I have been certain for a long time that the temperature record used by the AGW supporters was manipulated to show a significant temperature increase. Data presented in the Appendix to Michael Crichton's book State of Fear clearly showed that there had been little or no temperature increase during the 20th century. Data from Central England shows that the rate of temperature increase there has been the same for the last 300 years. The fact that those compiling the data refused to reveal how the manipulated the data cast suspicion of objective people on the results. As far as I know there has been no paper presented that shows that the data manipulation methods were valid. And, to me Phil Jones' paper that purported to show that the urban heat island effect was insignificant was suspect because he would not share the raw data used, and later claimed hat the data were lost (the classic "dog ate my homework" excuse). Here is a paper that looks at the data manipulation done by NCDC in the US.