Several weeks ago, NASA was forced to restate downwards recent US temperature numbers due to an error found by Steve McIntyre (and friends). The restatement reinforced the finding that the US really has not had much warming over the last 100 years. James Hansen, emporer of the NASA data for whom the rest of us are just "court jesters" dismissed both the restatement and the lack of warming trend in the US as irrelevent because the US only makes up about 2% of the world’s surface.
This is a fairly facile statement, and Hansen has to know it. Three quarters of the earth’s surface is water for which we have no real long term temperature record of any quality. Large masses like Antarctica, South America, and Africa have very few places where temperature has been measured for any long period of time. In fact, via Anthony Watts, here is the world map of temperature measurement points that have data for all of the 20th century (of whatever quality):
So the US is irrelevent, is it? There is some danger in trying to eyeball such things, but I would say that the US is about one-half to one-third of the world’s landmass that has continuous temperature coverage. I won’t get into this today, but for all the quality issues that have been identified in US measurements (particularly upwards urban biases) these problems are much greater in the rest of the world.
Further to Hansen’s point that the US does not matter, here is a quote from Hansen last week (emphasis added)
Another favorite target of those who would raise doubt about the reality of global warming is the lack of quality data from South America and Africa, a legitimate concern. You will note in our maps of temperature change some blotches in South America and Africa, which are probably due to bad data. Our procedure does not throw out data because it looks unrealistic, as that would be subjective. But what is the global significance of these regions of exceptionally poor data? As shown by Figure 1, omission of South America and Africa has only a tiny effect on the global temperature change. Indeed, the difference that omitting these areas makes is to increase the global temperature change by (an entirely insignificant) 0.01C.
Look at the map! He is now saying that the US, South America, and Africa are irrelevent to world temperatures. And with little ocean coverage and almost no coverage in Antarctica before 1960, what are we left with? What does matter? How is he weighting his temperature aggregations if none of these matter? Fortunately, the code is finally in the open, so we may find out.