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News July 2012

Cryosat 2 versus PIOMAS

on Monday, February 18, 2013

The recent Cryosat 2 results bear examination against PIOMAS in terms of what new information is presented with respect to diminishing Arctic ice volume.

From the paper published:

http://www.personal.soton.ac.uk/pgc1g08/grl50193.pdf

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.


This states that for the summer time minimum volume PIOMAS is rather optimistic and for the winter time maximum volume it is rather pessimistic.

This should not come as a great surprise as the PIOMAS site itself states a significant margin of error (in proportion to the remaining ice volume) and a bias in measuring thin ice to be thicker and thick ice to be thinner.

The implications of this bear pointing out however - as PIOMAS exponential fit - well followed to date - predicts the zero axis for ice volume will be crossed for the minimum between 2014 and 2015, which is of course impossible, since the minimum occurs at the end of the melt season, not in the winter. Therefore 2014 is a real possibility, with 2015 rather likely.

However, with Cryosat 2 confirming that PIOMAS overestimates thin ice - I would suggest 2014 becomes far more likely, with risks of massive loss in 2013 therefore higher. This graph is prepared from PIOMAS data:

http://neven1.typepad.com/.a/6a0133f03a1e37970b017d3ebb6764970c-pi

Note the significant drop for 2010 compared to prediction, and then note that the error bars - based on PIOMAS data - cross the zero axis in 2013 (albeit not by a lot). The projection is a loss of another 1000km^3 this year.

It should also be noted that observations suggest a high rate of fracturing occurring in the winter ice currently, suggesting it to be rather thin and flimsy. Aside from the hope that this will increase the freezing rate slightly - it should be noted that PIOMAS is tracking a surprisingly low volume of ice as we approach the winter maximum volume:

http://psc.apl.washington.edu/wordpress/wp-content/uploads/schweiger/ice_volume/BPIOMASIceVolumeAnomalyCurrentV2_CY.png

The graph doesn't show it ideally well, but typically the loss of winter maximum volume has proceeded more slowly than the loss of summer minimum. It is rather more serious therefore if the initial condition includes a relatively large loss of winter maximum volume.

The more time any plan assumes on having - the bigger a gamble it is. The stakes we are gambling for are rather high and prudence dictates the desirability of the best odds obtainable.