Read here. Willis Eschenbach at WUWT provides a great explanation of how NASA managed to find a huge warming in the Arctic during the incredibly cold 2009-2010 winter for the Northern Hemisphere. (We mentioned this curiosity in a previous post.) It appears the NASA method of fabricating temperatures for the Arctic is so incredibly stupid, no other climate group will utilize the method nor vouch for how NASA does it.
"My understanding is that the biggest source of this discrepancy [between global temperature datasets] is the way the Arctic is analyzed. We know that the sea ice was at record low values, 22% lower than the previous low in 2005. Some sea temperatures and air temperatures were as much as 7C above normal. But most places there is no conventional data. In NASA [GISTEMP] they extrapolate and build in the high temperatures in the Arctic. In the other records [CRU, NCDC, or USHCN] they do not. They use only the data available and the rest is missing."Back in the 70's, this type of idiocy would be referred to as the 'Peter Principle' in action.