Now It's Serious: As the World Warms, Lemmings Take a Hit

Sure, effects of global warming such as more-intense hurricanes and exacerbated drought/flood cycles are no picnic, but now things are getting really dire: as the world, especially the top of the world, warms, the periodic explosion and crash of lemming populations is history.

It's been a decade since the last massive population explosion that lemmings in southern Norway have experienced for at least the last 1,000 years—typically once every three to five years: the explosion and crash of lemming populations has not been observed since the late 1990s, scientists at the University of Oslo led by Nils Stenseth are reporting in the journal Nature today. It's yet another canary-in-the-coal mine for climate change.

What seems to be happening, they say, is that lemmings and other small rodents depend on the insulated region beneath the snow to stay warm, find food (mostly moss) and stay out of sight of predators such as foxes, owls and birds of prey. Without all of the above, their young (of which females often produce 12 per litter, and three litters per year) do not survive. But recent increases in temperature and humidity are, basically, producing the wrong kind of snow.

Lemmings need a space between the ground and the snow. Such a space forms when warmth from the ground melts a thin layer of snow above it, leaving a gap called a “subnivean space” above the ground (which absorbs the snowmelt). But with rising temperatures, the gap is less likely to form: repeated episodes of warmth cause the snow to melt and refreeze over and over, producing a sheet of ice over the ground (rather than just an air-filled space) that keeps lemmings from feeding on the moss. Fewer offspring survive. As a result, populations do not soar and neither do they crash (as a result of too many mouths to feed).

What is going to happen to the simile, “behaving like lemmings”?