Tuesday, September 4, 2012
In response to my extrapolations of sea ice volume last week, commenter Lars-Eric Bjerke noted that extrapolating trends in minimum sea ice area does not agree with extrapolating the minimum volume trends. It seems to me that if we have a scenario where the area of the ice has been shrinking steadily due to a warmer Arctic, but the ice has also been getting thinner even faster, what we would expect is that near the end, the area change would accelerate greatly as the now very thin ice breaks up.
The figure above is prepared from the minimum sea ice area according to Cryosphere today (there are various areal measures in use for Arctic sea ice but this is one of the widely used and respectable ones).
The 2012 point is my estimate of where the minimum will end up from looking at this data. Prior to 2007 (blue data), the area was shrinking at a steady and fairly linear pace. However, since 2006 (red data) the curve has fallen dramatically and consistently below the prior trend. Clearly, some new process with different dynamics has set in.
It appears to me this is consistent with the idea that the ice has now gotten thin enough in late summer to start breaking up rapidly, and that we are thus in the final phase of developing an ice free Arctic in that season. If you extrapolate the trend of the last six years, you get to zero about 2025. However, I'd set more store in the volume extrapolations (which come to zero somewhere in the 2015-2020 range), given that the area extrapolation here is based on a very short interval.
It seems likely that this will cause serious changes in the weather in the northern hemisphere, though I think climate scientists are only just starting to absorb what is happening, so the specifics of how our weather will change are probably not very clear yet.
We live in interesting times.