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SOURCE: The New Yorker

DATE: September 21, 2017

SNIP: Every spring, in alpine regions around the world, one of Earth’s tiniest migrations takes place. The migrants are single-celled green algae; they are kin to seaweed, but instead of living in the sea they live in snow. (Snow weed, maybe?) They spend the winter deep in the snowpack, atop last summer’s snow, as dormant cysts. In the spring, they wake and swim up through the trickle of snowmelt to the surface, dividing and photosynthesizing as they go. Then, at the top, they turn red. This creates what scientists call pink snow or watermelon snow—drifts and glaciers that look like Slush Puppies and eventually reduce to rivulets of crimson.

Watermelon snow is a perfectly natural phenomenon, but in an age of disappearing glaciers it is also problematic. Last year, scientists discovered that the algae had reduced the amount of sunlight reflected by some glaciers in Scandinavia—and increased the amount of sunlight absorbed—by thirteen per cent. The result, as Dial and his colleagues demonstrated in this month’s issue of Nature Geoscience, is faster melting. As in other parts of the warming planet—particularly the Arctic, where scientists fear that thawing permafrost may be triggering a climatic feedback loop—the effect is likely self-perpetuating. Ice sheets are already being darkened by dust, soot, and ash, which hasten melting and add nutrients on which algae can flourish. As the organisms proliferate, they melt even more snow, which allows them to proliferate again. “It spreads more rapidly than people realize, once it gets established,” Dial said.