He was a geography professor at the University of Colorado at Boulder, where he headed the Cooperative Institute for Research in Environmental Sciences (CIRES).
He received the equivalent of a bachelor's degree and a doctorate from the Swiss Federal Institute of Technology in Zurich (known as ETH Zurich). He was eventually a member of its faculty.
He was a prominent glaciologist whose 30-year study of Greenland's ice sheet confirmed global warming. He also conducted research in Antarctica.