An article in the New York Times by John Tierney reports on the discrepancy between various measurements to the Global Mean Temperature in 2007 from four credible scientific groups.
The NASA GISS surface temperature measurement is nearly 0.15° C higher than that measured by RCC. The discrepancy with the satellite measurements is even higher. While the debate rages over whose measurement is more accurate today, they conveniently overlook the elephant-in-the-room, namely that Climatologists claim similar accuracy in estimating the Global Mean Temperature in the year 1880 based on much more limited data collected with much more primitive instruments!
As always, Garbage IN = Garbage OUT.