Tuesday, September 4, 2012

Collapse in Minimum Arctic Sea Ice Area

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.


vdansk said...

So...taking the less scary, probably less accurate prediction of 2025, any idea how many people will be displaced and how many acres of arable land lost from resultant increases in sea levels by that time?

Stuart Staniford said...


Loss of sea ice has no effect on sea level (since it floats it displaces only it's own mass in sea water). Presumably, loss of sea ice accelerates melting of the Greenland ice sheet to some unknown degree, but still it's unlikely to have a truly dramatic effect before 2025.

The issue is rather that having a bunch of (comparatively) warm water up in the arctic, instead of ice, in the fall is likely to have a significant effect on the atmospheric circulation, and to dump a lot of extra moisture into the top of the planetary atmosphere (presumably making for snowier winters somewhere).

dcomerf said...

Eh..? None: melting sea ice doesn't cause sea level to rise. It will cause a warmer Arctic though (through increased heat absorbtion of ocean water relative to ice), which is not good news for the Greenland ice sheet.

Lucas Durand said...

"...so the specifics of how our weather will change are probably not very clear yet."

Though I'm sure climate scientists will do their best, I wouldn't put too much faith in any "specifics" about how the weather will be effected.

Let's not forget that what we have seen in the arctic this year is a lesson in failed predictions.

We do live in interesting times and part of what makes them so interesting is that we really have no idea what might happen next - we should all be expecting the unexpected.

Dan said...

Wouldn't a reduction of the Greenland ice sheet give us a double whammy where the melting ice first raises the sea leavel, then crystal rebound raising the littoral regions displaces even more?