I have referred to it before, but since I have been posting today on surface temperature measurement, I thought I would share a bit more on "Quantifying the influence of anthropogenic surface processes and inhomogeneities on gridded global climate data" by Patrick Michaels and Ross McKitrick that was published two weeks ago in Journal of Geophysical Research – Atmospheres (via the Reference Frame).
Michaels and McKitrick found what nearly every sane observer of surface temperature measurement has known for years: That surface temperature readings are biased by urban growth. The temperature measurement station I documented in Tucson has been reading for 100 years or so. A century ago, it was out alone in the desert in a one horse town. Today, it is in the middle of an asphalt parking lot dead center of a town of over 500,000 people.
Here is what they did and found:
They start with the following thesis. If the temperature data really measure the climate and its warming and if we assume that the warming has a global character, these data as a function of the station should be uncorrelated to various socioeconomic variables such as the GDP, its growth, literacy, population growth, and the trend of coal consumption. For example, the IPCC claims that less than 10% of the warming trend over land was due to urbanization.
However, Michaels and McKitrick do something with the null hypothesis that there is no correlation – something that should normally be done with all hypotheses: to test it. The probability that this hypothesis is correct turns out to be smaller than 10-13. Virtually every socioeconomic influence seems to be correlated with the temperature trend. Once these effects are subtracted, they argue that the surface warming over land in the last 25 years or so was about 50% of the value that can be uncritically extracted from the weather stations.
Moreover, as a consistency check, after they subtract the effects now attributed to socioeconomic factors, the data from the weather stations become much more compatible with the satellite data! The first author thinks that it is the most interesting aspect of their present paper and I understand where he is coming from.
What they are referring to in this last paragraph is the fact that satellites have been showing a temperature anomaly in the troposphere about half the size of the surface temperature readings, despite the fact that the theory of global warming says pretty clearly that the troposphere should warm from CO2 more than the surface.
I will repeat what I said before: The ONLY reason I can think of that climate scientists still eschew satellite measurement in favor of surface temperature measurement is because the surface readings are higher. Relying on the likely more accurate satellite data would only increase the already substantial divergence problem they have between their models and reality.