Little Ice Age Started With Volcanoes

In the late 13th century, massive volcanic explosions in the tropics destroyed mountain villages in northern Europe—not by burying them in lava and mudflows, mind you, but by triggering a cold spell that engulfed the towns in ice.

So goes the latest explanation for the underlying cause of a celebrated cold snap known as the Little Ice Age. Famous paintings from that period depict ice skaters on the Thames River in London and canals in the Netherlands, two places that were ice-free before then and have been so ever since.

Scientists had long known that the Little Ice Age started sometime after the Middle Ages and lasted for centuries. But estimates of its onset have ranged from the 13th to the 16th century, and arguments have raged over the cause.

Now a team of geologists led by Gifford Miller of the University of Colorado, Boulder, has identified an abrupt start for the cool spell, sometime between 1275 and 1300 A.D. Repeated, explosive volcanism cooled the climate and set off a self-perpetuating feedback cycle involving sea ice in the North Atlantic Ocean that sustained the cool spell into the 19th century, they reported this week in the journal Geophysical Research Letters.

“This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age,” Miller said in a press release. “We also have provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time.”

In the first part of the study, Miller and his colleagues collected roughly 150 dead plants from the receding ice margins of Baffin Island in the Canadian Arctic (see photograph above). Radiocarbon dating back in the lab reveled a large cluster of “kill dates” between 1275 and 1300 A.D., indicating the plants had been frozen and engulfed by ice during a relatively sudden event.

Only major volcanic eruptions could cool the climate that quickly, Miller’s team surmised, by kicking up particles that block some of the sun’s incoming energy. The timing jibed with a period of intense volcanic activity already known from the rock record, but they knew those ejected particles would have dissipated too quickly to sustain cooler temperatures for the full duration of the Little Ice Age.

The team used climate simulations to see what else might have been going on, combining feedback patterns known to have occurred in the ocean. Think of it as a step-by-step guide to how volcanoes in the tropics could engulf northern European towns in ice:

1. A massive volcanic eruption rocks the tropics between 1275 and 1300 A.D.
2. The eruptions cloud the skies across the northern hemisphere with shiny particles, called aerosols, that block some of the sun’s incoming energy.
3. A cold snap ensues, killing off low-lying and higher elevation Arctic plants in one fell swoop.
4. The volcano-induced cooling generates extra sea ice in the Arctic Ocean.
5. Some of that sea ice makes its way south along the eastern coast of Greenland, melts in the North Atlantic Ocean, and stalls the ocean circulation patterns that usually send warmer waters back north.
6. Water up north stays cold instead, sustaining the enlarged areas of sea ice.
7. Within a 50-year period, three more massive eruptions intensify the cooling trend.
8. The feedback cycle that sustains the sea ice perpetuates the colder regional climate for decades after the last of the volcanic aerosols rain out of the sky.
9. With a volcano-induced cold spell now persisting for centuries, mountain glaciers in Norway and the Alps advance into inhabited valleys, destroying towns.

That’s it in a nutshell

Read more at Discovery News