Via analysis of the snow-line elevation in the region -- a measure strongly tied to temperature -- the scientists also concluded that summer cooling occurring in Arctic Canada after the peak heat of the Holocene was much greater than predicted by climate models.
As natural variations in Earth's orbit cooled the region between 5,000 years ago and 100 years ago, summer temperatures declined by about 2.7 degrees Celsius, about twice the level predicted by global climate models known as Coupled Model Intercomparison Project Phase 5 (CMIP5).
The discrepancy between the data and the models indicates that scientists also may be underestimating how much the region will warm in the future, Miller said. Many models suggest that the Arctic Ocean will be ice-free by the end of the century, for example, while some scientists say that the ice-free threshold could be reached much sooner (ClimateWire, July 16).
Early results from additional vegetation samples gathered from sites in Greenland and Norway indicate a similar warming trend, Lehman said.
The findings are a "big deal" for showing that current temperatures are higher than the Holocene maximum, even though solar forcing was greater back then, said James Overland, an oceanographer at the National Oceanic and Atmospheric Administration who did not participate in the study.
David Pompeani, a paleoclimateologist and doctorate candidate at the University of Pittsburgh, added that the study's strength was the number of samples and the extensiveness of the radiocarbon dating.
"That is the real big kicker for me," he said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500