Willi Dansgaard, a Danish paleoclimatologist who was the first to recognize that the Earth's climatic history was stored in the Greenland ice cap, died Jan. 8 in Copenhagen, according to the Niels Bohr Institute at the University of Copenhagen. He was 88.
His research, together with that of Claude Lorius of France and Hans Oeschger of Switzerland, revolutionized scientific knowledge of how the temperature and composition of the atmosphere have changed over the last 150,000 years, demonstrating a clear link between carbon dioxide and methane concentrations and global temperatures.
Their discoveries launched a major global research effort to understand the mechanisms by which these atmospheric changes are linked to changes in the land surface and particularly to changes in ocean circulation and chemistry.
Dansgaard and his colleagues were not themselves environmental activists or proponents of any particular position on global warming, but their research has provided a strong scientific underpinning for efforts to understand how humanity's continued release of greenhouse gases may affect the planet's future.
Dansgaard's particular discipline was mass spectroscopy, which involves identifying the precise mass of individual molecules. His epiphany in the early 1950s involved the two naturally occurring isotopes of the element oxygen: oxygen-16, which accounts for 99.8% of all oxygen in the environment, and the much rarer, slightly heavier isotope, oxygen-18.
He reasoned that, at colder temperatures, slightly more water molecules containing oxygen-18 would condense as rainfall. To test his theory, he placed beer bottles with funnels in his backyard to collect rainfall at various temperatures and analyzed them to validate his idea. He then obtained rain samples from around the world from the International Atomic Energy Agency — which was tracking fallout from nuclear tests — and confirmed his theory.
Dansgaard later said modestly that that was his only good idea.
He published his results in the journal Tellus in 1964.
American scientists at a Cold War camp in Greenland called Camp Century, 100 miles from the Thule Air Base, had been drilling a core into the ice there for a variety of purposes, military and otherwise. Because of summer melting and refreezing that formed a thin layer of ice on the surface, the ice sheet contained distinctive layers that corresponded to individual years in history going back thousands of years.
The Americans didn't really know what to do with the core, and they gave Dansgaard access to it — although for security reasons he was never allowed to view the actual drilling. Working with Chester C. Langway Jr. from the U.S. Army Cold Regions Research and Engineering Laboratory, he demonstrated that past climate could, in fact, be deduced from analysis of oxygen isotopes in ice cores.
Intriguingly, he observed that, about 15,000 years ago, Greenland abruptly warmed by 16 degrees over a period of 50 years, a great surprise to researchers who had previously assumed that such major changes in climate had to occur over thousands of years. The finding was subsequently confirmed by Oeschger, and such abrupt climate changes are now known as Dansgaard-Oeschger events.
With these successful results, Dansgaard obtained access to the Dye-3 radar station on the ice cap in South Greenland, where the first purely scientifically motivated deep ice core drilling project was carried out beginning in 1979 by a Danish-American consortium. Those results established ice core science as a cornerstone in the study of climate of the past.
Dansgaard later organized or participated in more than 19 expeditions to the glaciers of Norway, Greenland and Antarctica.
Willi Dansgaard was born in Copenhagen on Aug. 30, 1922, and received his education at the University of Copenhagen, including a doctorate in physics. He spent his entire career there as well.
In 1996, he, Lorius and Oeschger shared the Tyler Prize, the highest award in environmental science.
Dansgaard is survived by three children, six grandchildren and one great-grandchild.