Remember when scientists who had cast doubt on global temperature studies boldly embarked on an effort to "reconsider" the evidence?
They have. And they conclude that their doubt was misplaced.
UC Berkeley physicist Richard Muller and others were looking at the so-called urban heat island effect - the notion that because more urban temperature stations are included in global temperature data sets than are rural ones, the global average temperature was being skewed upward because these sites tend to retain more heat. Hence, global warming trends are exaggerated.
Using data from such urban heat islands as Tokyo, they hypothesized, could introduce "a severe warming bias in global averages using urban stations."
In fact, the data trend was "opposite in sign to that expected if the urban heat island effect was adding anomalous warming to the record. The small size, and its negative sign, supports the key conclusion of prior groups that urban warming does not unduly bias estimates of recent global temperature change."
Researchers conclude that "(t)he trend analysis also supports the view that the spurious contribution of urban heating to the global average, if present, is not a strong effect; this agrees with the conclusions in the literature that we cited previously."
The literature they cite is the basis for the conclusion that Earth has been warming in an unnatural way during the period of human industrialization.
The paper, made available Thursday, amounts to the second time that Muller et al have had to back away from a key plank of climate skeptics' argument that Earth is simply on a natural temperature path and man-made greenhouse gases are not warming the atmosphere.
Several months ago, when called before a congressional panel that likewise has been skeptical of climate research, Muller acknowledged that his team was finding no smoking gun to indict climate scientists.
At the time, Muller told the House Science Committee that the work of the three principal groups that have analyzed the temperature trends underlying climate science is "excellent .... We see a global warming trend that is very similar to that previously reported by the other groups."
Explore further: Nepal to end rescue operation on trekking route