Correction

By Randall Hoven

The American Thinker article, Was the Arctic Ice Cap ‘Adjusted'?, published online April 6, 2010, implied that raw sea ice data might have been adjusted for other than scientific reasons. Upon further review, all assumptions and adjustments made by NSIDC or NOAA appear justified on scientific grounds.

The article as originally published was based on a trend analysis of NSIDC's raw "area" data for northern hemisphere sea ice. The raw data do not include the "pole hole", or the zone not imaged by satellite. Since the size of the pole-hole changed significantly in 1987, any trend analysis of the raw data spanning that year is misleading.

An "update" to the article was added later, appearing online about noon on the day of publication. The update was, for the most part, technically correct, but still misleading. The update correctly noted that to account for the pole-hole, some assumption of its ice concentration must be made. But since the pole-hole is the zone nearest the North Pole, it is reasonable to assume it is nearly 100% ice in March.

The NSIDC expressed sea ice shrinkage in terms of percentage change, from the 1979-2000 mean, per decade. For "extent" that trend was -2.6% 0.7% for March. For "area" (with pole-hole included, and assuming the pole-hole is 100% ice), the corresponding trend was -2.2% 0.7%. In both cases, the trend was downward, statistically significant and about the same magnitude. (In fact, as long as the pole-hole is assumed to be at least 50% ice, the trend would be downward and statistically significant.)

This issue was addressed at Watts Up With That?

"The extent/area data is adjusted - but correctly. Comparing this to ‘CRUgate shenanigans' doesn't seem appropriate."

We concur.

Also, the article's "update" mischaracterized "area" by saying it is "the actual area of all ice sensed by satellite, whether it is part of a chunk that is at least 15% ice or not." In fact, "area" does not include those chunks with less than 15% ice.