In addition to the excellent Pajamas Media interview, I recommend the also well done interview by Andy Revkin titled Critic of ‘Climate Oligarchy’ Defends Case for CO2-Driven Warming at Dot Earth [although the more complete and accurate title would be “Critic of ‘Climate Oligarchy’ Defends Case For Human Driven Climate Change”].
My answer to Andy’s questions start with
“The C.R.U. is only one of several groups who are analyzing the long term global average surface temperature trends drawing from mostly the same raw observed data. Even if their data analysis is excluded, it does not alter the findings that were reported in the 2007 I.P.C.C. report with respect to the surface temperature trends, since these other analyses provide a redundant check of their analyses over the last century. Over the last 100 years or so this surface data clearly documents a long-term warming.
There are remaining problems with the quantitative accuracy of these surface temperature data sets, however, as we have presented in several multi-authored recent papers. For example, most recently in Klotzbach et al 2009, we find a significant divergence between the lower tropospheric and surface temperature trends, which can be explained in part by the more limited vertical sampling of temperature trends using just the surface temperature data. This indicates that the long-term surface temperature trends overstate the warming relative to warming through a deeper depth of the troposphere.
In any case, the surface temperature trends are not the most appropriate metric to assess global warming (or cooling) as it is the oceans, which are the largest component of heat changes, as I discussed most recently in my Physics Today paper. This is an issue that I agree with Jim Hansen on. Since mid-2003 through the latest data that I have seen, there has been no annual average warming or cooling in the upper oceans. I recommend you contact Josh Willis for the latest information. For future assessments, this should be the metric to use to monitor (and seek to predict) global warming.
There is also a question of attribution. First, it needs to be better recognized that global warming (i.e., climate system heat changes) is only a subset of climate change. Humans are altering the climate in diverse ways, a variety of human climate forcings are significant, and the effects of these forcings need to be responded to, even if the climate did not warm.”
See the full interview for the rest of my comments.