By Ed Caryl
The recent Cowtan and Way paper attempting to fill gaps in the Arctic surface temperature records by in-filling with satellite data has triggered many reactions in the blogosphere. Cowtan and Way claimed that the coverage gaps in the surface data resulted in a cooling bias that they attempted to correct with satellite derived data. Others have pointed out many failings in this paper, but have failed to note the biggest failing of all:
HUGE warming adjustment bias
The authors managed to identify a coverage bias without noting a HUGE warming adjustment bias in the surface temperatures. It is difficult to believe that they did not notice this as they were comparing the HADCRUT4 data to the satellite data. This failure totally falsifies their findings.
Here is a comparison of the GISS data for land and ocean for the region north of 60° latitude (very similar to HADCRUT4 data, but more accessible), compared to the RSS Satellite land and ocean data for the same latitudes.
Figure 1 is a plot of GISSTemp land and ocean temperatures and RSS TLT land and ocean data for latitudes north of 60°.
Others have pointed out that GISS data, and indeed all the surface temperature data bases, suffer from “homogenization” and “correction”, cooling the past and warming the present. There has been much less criticism of the satellite data because those measurements are derived in a completely different way. The surface temperature data from GISS, HADCRUT, and GHCN suffer from the same problem, a limited number of polar measurement stations (they all use the same ones). Because these stations are in very cold climates, they all suffer from varying degrees of Urban Heat Island (UHI) effects – with Arctic stations being located located near buildings, air strips, etc. The satellites suffer much less from this problem because the polar regions are so thinly populated.
Note that in Figure 1 GISSTemp is warming about 75% faster than the satellite measurements. The divergence was small in the 1980’s, mostly confined to warm years, with less difference in cold years. But in the last decade, the difference has widened to more than a degree. Figure 2 is the bias in the GISS annual temperature data relative to the satellite data.
Figure 2 is the difference between the GISS data and the RSS data in Figure 1.
So why didn’t Cowtan and Way notice this warming bias? Rhetorical question – they didn’t want to!