Yes, indeed, we’re a couple of days late bringing you the news. But this could be an important update to our Arctic melting coverage. It’s feedback-driven (after all), American and French researchers say.
In winter the Arctic sea ice is thicker and its expanse larger. That’s why it doesn’t move much then. In summertime, the situation increasingly resembles a chaotic gyre – with a drain: Fram Strait.
That’s where the East Greenland Current flows south, carrying ice debris into the warm Atlantic.
As with climate change up north there’s more ‘summertime’ each year, ice dynamics is an actual positive feedback to sea ice melting – and one that current climate models [including the leading IPCC projection] do not take into account, say scientists of MIT and the French National Centre for Scientific Research.
It could be one of the main reasons why climate models and observed trends show such a large discrepancy.
The IPCC states the Arctic could be sea ice free during the summers at the end of the century. In reality though we’ve already had one third of the journey – and the latest melting reports only seem to show a worsening situation.
Model studies stuck to own story
There have been three consecutive studies that have all challenged the idea that the Arctic would be in a death spiral. [As a regular you may recall them: USGS | NASA | NCAR.] These studies stated the most pessimistic projections may have been exaggerating the 21st century ice loss. Melting would more likely be linear with global GHG temperature forcing, not locally feedback-driven.
Theory in a way supports these studies: the albedo feedback most often quoted as the big ice loss enhancer is a seasonal phenomenon. During the winter months sea ice could perhaps recover a bit [as there is no sun then, so reflectivity is irrelevant].
Practice however does not show this. Just last winter we’ve seen the smallest winter sea ice extent in the satellite record.
And there’s another thing about these studies: they’re all model studies – and these models the Journal of Geophysical Research publication state should first improve to better represent the complex reality of the Arctic climate system. However challenging the job, trying to better incorporate the notion that sea ice is in fact afloat on a constantly moving ocean does not seem a bad idea…
The authors show the IPCC projections have underestimated the observed decline by a factor 4. If that is indeed the size of the discrepancy we could see an ice free Arctic by September 2025 – and an ugly route towards that date.
© Rolf Schuttenhelm | www.bitsofscience.org