“Return to previous Arctic conditions is unlikely,” according to an international group of scientists from countries including Canada, the U.S., Russia and Denmark, Reuters reports. Conditions there have a powerful impact on weather in middle latitudes of the Northern Hemisphere, where much of the population lives, and last winter’s heavy snows in the U.S., northern Europe and western Asia are linked to higher air temperatures in the Arctic, they found. There is widespread evidence of Arctic warming, they agreed, with surface air temperatures rising above global averages twice as quickly as the rate at lower latitudes, partly because of a process called polar amplification. This is when warming air melts snow and ice, which is white, to show darker water or land, which absorbs heat and speeds the effects of global warming. In the round-the-clock sunlight of Arctic summers, it happens even faster.