Arctic sea ice kick started Little Ice Age in medieval Europe

Publiceret 18-09-2020
News

A comprehensive study of the prevalence and dynamics of Arctic sea ice over the last 1400 years shows that sea ice has not always been an innocent victim of climate change. It has created climate change itself, sending famine through Europe.

The ocean currents flowing down from the North along the Greenland East coast brought extreme amounts of ice with it in the beginning of the 1400th century. (Illustration: Schmith et al. 2003 (historic map), large map modified from Miles et al. 2020)

Around the year 1300, an unusually cold period known as The Lille Ice Age began, stretching all the way to around 1850. This mysterious era have been subject of extensive research during the years, since we do not fully understand what caused it.

What we do know is that it was not a global phenomenon but rather a trend where some larger areas in turn experienced decades of extreme cold, harsh winters followed by unusually cold, short summers. Therefore, the overall drop in global temperature was below 0.5° C, but locally the cold is was more than enough to put its mark on both nature and history books, causing failed harvest and famine throughout Europe.

Now, a team of researchers with participation from GEUS has managed to uncover one of the culprits. The Arctic sea ice.

”We looked north to investigate a theory regarding sea ice from the Arctic Ocean playing an important role in kick starting the Little Ice Age. Out results show that the sea ice was in fact of great importance for the onset of the cooling,” says paleoclimatologist at GEUS Camilla S. Andresen.   

More ice leaving the Arctic

Both now and then sea ice is flowing along the East and South coast of Greenland, forming in the North and carried southwards from there by ocean currents.

To determine whether changes in this transport of ice out of the Arctic was linked to the onset of the Little Ice Age, the researchers collected and joined all reconstructions and models made on changes in sea ice in the past using data from seafloor cores. An approach that has not been done before.    

”We were thrilled when the analysis showed a very clear result,” Camilla S. Andresen says. “Around 1300 years ago, the transport of sea ice from the Arctic suddenly increased immensely compared to the previous centuries, where the transport had been smaller and steadier.”

It is normal for the Arctic sea ice to deviate from one year to another, but the surge in the beginning of the 1400th century was undoubtedly not normal, she explains. This was a dramatic increase in ice leaving the Arctic and flowing southwards lasting for decades, peaking in the middle of the century and then going slowly back to normal towards the year 1400. According to the researchers, this would mean increasing amounts of ice and meltwater along the southern coast of Greenland and in the North Atlantic in most of the century. The analysis showed that it even stayed elevated for a long time.   

Iceberg

Photo: Robert Fausto, GEUS

Climate change as dominos

However, it is not only the ice itself causing the cooling back then, researchers explain. It is what the ice brings with it. Cooled freshwater. In huge quantities.

”All this cold freshwater could very well have disturbed the Gulfstream, that brings us the mild winters here in Northern Europe. Too much freshwater poured into the currents changes how they work,” Camilla S. Andresen explains.

Furthermore, the climatic effects of the Gulfstream are not limited to Northern Europe. It connects the Arctic with the rest of the world through the global pattern of ocean currents intertangling with one another. Also known as the thermohaline circulation. Changed in the climate regionally due to changes in the Gulfstream could therefore create changes throughout the entire planet.

There is no doubt, according to the paleoclimatologist that sea ice potentially holds an important role as one of the first pieces in the climatic row of Dominos. Therefore, it is crucial to understand how climate change affect the Artic if we are to predict the consequences of the current climate situation and the effect it might have on the entire, global climate system, she says.