* Posts by Clarence

2 publicly visible posts • joined 19 Aug 2008

Arctic ice refuses to melt as ordered

Clarence

The difference is in the 2007 data

CT had much less ice extent than NSIDC in mid-August last year, while this year's data are very similar.

Compare http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/ARCHIVE/20070812.jpg and ftp://sidads.colorado.edu/pub/DATASETS/seaice/polar-stereo/nasateam/final-gsfc/browse/north/daily/2007/nt_20070812_f13_v01_n.png

I made an overlay of both, as far as possible due to different map projections: http://i36.tinypic.com/nxjteb.png

MODIS image of the eastern Beaufort Sea at that day: http://rapidfire.sci.gsfc.nasa.gov/realtime/single.php?T072240405 (cloudy elsewhere).

CT images had much fluctuations from day to day at that time; NSIDC images were much more stable. The increase between 2007-08-12 and 2008-08-11 in extent based on CT images is indeed somewhere in the range 20-40 %, but comparing single days doesn't make much sense with that much daily fluctuation (apart from the questionable method of pixel counting in anti-aliased and distorted images).

Clarence

@Jeff

CT obviously uses NCEP data with some coastal noise removed. Compare with NCEP images from (nominal) 1 day before:

http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/ARCHIVE/20080811.jpg ftp://polar.ncep.noaa.gov/pub/history/ice/nh/nh12.20080810.gif

http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/ARCHIVE/20080818.jpg ftp://polar.ncep.noaa.gov/pub/history/ice/nh/nh12.20080817.gif

BTW, NSIDC doesn't seem to have an archive of daily images, but they do have the image of 366 days before:

http://nsidc.org/data/seaice_index/images/daily_images/N_daily_concentration.png http://nsidc.org/data/seaice_index/images/daily_images/N_record_concentration.png

And note that NSIDC (and others) doesn't use an equal area projection, so pixel counting isn't quite correct (raw data needs to be weighted too to be exact).

The reason that NSIDC reports a relatively small difference in extent between 2007 and 2008 may be high amounts of coastal noise, and the provisional data of 2008 seems to have less of it. So the real difference in extent is likely to be greater. But the difference in area is smaller, and the remaining ice seems to be in an even poorer state than in 2007.

The current rate of decline is notable at this time of the year, and almost all ice melted within the Arctic. The export through Fram Strait has been almost zero during the last weeks.