Summer temperatures in the eastern Canadian Arctic have likely been warmer over the last 100 years than in any century in the last 120,000 years, according professor Gifford Miller, leader of a recently released University of Colorado study on the topic.

Miller, a professor of geological sciences at CU, and his colleagues on the study traveled to Baffin Island, the icy landmass located primarily above the Arctic Circle just west of Greenland, between 2005 and 2010 to perform research for the project, he said.

According to a news release issued by CU, the research team performed carbon dating on clumps of dead moss uncovered by receding ice caps on the 196,000-square-foot island to determine when the last time temperatures similar to those being experienced now were seen there. Using that information, and comparing it with data from previously retrieved ice cores from the nearby Greenland Ice Sheet, Miller and his team determined it had been at least 44,000 years, and perhaps as long as 120,000 years ago, according to the release.


That research, detailed in a paper that appeared online Wednesday in Geophysical Research Letters, is the first direct evidence that present temperatures in the east Canadian Arctic exceed those of the early Holocene epoch, according to Miller. The Holocene is Earth's current epoch that began when the last glacial period ended about 11,700 years ago. In the early stages of the period, the Northern Hemisphere was closer to the sun and received about 9 percent more solar energy in summers than it does today, Miller said.

"It should have been getting colder ... but suddenly that has been reversed in the last century," said Miller, who is also a fellow at CU's Institute of Arctic and Alpine Research. "This is the first study to show that we have exceeded that early Holocene peak."

Miller said radioactive dating is limited because after about 50,000 years the radioactive element being measured has faded so significantly. The research team knew that the Earth was in the middle of an ice age 44,000 to 50,000 years ago and it was unlikely Baffin Island was experiencing warm temperatures then, thus the use of the Greenland Ice Sheet records.

"If you then look at the Greenland record, the most realistic time when temperatures were even vaguely close to present was at the end of the last interglaciation," Miller said, referring to the period between ice ages last experienced about 120,000 years ago. "It's not hard data, but that is the most reasonable estimate."

Because the eastern Canadian Arctic region is receiving less solar energy than it was in the early Holocene, and the last known record of similar temperatures was so long ago, Miller said he is confident in ruling out natural variability as the reason for the warmer summers. He attributes the temperature rise to increased greenhouse gases in the atmosphere, especially over the past 40 years.

"It's reasonable to ask whether some of that warming is natural variability, and that is what we have been able to exclude with this study," Miller said. "It really adds to that growing consensus that those greenhouse gas increases are responsible for the contemporary warmth."

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