The study, published in the journal Nature, examined tree rings, ice cores from glaciers and sediments. Overall, the researchers combined 69 different data sources to determine the extent of sea ice for every decade going back 1,000 years and every 25 years beyond that.
They worked to create a detailed reconstruction of sea ice over the past 1,450 years. This is the first attempt to reconstruct sea ice coverage for the Arctic region over such a long period of time.
“The recent sea ice decline which has been well documented during mostly the period of satellite observations looks like its unprecedented in terms of how sustained it has been,” Christian Zdanowicz of the Geological Survey of Canada tellsThe Weather Network.
“It also seems to have reached a point where the sea ice now, according to our reconstruction, is as small as it’s ever been in the last 1,450 years,” says Zdanowicz, who co-authored the study. “It has really shrunk to a record low.”
Climate change is thought to be occurring in the Arctic faster than anywhere else on Earth, and sea ice is considered to be one of the main indicators. The ice is especially crucial in this area, because it acts as an environment for many species ranging from polar bears to plankton.
Zdanowicz says that sea ice decline is very cyclical. If there is less ice, it means that more solar heat is absorbed by the ocean, because it’s not reflected back to space by sea ice. “So you have a warmer Arctic Ocean, and that means it will be more difficult to establish an extensive sea ice coverage the next season,” he explains. “That effect just sort of carries over year after year.”
“The warmer the ocean gets, the less sea ice. The less sea ice, the warmer the ocean gets.”
Zdanowicz says that while the research was not specifically an “attribution” paper, it’s difficult to conclude that only natural factors are contributing to the sea ice decline.
“The paper itself is not really an attribution paper, in the sense that we don’t end up with a smoking gun that could tell us, ‘Ok, it’s either this or that,’” he says.
“It’s difficult to account for such a dramatic change without adding to the equation the effect of greenhouse gas warming. It doesn’t prove it in an unequivocal fashion, but it certainly points in that direction.”
Previously, Zdanowicz was involved in another paper studying Arctic sea ice decline. That paper went back 10,000 years. In it, he found that thousands of years ago, sea ice was also quite low.
“At the end of the last ice age, there was a period of several thousand years where the summer climate in the Arctic and Subarctic latitudes were actually warmer than they are now,” he says. “But that can be accounted for by the fact that at the time, these regions were receiving slightly more energy than they are now, for orbital reasons.”
He went on to explain that the Northern hemisphere was receiving more solar energy, because of the Earth’s orbit.
Zdanowicz says that due to these orbital fluctuations, there is good reason to think that between 8,000 and 10,000 years ago, there were parts of the Arctic Ocean and the Arctic islands that had less sea ice coverage than present day.
“But this mechanism can not account for what’s happening now,” he says.
“If only orbital cycles were at play here, we should slowly be edging our way towards the next glacial cycle.”
With files from the Associated Press