The so-called Little Ice Age began much earlier than originally believed, according to the conclusions of a study including at Langjökull glacier in the western highlands of Iceland in which Icelandic scientists participated.
An Icelandic glacier. Photo by Páll Stefánsson.
Four large volcanic eruptions from 1275 to 1300 started a chain reaction causing a significant cooling of the climate until the 19th century, or for 600 years, the researchers conclude, using evidence from Langjökull to support their theory.
“This is the first time that we can estimate the timing of the Little Ice Age fairly accurately, not least because we could use the year layers on the floor of Hvítárvatn lake,” Áslaug Geirsdóttir, a professor at the University of Iceland’s department of Earth Sciences, told Fréttablaðið.
The average temperature in the northern hemisphere dropped by one to two degrees (Celsius) during the Little Ice Age, which was the coldest period on earth in the past 8,000 years.
The study of the lake’s sediments—Hvítárvatn lies beside Langjökull—indicate that between 1275 and 1300 and again in 1450, the sediments were unusually thick, caused by the glacier’s above average size during that period.
Áslaug said that it wasn’t until the conclusions of the study were compared to similar research in Baffin Island and drill cores from the Greenland icecap that it became clear that the cooling wasn’t regional but extended across the entire northern hemisphere.
The four large volcanic eruptions occurred in the tropics, otherwise not much is known about them, Áslaug said.
There were also eruptions in Iceland in the period when the cooling began and they contributed to the development although they weren’t the main influential factor, she added.
Scientists have long debated when the Little Ice Age began; many mark its beginning at 1450. The reasons for the cooling have also been debated; some attribute it to volcanic eruptions, others to sunspots.
The volcanic eruptions blew an extensive amount of sulfur particles into the atmosphere which prevented the rays of the sun from reaching the earth’s surface.
This alone could only have caused a cool period of two to three years but several large eruptions also caused sea ice to spread out in the northern hemisphere which maintained the cold conditions longer than the eruptions alone would have done, Áslaug explained.