Massive volcanic eruptions may have triggered Little Ice Age

Washington, Jan 31 (ANI): Researchers have shed new light on the onset and cause of Earth's Little Ice Age, a period of cooling temperatures that began after the Middle Ages and lasted into the late 19th century.

According to the new study, the Little Ice Age began abruptly between A.D. 1275 and 1300, triggered by repeated, explosive volcanism and sustained by a self- perpetuating sea ice-ocean feedback system in the North Atlantic Ocean, according to CU-Boulder Professor Gifford Miller, who led the study.

While scientific estimates regarding the onset of the Little Ice Age range from the 13th century to the 16th century, there is little consensus, said Miller.

There is evidence the Little Ice Age affected places as far away as South America and China, although it was particularly evident in northern Europe.

Advancing glaciers in mountain valleys destroyed towns, and famous paintings from the period depict people ice-skating on the Thames River in London and canals in the Netherlands, waterways that were ice-free in winter before and after the Little Ice Age.

"The dominant way scientists have defined the Little Ice Age is by the expansion of big valley glaciers in the Alps and in Norway," said Miller.

"But the time it took for European glaciers to advance far enough to demolish villages would have been long after the onset of the cold period," said Miller, a fellow at CU's Institute of Arctic and Alpine Research.

The new study suggests that the onset of the Little Ice Age was caused by an unusual, 50-year-long episode of four massive tropical volcanic eruptions.

Climate models used in the new study showed that the persistence of cold summers following the eruptions is best explained by a sea ice-ocean feedback system originating in the North Atlantic Ocean.

As part of the study, Miller and his colleagues radiocarbon-dated roughly 150 samples of dead plant material with roots intact collected from beneath receding ice margins of ice caps on Baffin Island. There was a large cluster of "kill dates" between A.D. 1275 and 1300, indicating the plants had been frozen and engulfed by ice during a relatively sudden event.

Both low-lying and higher altitude plants all died at roughly the same time, indicating the onset of the Little Ice Age on Baffin Island - the fifth largest island in the world was abrupt. The team saw a second spike in plant kill dates at about A.D. 1450, indicating the quick onset of a second major cooling event.

To broaden the study, the team analyzed sediment cores from a glacial lake linked to the 367-square-mile Langjokull ice cap in the central highlands of Iceland that reaches nearly a mile high. The annual layers in the cores-which can be reliably dated by using tephra deposits from known historic volcanic eruptions on Iceland going back more than 1,000 years suddenly became thicker in the late 13th century and again in the 15th century due to increased erosion caused by the expansion of the ice cap as the climate cooled, he said.

"That showed us the signal we got from Baffin Island was not just a local signal, it was a North Atlantic signal," said Miller.

"This gave us a great deal more confidence that there was a major perturbation to the Northern Hemisphere climate near the end of the 13th century," Miller added.

The team used the NCAR-based Community Climate System Model to test the effects of volcanic cooling on Arctic sea ice extent and mass. The model, which simulated various sea ice conditions from about A.D. 1150-1700, showed several large, closely spaced eruptions could have cooled the Northern Hemisphere enough to trigger Arctic sea ice growth.

The study has been published in Geophysical Research Letters, a publication of the American Geophysical Union. (ANI)