This is a re-post from Climate Science: Roger Pielke Sr. Blog
Dr Pielke writes: Every once in a while a nugget of new research insight appears that adds to our understanding of the climate system, and its complexity. One article of this type has appeared.
Miller, G. H., et al. (2012), Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks, Geophys. Res. Lett.,39,L02708,doi:10.1029/2011GL050168
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.
The Key Points listed in the Miller et al 2012 paper are:
- Little Ice Age began abruptly in two steps
- Decadally paced explosive volcanism can explain the onset
- A sea-ice/ocean feedback can sustain the abrupt cooling
The Miller et al article is summarized HERE.
I have added the following graphic for a visual reference to the cooling and the eruptions:
Update (04-13-12: 11:00) I was look at the above graphic and I could see cold happening before the volcano eruptions, leading me to wonder if the above article has all the facts right. So did Willis Eschenbach in Guest Post at Watts Up With That: Dronning Maud Meets the Little Ice Age. Willis concludes:
I’m sorry, but I just don’t see the evidence that volcanoes had anything to do with the changes in the Baffin Island ice cap. And their whole sea/ice feedback claim? I note that the claim is supported by … well … I fear all it is supported by is models all the way down.
I recommend that you read the full post by Willis. As you can see on the graphic, there were volcano eruptions while warming was taking place, leading one to believe the volcano connection to starting the LIA are suspect. Now one could make the case they deepened the cold and misery for a few years, but not for long periods as proposed in the article. Stay Tuned, there will be more analysis to come.