By RICHARD A. KERR - SCIENCE - AAAS
Added: Sat, 04 Feb 2012 17:35:39 UTC
For years scientists have debated what could have plunged Europe into the half-millennium-long cold spell that ended only a century ago. Was it the temporarily spotless and therefore faint sun, or did a burst of volcanic eruptions loft debris that shaded out a normal sun? Or were the sun and volcanoes in cahoots? Researchers analyzing plants killed in the Little Ice Age's opening years are now pinning the blame on volcanoes alone.
Solving this climatic whodunit has been hampered by the uncertain timing of the Little Ice Age's onset. So geologist Gifford Miller of the University of Colorado, Boulder, and his colleagues went to the best climate record they could find: intact plants emerging from beneath the retreating ice cap on Canada's Baffin Island. Carbon dating showed that most of the plants died between 1275 and 1300 as Arctic ice suddenly expanded across once-green terrain. The same signal of sudden cooling turned up in sediment from the late 1200s deposited in a glacier-fed lake in Iceland.
Both high-latitude cooling signals coincide with an exceptional burst of activity from four tropical volcanoes. Each of them tossed more than a million tons of sulfurous debris into the stratosphere, according to ice core records, where it could block sunlight and cool the surface. Gifford and his colleagues take the coincidence of the Little Ice Age's onset and massive eruptions as evidence that the one caused the other.