Volcanism alone can explain the Little Ice Age (LIA), researchers insist. Low sunspot activity is not the culprit.
Precisely dated records of ice-cap growth from Arctic Canada and Iceland show that “Little Ice Age summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430–1455 AD,” researchers found.
These intervals of sudden ice growth coincide with two of the most volcanically perturbed half-centuries of the past millennium, the study shows. “Explosive volcanism produces abrupt summer cooling at these times.”
“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.”
Once the ice age was triggered, cold summers were maintained by sea-ice/ocean feedbacks long after volcanic aerosols were removed. the authors assert. “Large changes in solar irradiance are not required.
Studies of sea ice confirmed their findings
Repeated explosive volcanism might have led to a persistent growth of sea ice during the LIA, the study found.
Sea ice does not form around Iceland; it only appears when there is a large export of sea ice from the Arctic Ocean.
Sea ice was rarely present on the North Iceland shelf from 800 AD until the late 13th Century, when a rapid increase in Arctic Ocean sea ice export shows up in the record. That was followed by another increase ∼1450 AD, after which sea ice was continuously present until the 20th Century.
The increase in sea ice north of Iceland at the start of the LIA, and its persistence throughout the LIA, supports their belief that explosive volcanism resulted in a self-sustaining sea-ice growth beginning 1275–1300 AD.
“Precisely dated records demonstrate that the expansion of ice caps after Medieval times coincided with episodes of repeated explosive volcanism centuries before the widely cited Maunder sunspot minimum (1645–1715 AD),” the researchers conclude.
“An explanation of the LIA does not require a solar trigger.”
See entire paper, entitled “Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks,” published on 31 January 2012
Thanks to iceager for this link.
“Underwater volcanoes were apparently not examined in these studies,” says Iceager.