The Little Ice Age is a period of cooling in the Northern Hemisphere which is generally thought to have lasted from around 1300-1500 to the mid-1800’s. I first became familiar with it when I read about people ice skating on the Thames and going to Frost Fairs in the 1800’s. There were 24 winters during the Little Ice Age when the Thames froze over at London and in the winter of 1683-84 it was frozen completely solid for 2 months.
Although the actual temperature change was small (perhaps 2 degrees F, varying by region,) the impact was enormous. Crop failures led to malnutrition and starvation, as well as social unrest. Glaciers advanced, in some cases destroying whole towns in their path. Diseases that thrived in cool, damp summers spread, and severe storms killed hundreds of thousands and changed coastlines.
There has been considerable uncertainty about exactly when the Little Ice Age began, how much of the Earth was involved and what the causes were. A study in Geophysical Research Letters provides some new information.
A team of scientists from the University of Colorado, Boulder, went to Baffin Island in Canada. They collected dead sea plants from the edge of the ice where they had been preserved. Radiocarbon dating showed there was a mass die-off in the years 1275-1300. That matched up with other evidence from the geologic record of a large volcanic eruption in the tropics at that time. They also did research in Iceland and looked at sediments near a glacier. The lead geologist, Dr. Gifford Miller, said, “This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age.”
They not only identified the beginning of the period, they explained how volcanic eruptions could have such a lasting effect on climate. The particles from the eruptions blocked part of the energy of the sun, which resulted in a cold snap that killed off Arctic plants and created more sea ice in the Arctic Ocean. That ice drifted south, where it melted in the Atlantic and stalled the usual ocean currents that bring warm water north. Cold water means more sea ice. Three more massive eruptions occurred within 50 years after the first to intensify the cooling. It became a self-perpetuating system that lasted hundreds of years.
More field research and climate simulations will follow. This is especially important work in light of our current climate change. It shows us how small changes in temperature can have devastating results.