During the Holocene Climatic Optimum of 8,000 to 5,000 years ago, the Arctic sea ice was less than 50% [so <2.6 mln sq km] of the lowest extent on satellite record, the 2007 melting record, researchers of Copenhagen University stated on Tuesday, today reaching the news – ahead of their publication in Science.
Does this disprove ‘global warming causes the polar ice to melt’? To the contrary, as during the HCO or HTM (Holocene Thermal Maximum) it was warmer than today – in the Arctic on average about 1.6 degrees Celsius.
So, then does this study suggest the Arctic sea ice is more sensitive to warming, as such an in Arctic terms quite moderate temperature rise translates to such massive ice losses? Again no, the researchers say:
“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.”
That last one is a bit of a bold statement, because we actually remember a GCM study that had just that outcome.
It may be old news, but it would also be good news. And in the Arctic every bit of good news is welcome.
The research: driftwood does not flow
The Danes have reached their conclusions by carbon dating fossil driftwood dispersal along the northern Greenland coastline – driftwood they say can only be brought there by ice, as a journey over open sea would take the wood ‘several years’ in which time it would have sunk.
So, under that assumption, if you can on a certain location find wood from a certain period there would have been ice, if not, it would have melted and there would have been open ocean.
Let’s say it’s a creative alternative to staring to the start of the graph, 1978, when satellite measurements began, or reading the records of the ships in sailing centuries that failed to find the passage, northeast or northwest – because that is about as far as we can get: sea ice does not leave many more marks in history. Glaciers do by the way. So if the researchers could perhaps extend their Greenland fieldwork: it would be nice to how exactly the ice sheet responded to the HTM – and to compare the two.
© Rolf Schuttenhelm | www.bitsofscience.org