Pollutants contribute to Arctic warming some more

The Arctic climate is already sensitive to global warming; now it turns out human pollutants are kicking it — or rather, warming it more — while it’s down. According to a new study in Nature, particulate pollution (mostly from cities in Europe) changes the size and number of water droplets in clouds above the Arctic, increasing their ability to trap heat. On particularly hazy days, especially in the winter when there’s little precipitation to wash out pollutants, the effect causes the Arctic surface to grow 2 to 3 degrees warmer than it would be under clean air. Particulate pollution is known to help clouds reflect sunlight and thus reduce surface temperature — so-called “dimming” — so the discovery that it contributes to warming is an unfortunate surprise. The Arctic really can’t catch a break.