Arctic temperatures at 44,000-year high because of greenhouse gases

The average summer temperature in the eastern Canadian Arctic is higher than in any previous century in the past 44,000 years — and perhaps the highest in 120,000 years — reflecting what scientists call an unprecedented warming of the region due to climate change, according to a new study by the University of Colorado, Boulder.

"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," Gifford Miller, a study leader, said in a joint statement from the school and the publisher of the journal Geophysical Researcher Letters, which published the findings this week.

The study, according to the statement, presents the first direct evidence that the present warmth in the Canadian Arctic exceeds the peak warmth there when Earth's last glacial period ended, about 11,700 years ago. In the early stages of that period, the amount of the sun's energy reaching the Northern Hemisphere during summer months was roughly 9 percent greater than today, causing world sea levels to rise about 115 feet.

Researchers took dead moss clumps from receding ice caps on Baffin Island, the world's fifth-largest island, west of Greenland, and used them as tiny clocks to measure the ice caps' warming rate. Scientists then looked at the age distribution of 145 radiocarbon-dated plants that had been exposed by ice recession during the year they were collected.

Radiocarbon dates from four ice caps from the highlands of Baffin Island showed that the last time the mosses had been exposed to the elements was at least 44,000 to 51,000 years ago. 

Since radiocarbon dating is accurate to only about 50,000 years and because Earth was in a glaciation stage before then, the implications are that Canadian Arctic temperatures today have not been matched for nearly 120,000 years, said Miller.

"The oldest radiocarbon dates were a total shock to me," he said in the release.

The study also showed summer temperatures cooled in the region by about 5 degrees Fahrenheit roughly from 5,000 years ago to 100 years ago. 

"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."

In recent decades, temperatures across the Arctic have been rising significantly as a result of the buildup of greenhouse gases in Earth's atmosphere. Previous studies by CU Boulder researchers in Greenland indicate temperatures on the ice sheet have climbed 7 degrees Fahrenheit since 1991.

Al Jazeera and wire services