As ClimateProgress and others report, initial results are in from Cryosat-2. Since 2010, this European Space Agency satellite has surveyed polar ice to estimate its thickness, and by extension, its volume. It was a replacement for Cryosat-1, which was unfortunately destroyed in a launch failure. But the European Space Agency (ESA) considered this mission important enough to construct and deploy a replacement promptly, approving Cryosat-2 less than five months after the failure of Cryosat-1.



Initial results are now published in CryoSat-2 estimates of Arctic sea ice thickness and volume (Laxon et al., GRL, doi:10.1002/grl.50193). They compare estimates of Arctic sea ice volume during the Cryosat-2 period (2010 through 2012) to those during the ICESAT period (2003 through 2008), and to model results from PIOMAS, confirming that the stunning ice loss indicated by PIOMAS data is real. The abstract highlights this fact:



Between the ICESat and CryoSat-2 periods the autumn volume declined by 4291 km3 and the winter volume by 1479 km3. This exceeds the decline in ice volume in the central Arctic from the PIOMAS model of 2644 km3 in the autumn, but is less than the 2091 km3 in winter, between the two time periods.



It’s most interesting that the Cryosat-2 ice loss estimate during autumn is so much larger (by 1647 km^3, 62%) than the PIOMAS estimate, but the winter loss is quite a bit less (by 612 km^2, 71%). PIOMAS data already indicated that the annual cycle of ice volume has increased its amplitude, but the Cryosat-2 data suggest an even more dramatic change in the size of the annual cycle than that estimated by PIOMAS.

Cryosat-2 also indicates considerable ice volume decrease between winter 2011 and winter 2012, which they suggest may have been a contributing factor in the astoundingly low sea ice extent and volume observed at the 2012 September minimum. PIOMAS indicates no such winter decline from 2011 to 2012, although it does record the record low 2012 minimum. PIOMAS also suggests a decline between winter 2012 and this winter 2013. That could mean several things. It could presage another record minimum this coming September (I haven’t yet seen the Cryosat-2 estimates for winter 2013). Or it could mean that PIOMAS is simply “catching up to reality,” indicating the winter decline during 2013 rather than 2012 as shown by Cryosat-2. It could even mean that there is some undetected bias or uncertainty in the Cryosat-2 results, and that PIOMAS is more correct. And of course, it’s possible that the winter decline in 2012 isn’t really related to the 2012 record low minimum. Time will tell.

Cryosat-2 does indicate consistently higher ice volume than PIOMAS, typically around 20% during Autumn (Oct/Nov) and 10% during Winter (Feb/Mar).

Despite the bias between the two estimates, the decline is quite clear — and yes, properly described as “stunning.”

Another view of the sharp decline between Winter 2011 and 2012 levels in Cryosat-2 data, which is not seen in PIOMAS data, is this direct comparison of their estimates (Cryosat-2 data shown as triangles, PIOMAS estimates as circles):

Given the limited data available to calibrate ice thickness up to now, the Cryosat-2 results are a testament to the ingenuity of the PIOMAS team. Their model results gave decent estimates of ice volume, and their clearest result — the stunning loss of sea ice volume in the Arctic — is now confirmed. I expect the PIOMAS model soon will be revised by incorporating the results of Cryosat, and a newer, even more accurate, model estimate to be made available, one which has the advantage of covering more than three decades.

I also expect Arctic sea ice volume — and area, extent, and thickness — to continue to decline. Sea ice in the Arctic is warning us. Our climate, our planet, is changing and will continue to change. We’re not gonna like the result.

Click the graph!

UPDATE

As a reader pointed out, in the first graph the data labelled “Cryosat-2” are actually from ICESAT (the first data points) and from Cryosat-2 (the later data points).