Average summer temperatures in the eastern Canadian Arctic are higher than they have been in at least the past 44,000 years and perhaps higher than at any time in the past 120,000 years, according to a new study.
Researchers at the University of Colorado, Boulder
say the warmth there exceeds that of the Early Holocene era, when the amount of the sun’s energy reaching the Northern Hemisphere in summer was roughly 9 percent greater than today.
“The key piece here is just how unprecedented the warming of Arctic Canada is,” said professor Gifford Miller, a fellow at CU-Boulder’s Institute of Arctic and Alpine Research who led the study. “This study really says the warming we are seeing is outside any kind of known natural variability, and it has to be due to increased greenhouse gases in the atmosphere.”
Miller and his colleagues used dead moss clumps emerging from melting ice caps on Baffin Island as tiny calendars. At four different ice caps, radiocarbon dates show the mosses had not been exposed to the elements since at least 44,000 to 51,000 years ago.
Since radiocarbon dating is only accurate to about 50,000 years and because Earth’s geological record shows it was in a glaciation stage prior to that time, the indications are that Canadian Arctic temperatures today have not been matched or exceeded for roughly 120,000 years, Miller said.
The researchers compiled the age distribution of 145 radiocarbon-dated plants in the highlands of Baffin Island that were exposed by ice recession during the year they were collected by the researchers. All samples collected were within 1 meter of the ice caps, which are generally receding by 2 to 3 meters a year.
“The oldest radiocarbon dates were a total shock to me,” said Miller.
Located just west of Greenland, the 315,999-square-kilometer Baffin Island is the fifth largest island in the world. Most of it lies above the Arctic Circle. Many of the ice caps on the highlands of Baffin Island rest on relatively flat terrain, usually frozen to their beds.
“Where the ice is cold and thin, it doesn’t flow, so the ancient landscape on which they formed is preserved pretty much intact,” Miller added.
To reconstruct the past climate of Baffin Island beyond the limit of radiocarbon dating, the team used data from ice cores previously retrieved by international teams from the nearby Greenland Ice Sheet.
The new study also showed summer temperatures cooled in the Canadian Arctic by about 5 degrees Fahrenheit from roughly 5,000 years ago to about 100 years ago – a period that included the Little Ice Age from 1275 to about 1900.
“Although the Arctic has been warming since about 1900, the most significant warming in the Baffin Island region didn’t really start until the 1970s,” said Miller. “And it is really in the past 20 years that the warming signal from that region has been just stunning. All of Baffin Island is melting, and we expect all of the ice caps to eventually disappear, even if there is no additional warming.”
A paper on the subject appeared online Oct. 23 in Geophysical Research Letters, a journal published by the American Geophysical Union.