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April 15th, 2012 
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Climate Fact Of The Day – Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks
GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L02708, 5 PP., 2012
doi:10.1029/2011GL050168
Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks
Authors:
Gifford H. Miller – INSTAAR and Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA
Áslaug Geirsdóttir – Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland
Yafang Zhong – INSTAAR and Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA
Darren J. Larsen – INSTAAR and Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA
Bette L. Otto-Bliesner – National Center for Atmospheric Research, Boulder, Colorado, USA
Marika M. Holland – National Center for Atmospheric Research, Boulder, Colorado, USA
David A. Bailey – National Center for Atmospheric Research, Boulder, Colorado, USA
Kurt A. Refsnider – INSTAAR and Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA
Scott J. Lehman – INSTAAR and Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA
John R. Southon – Earth System Science Department, University of California, Irvine, California, USA
Chance Anderson – INSTAAR and Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA
Helgi Björnsson – Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland
Thorvaldur Thordarson – School of GeoSciences, University of Edinburgh, Edinburgh, UK
Abstract:
Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes. However, the causes of superposed century-scale cold summer anomalies, of which the Little Ice Age (LIA) is the most extreme, remain debated, largely because the natural forcings are either weak or, in the case of volcanism, short lived. Here we present precisely dated records of ice-cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430–1455 AD.
Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. A transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. Our results suggest that the onset of the LIA can be linked to an unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading 60 Tg. The persistence of cold summers is best explained by consequent sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required. Read Paper
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