Gifford H Miller, Aslaug Geirsdottir, Yafang Zhong, Darren J Larsen, Bette L Otto-Bliesner, Marika M Holland, David Anthony Bailey, Kurt A. Refsnider, Scott J. Lehman, John R. Southon, Chance Anderson, Helgi Björnsson, and Thorvaldur Thordarson, Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks, Geophysical Research Letters, doi:10.1029/2011GL050168 (30 January 2012) (in press, as of this writing)
What the study found
Ice dating from Iceland and Arctic Canada demonstrate that the Little Ice Age’s summer cold and ice growth began between 1275 and 1300. Cold intensified in 1430 to 1455. And, according to the ice cores, these periods corresponded with increased volcanism.
The authors calculated that Little Ice Age conditions began with four explosive eruptions, over fifty years. Each eruption ejected 60 teragrams (60 x 1012 grams) of sulfates into the atmosphere.
Sulfate aerosols produced summer cooling, which was maintained by sea-ice (and presumably cold water) feedback. The positive feedback maintained these cold summer conditions, even after the cooling aerosols fell out of the atmosphere.
Caveat — dates for the duration of the Little Ice Age are disputed
The authors’ abstract suffers from failing to define what they mean by the term, Little Ice Age.
Perhaps access to the full length article would clear that question up. But it’s a pity they didn’t explain what they were referring to in the abstract, where the definition properly belongs.
Wikipedia’s overview, which matches my recollection of the historical use of the term, indicates that the period is variously defined as extending from 1300 to 1850 AD.
Presumably the post-1300 cooling caught people’s attention because it followed the Medieval Warm Period/Climate Optimum (950 to 1250).
However, the research team’s volcanic eruption mechanism (as reported in the abstract) and abrupt ice growth period refers only to the 1275 to 1455.
So, one wonders whether their postulated ice-feedback mechanism could have lasted for another four hundred years, long after sulfate aerosols were flushed from the atmosphere.