Reply #21: Thanks

[The Croquist]

Like I said, I only knew back to 1979. It is actually a combination between the satellite data (that I mentioned in my earlier post) from 1980 to present and from 1953 - 1979 from Hadley.

Mean sea ice anomalies, 1953-2009: Sea ice extent departures from monthly means for the Northern Hemisphere. For January 1953 through December 1979, data have been obtained from the UK Hadley Centre and are based on operational ice charts and other sources. For January 1979 through July 2009, data are derived from passive microwave (SMMR / SSM/I). Image by Walt Meier and Julienne Stroeve, National Snow and Ice Data Center, University of Colorado, Boulder

It's interesting that they waited a year before switching to their own (NSIDC) data. I'm sure they have a good reason.

I've got to wonder about the quality of the Hadley data. I'm sure it is the best they could do, but without satellites how did they measure it? I would guess military flights and nuclear submarine measurements but the coverage had to be spotty.

I also looks to me that about the time that they changed sources the downward trend increased. That makes me wonder if the actual fluctuations prior to 1980 weren't really greater.

None of this means that I deny that the trend has been negative. I trust the satellite data and without question the 32 year trend is negative. 2 years of positive does not compare to 32 years but I'm not sure that 32 years is long enough either.

I didn't mention it in my earlier post but Antarctica had a lousy March. March 2010 was tied for the 7th worst March (with 1985) in the 32 year record at 4 million km. It was also down drastically from the March 2009 figure of 5 million km.

Globally March 2010 had the 3rd least sea ice in the 32 year record.

Viking12,

You know I am a skeptic but March 2010 is hardly an argument against global warming.