Over the years, Muller has praised Watts' efforts to show that weather station data in official studies are untrustworthy because of the urban heat island effect, which boosts temperature readings in areas that have been encroached on by cities and suburbs.
But leading climatologists said the previous studies accounted for the effect, and the Berkeley analysis is confirming that, Muller acknowledged. "Did such poor station quality exaggerate the estimates of global warming?" he asked in his written testimony. "We've studied this issue, and our preliminary answer is no."