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January 31 2012

Little Ice Age was caused by volcanism

Some of the iconic winter landscapes by Pieter Bruegel the Elder are more than just fine examples of sixteenth-century Dutch art. Paintings such as Bruegel’s Hunters in the Snow (1565) also serve as vivid evidence for the ‘Little Ice Age’, a period of cold climate conditions and glacier advances in Europe and elsewhere that lasted from the late Middle Ages until the nineteenth century.

There has been quite some debate over the years about the precise onset and the physical causes of this extended cold spell, with one school of thought favouring low solar activity during the ‘Maunder Minimum’ and another the cooling effect of big volcanic eruptions.

A paper published today in Geophysical Research Letters may put the solar-trigger hypothesis at rest. Gifford Miller of the University of Colorado in Boulder and his colleagues suggest that the Little Ice Age began abruptly between 1275 and 1300 AD following four large sulfur-rich explosive eruptions, most likely in the tropics, over a mere 50-year period.

Sulfate particles hurled high up into the atmosphere by the massive eruptions would have reduced the amount of sunlight reaching the ground and caused a series of cold summers. The found that ice-growth records from Baffin Island and Iceland indicate that glaciers and Arctic sea ice did advance abruptly at the time.  The resulting climate feedbacks seem to have maintained cold conditions for centuries.

“What is new in this study is that the authors have data on the growth of small icecaps in Canada and Iceland, showing a rapid increase in ice volume at the end of the thirteenth and close to the middle of the fifteenth century,” says Georg Feulner, a climate scientist at the Potsdam Institute of Climate Impact Research in Germany.

“These periods coincide with phases of strong volcanic eruptions, but a mechanism is required to produce cooling on longer timescales as the temperature drop after volcanic eruptions typically last only for a few years. In climate model simulations, the authors find that the persistent cooling observed in the climate records can be explained by expanded sea ice resulting in cooling by the ice-albedo feedback mechanism, and cooling in large parts of the North Atlantic by sea-ice export from the Arctic.”

Over at the New York Times DotEarth blog, Jennifer Francis, a climate and sea-ice researcher at Rutgers University in New Jersey, comments on the importance of the findings:

During the past several decades we have seen the enhanced warming of the Arctic owing to a variety of feedbacks involving snow, sea ice, and water vapor, but Arctic Amplification also works in the reverse direction, as in the case of the little ice age.

If a similar series of strong volcanic eruptions were to happen in the next few decades, we would likely experience global cooling with an amplified response at high latitudes. As long as greenhouse gases continue to accumulate in the atmosphere, however, the cooling can only be temporary.

Reposted fromSigalontech Sigalontech
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