Tropics leave trace in Arctic warming

Cooling temperatures in the waters of the tropical Pacific Ocean may be responsible for some of the recent rapid warming of the atmosphere above northeastern Canada and Greenland. The finding, reported May 8 in Nature, suggests that half of the warming in the Arctic region is a result of natural forces, while the other half comes directly from the effects of human activities. The extent of human effects on Pacific temperatures is not yet clear, the scientists note.