Much concern has been made about the dramatic drop in Arctic sea ice levels over the past decade, but new research out of Denmark suggests that the extent of the Arctic sea ice is extremely variable.
The research was published in the journal Science and authored by Svend Funder, Eske Willerslev and Kurt Kjær, all associated with the Danish Research Foundation at the University of Copenhagen.
This is the first time that an idea of past sea ice levels has been extracted from the region. Recent sea ice levels have been determined using satellites, ships and planes, but prior to the introduction of such technology, there had been no manner in which to properly map out the extent of the sea ice. Additionally, sea ice does not tend to leave a lot of proof behind of its existence.
“Our key to the mystery of the extent of sea ice during earlier epochs lies in the driftwood we found along the coast,” said Funder. “One might think that it had floated across sea, but such a journey takes several years, and driftwood would not be able to stay afloat for that long. The driftwood is from the outset embedded in sea ice, and reaches the north Greenland coast along with it. The amount of driftwood therefore indicates how much multiyear sea ice there was in the ocean back then. And this is precisely the type of ice that is in danger of disappearing today.”
“Our studies show that there have been large fluctuations in the amount of summer sea ice during the last 10,000 years,” Funder added. “During the so-called Holocene Climate Optimum, from approximately 8000 to 5000 years ago, when the temperatures were somewhat warmer than today, there was significantly less sea ice in the Arctic Ocean, probably less than 50% of the summer 2007 coverage, which is absolutely lowest on record.
“Our studies also show that when the ice disappears in one area, it may accumulate in another. We have discovered this by comparing our results with observations from northern Canada. While the amount of sea ice decreased in northern Greenland, it increased in Canada. This is probably due to changes in the prevailing wind systems. This factor has not been sufficiently taken into account when forecasting the imminent disappearance of sea ice in the Arctic Ocean.”
The team also looked at the remnants left by ancient beaches. Traditionally, there are no beaches on the northern coasts of Greenland, as the ice prevents them. But there are beach ridges to be found that prove waves once crashed onto the land with no ice to hinder them.
The ridges were mapped for 500 kilometres along the coast, and dated back to a warm period that existed between 8000 until 4000 years ago, when there was more open water and less coastal ice than there is today.
“Our studies show that there are great natural variations in the amount of Arctic sea ice,” said Funder. “The bad news is that there is a clear connection between temperature and the amount of sea ice. And there is no doubt that continued global warming will lead to a reduction in the amount of summer sea ice in the Arctic Ocean.
“The good news is that even with a reduction to less than 50% of the current amount of sea ice the ice will not reach a point of no return: a level where the ice no longer can regenerate itself even if the climate was to return to cooler temperatures.
“Finally, our studies show that the changes to a large degree are caused by the effect that temperature has on the prevailing wind systems. This has not been sufficiently taken into account when forecasting the imminent disappearance of the ice, as often portrayed in the media.”
Source: University of Copenhagen