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 with the abstract [highlight added]
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
“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.”
Although Wiki is not always the most reliable source, it seems to be fairly accurate on non-controversial topics, such as the history of major volcanic eruptions.
http://en.wikipedia.org/wiki/List_of_large_volcanic_eruptions
There was apparently a large (VEI 7) event in 1258 CE, and a smaller (VEI 6) event in 1280 CE. No other large eruptions until another VEI 6 in 1452-3.
Considering the nature of large volcanic events, I would expect better coincidence of timing if they caused or triggered the LIA.
In June 1991 Mount Pinatubo blew up in the Philipines and sent 30 billiion cubic meters of junk into the atmosphere. This caused global cooling of about 1 degrees C for two years. This was the largest volcano erruption of the 20th century
I checked the University of Illinois data on sea ice and essentially saw no chang e in Arctic sea ice for the period 1992-1994. I am wondering about this hypothesis. Of course the volcano explosions back in the 15 the century may have been a lot bigger.