Boulder – Between 1275 and 1300 A.D  the Earth experienced widespread cooling known as the Little Ice Age.  Now, research led by the University of Colorado Boulder, with co-authors at the National Center for Atmospheric Research (NCAR) and other organizations, has come up with a new theory that the Little Ice Age could have been triggered by volcanic activity.  Details of the study were recently published in Geophysical Research Letters.

During the study, researchers analysed patterns of dead vegetation, ice and sediment core data.  Using alongside computer based climate models, this allowed the researchers to discover new evidence in to the causes of the Little Ice Age.  Computer simulations show that the cold period could be explained by the expansion of the sea ice and the related weakening of the Atlantic currents.

Previous theories into the Little ice Age had suggested that it had been triggered by a decrease in summer solar radiation, volcanic eruptions that had a cooling effect on the planet by releasing sulfates or possibly a combination of the two.

Lead author Gifford Miller of the University of Colorado Boulder, 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.”

“We also have provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time. If the climate system is hit again and again by cold conditions over a relatively short period—in this case, from volcanic eruptions—there appears to be a cumulative cooling effect.”

NCAR scientist Bette Otto-Bliesner, a co-author of the study, said:

“Our simulations showed that the volcanic eruptions may have had a profound cooling effect.”

“The eruptions could have triggered a chain reaction, affecting sea ice and ocean currents in a way that lowered temperatures for centuries.”

Scientists estimate say that the Little Ice Age began from the 13th-16th century but there is no firm agreement on this.  As part of the research, Miller and his team carbon dated approximately 150 samples of plant material which were collected from Baffin Island in the Canadian Arctic.  The researchers discovered a large amount of “kill dates” between 1275 and 1300 A.D., researchers say that this shows that the plants had been “had been frozen and engulfed by ice during a relatively sudden event”.

Researchers then analysed sediment cores from a glacial lake in Iceland which is related to a 367-square-mile Langjökull ice cap.  The annual layers in the core were dated by using the tephra deposits  from volcanic eruptions in Iceland dating back more than 1,000 years.  The researchers say that it became thicker in the 13 century and in the 15th century.

Miller said:

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

“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.”

Researchers then used the Community Climate System Model, a system developed by  the NCAR, the Department of Energy and other organisations.  The computer system was used to assess the “effects of volcanic cooling on Arctic sea ice extent and mass”.  The computer model showed that several large volcanic eruptions could have the Northern Hemisphere significantly enough to trigger the expansion of the Atlantic sea ice.

However, there are other theories regarding the Little Ice Age such as the one from researchers Stanford University which theorised that the Little Ice Age could have been caused by deforestation.

 

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