Last year Anthony Watts said that it was a certainty that siting differences caused a warm bias:
“I can say with certainty that our findings show that there are differences in siting that cause a difference in temperatures, not only from a high and low type measurement but also from a trend measurement and a trend calculation.”
“The early arguments against this project said that all of these different biases are going to cancel themselves out and there would be cool biases as well as warm biases, but we discovered that that wasn’t the case. The vast majority of them are warm biases, and even such things as people thinking a tree might in fact keep the temperature cooler doesn’t really end up that way.”
Temperature trend estimates vary according to site classification, with poor siting leading to an overestimate of minimum temperature trends and an underestimate of maximum temperature trends, resulting in particular in a substantial difference in estimates of the diurnal temperature range trends. The opposite-signed differences of maximum and minimum temperature trends are similar in magnitude, so that the overall mean temperature trends are nearly identical across site classifications.
After spending so much time claiming that the data collected in the US was inaccurate and should not be used in discussing AGW, their peer-reviewed paper shows the opposite.
There may be problems with individual sites but it appears that the law of large numbers overcomes these. In fact it does not matter if only the best sites are used in the data analysis or not. The results are the same.
And they show that both day and night temperatures are rising at the same rate. This suggests that the sun itself is not totally responsible. If t was, nighttime temperatures – with no sun – should have a different trendline than daytime temperatures. The same thing must be affecting both temperatures, making increasing carbon dioxide levels the most likely culprit.
So, the scientists that have been disparaged by many of these denialists were actually right.