He had limited library resources and was far removed from the scientific centers of Europe, so he knew that competing on cutting edge topics would be difficult. For this reason, Milutin sought a problem that others were not pursuing. He began to investigate meteorology, but most of the research at the time involved data analysis and not the interplay between math and physics that he found most rewarding. Two papers, however, sparked his interest. They were theoretical papers on the receipt of solar energy over Earth’s surface. He found fatal flaws in both papers and decided to pursue the subject on his own. His early research on meteorology also introduced him to the topic of ice ages and he saw an opportunity to explain the climatic variations involved in the advances and retreats of the ice sheets. 

He outlined a two part ‘cosmic problem’ to solve, with an astronomical and a physical component. The orbits of the planets around the Sun are highly predictable and vary over time. Each planet’s axis of rotation also varies over time in both the angle of the tilt and the direction the axis points. Each cycle works on a different time scale and each affects the amount of solar energy received by the planets. Others had suggested that these cycles may have caused the ice ages, but Milankovitch sought to investigate the issue with enough detail to solve the problem.

The physical part of his cosmic problem was to describe how the Sun’s rays determine the temperature on Earth’s surface after passing through the atmosphere. His goal here was to develop a mathematical theory describing Earth’s climate zones. If he could achieve this for the present climates, he could use his astronomical findings to determine climates of the past and future. He began publishing papers on various aspects of his research in 1912.

In 1914, when he was thirty five years old, Milutin married Christine Topuzović, the thirty year old daughter of an old merchant family who had studied to be an opera singer.  After they married, though, she only sang for family and friends. Two weeks after they wed, a Serb assassinated Prince Ferdinand of Austria and the Austro-Hungarian Empire declared war on Serbia. Milutin became a prisoner of war and was sent to a camp in Hungary. Christine traveled to Vienna and asked Milutin’s former mathematics professor to intervene on his behalf. After six months in the camp, he was allowed to live in Budapest if he reported to the police every week, agreed that his correspondence would be examined, and obtained permission for any travel. There, Christine and he lived for the duration of the First World War and their son Vasko, their only child, was born in 1915. During this time Milutin pursued his scientific interests with the help of the Hungarian Academy of Sciences.

After five years, the family returned to Belgrade, which became the capital of the newly created Yugoslavia. From his research in Budapest, Milutin wrote a book and soon found an opportunity to have it published. He wrote it in German but had to translate it into French for publication. Mathematical Theory of Heat Phenomena Produced by Solar Radiation appeared in 1920 and presented his theories on both the astronomical and physical parts of his cosmic problem. In the book he calculated, using physical principles, the average yearly temperature at various latitudes on Earth and his values were reasonably close to the empirical temperature record. Satisfied that he could calculate present temperature patterns, he predicted climates over the last 130,000 years, accounting for changes in the shape of Earth’s orbit, the tilt of the axis of rotation and timing during the year of the equinoxes. He also calculated the temperatures of the other planets and the Moon.

For a short time after his book was completed, Milankovitch worked on stellar astronomy, checking Einstein’s assertion that the speed of light is constant regardless of the speed of the light source. But in 1922, he received a letter from the German climatologist Wladimir Köppen. Köppen and his son-in-law Alfred Wegener were working on climates of the past and asked Milankovitch if he would join them in the endeavor. He had already calculated past climates for 130,000 years and Köppen felt that his results matched the geomorphological evidence of glaciations in Europe. But the glaciations extended back at least 600,000 years, so Milankovitch was asked to extend his work further back in time. They agreed that he would calculate solar radiation changes at the top of the atmosphere at 55°, 60° and 65° North Latitude. Summer temperatures, they felt, were particularly important with respect to the onset of glaciations, due to the melting of winter snowfall. After he determined the correct procedure to follow, he spent 100 days doing the calculations and prepared a graph of the variations in the receipt of solar radiation. Geomorphologists then used the graph to see if it agreed or disagreed with the field evidence of glaciations.

Milankovitch first met Wegener in 1924 while attending a conference in Innsbruck, Austria and the two spent a late night at a beer garden discussing their work. Wegener gave an outline of his theories of continental drift and past climates the next day. His discussion of climatic changes during the Quaternary drew heavily on Milankovitch’s work. The next year, Milutin and his family vacationed in a small town in Austria near Graz, where Wegener and Köppen lived. The three became close friends, both personally and professionally.

Köppen asked Milankovitch to write the introductory portion of a multivolume Handbook of Climatology in 1927. Köppen felt that Milankovitch’s theoretical approach to solar energy was the logical topic to begin the series. Milutin used this as an opportunity to expand his theory of the effects of the atmosphere on solar energy. He also considerably improved and expanded his work on the three astronomical cycles and their effects on climate. When he finished his section, the publisher decided that it was important enough to warrant its own book and published it in 1930, in German, as Mathematical Climatology and Astronomical Theory of Climate Change.

Conversations with Wegener got Milankovitch interested in the interior of the Earth and the movement of the Poles and he told his friend that he would investigate polar wandering. Unfortunately, Wegener died in 1930 during a research expedition to Greenland, but Milutin carried out his promise. He became convinced that the continents ‘float’ on a somewhat fluid subsurface and that the positions of the continents with respect to the axis of rotation affect the centrifugal force of the rotation and can throw the axis off balance and force it to move. He drew a map of the path of the North Pole over the past 300 million years, but carefully pointed out all of the simplifying assumptions he had to make in order to make his predictions. Unlike his climate studies, Milankovitch’s polar wandering work is not particularly influential in modern geophysical research.

In the late 1930s, Milankovitch revised his theories and presented them in his most lasting work, Canon of Insolation and the Ice Age Problem. Its six parts dealt with the orbits of the planets and their mutual perturbations, Earth’s rotation, the movements of the poles, changes in the receipt of solar radiation, the relationships between solar radiation and the atmosphere, and the Ice Ages. As the book was being printed in Belgrade, Germany declared war on Yugoslavia and the city was bombed, including the printing plant. Fortunately for science, only the last thirty two pages were destroyed. They were reprinted once paper could be obtained and the book was bound and published in 1941. 

Milutin suffered a stroke in 1957 and he died the next year. He is buried in his family cemetery in Dalj. Christine died a few years later.

Sources

• Lee, Jeff (Lead Author); Cutler J. Cleveland (Contributing Author); Peter Saundry (Topic Editor). 2009. "Milankovitch, Milutin." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth September 15, 2006; Last revised March 11, 2009; Retrieved May 20, 2009]. 
• Wikipedia Contributors, Milutin Milanković, Wikipedia The Free Encyclopedia, Accessed 20 May 2009.