The study, led by University of Colorado-Boulder geological sciences Professor Gifford Miller, used dead moss clumps emerging from receding ice caps on Canada's Baffin Island as tiny clocks, with radiocarbon dating showing they had not been exposed to the elements by ice melt since at least 44,000 to 51,000 years ago.
Since Earth was in a long glaciation period prior to that time, it means Canadian Arctic temperatures today likely have not been matched or exceeded for roughly 120,000 years, Miller said.
"The key piece here is just how unprecedented the warming of arctic Canada is," he said. "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."
Temperatures across the Arctic have been rising substantially in recent decades as a result of the buildup of greenhouse gases in Earth's atmosphere, the researchers said.
Previous studies by CU-Boulder scientists in Greenland found temperatures on the ice sheet have climbed 7 degrees Fahrenheit since 1991.
"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," Miller said. "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."