Wednesday, 18 March 2015

Sea ice, sea level and permafrost

Recent updates all over the place point out that Arctic sea ice levels are pretty low considering the time of year. Historically, the rate of decline of Winter Arctic sea ice cover (area, extent) is slower than that of the Summer (and the intermediate seasons). This year, the maximum so far (as pointed out at Neven's excellent blog, the finale is not yet concluded for certain, rather like a Tchaikovsky symphony) is below two standards deviation from the long term average. (here)

I don't subscribe to the notion that one season's extent is indicative of following seasons, for the simple reason that the range of inter-seasonal variability exceeds the range of climate variability. In other words, it isn't enough that there isn't much ice now to determine how much there will be at the end of this Summer (if only it was that easy!). But here we see the fortification (or continuation) of an existing and persistent trend, a reminder that we are apparently set into a pattern for the long term.

Meantime, Down South, recent observations (not yet officially published) are that the Larsen C ice shelf, thought to be stable when assessed in 2010, is now showing a big crack comparable to the one which preceded the loss of Larsen B some years back. Unlike some media, I won't publish more till the original is published, but you can check out the discussion paper at The Cryosphere.

Add to this the recent material illustrating the instability of the Totten Glacier in East Antarctica, the latest of a run of observations done in different parts of the EAIS showing a trend towards likely destabilisation (At least 4 papers recently on different glaciers).

Looking at a couple of other papers (I'll have to go find the sources at some point) I was caught by surprise when it was noted that the potential for sea level rise from the melting of permafrost is potentially very large (over time and relative to scale) and that permafrost is indeed melting reasonably rapidly across all Arctic landmasses (and, one supposes, potential under the ocean as well).

Which is all apropos of what?

One looks at a range of things and extrapolates a pattern. The apparent pattern is that a lot of the markers which might indicate an accelerated rate of sea level rise are all pointing in the same direction, and furthermore, that the observations of the changes are imminent, not down-the-line projections. For some time I've said, along with Rasmus Benestad and others, that the current 'mainstream' estimates of SLR are on the low side. 

I'd like to see a concerted effort to assess recent developments in observations and evidence as a whole and a review of the conclusions. IMO the odds of a 1 metre rise by the end of the century are now much shorter than they would have been twelve months ago. if a reader can point me to any material on the projected contribution of permafrost melting to SLR, that would be helpful, too.