No Escape: Thaw Gains Momentum

By ANDREW C. REVKIN

Correction Appended

In 1969 Roy Koerner, a Canadian government glaciologist, was one of four men (and 36 dogs) who completed the first surface crossing of the Arctic Ocean, from Alaska through the North Pole to Norway.

Now, he said, such a trek would be impossible: there is just not enough ice. In September, the area covered by sea ice reached a record low. "I look on it as a different world," Dr. Koerner said. "I recently reviewed a proposal by one guy to go across by kayak."

At age 73, Dr. Koerner, known as Fritz, still regularly hikes high on the ancient glaciers abutting the warming ocean to extract cores showing past climate trends. And every one, he said, indicates that the Arctic warming under way over the last century is different from that seen in past warm eras.