Roger Pielke, Sr. is professor emeritus of meteorology at Colorado State University and currently a senior scientist at the University of Colorado in Boulder. He has spent much of his career investigating the effects of land-use changes on the climate. Since July 2005 he has been writing a blog, Climate Science (http://climatesci.colorado.edu/), which explores many aspects of climate change. In one posting, Pielke wrote that he believes “humans are significantly altering the global climate, but in a variety of diverse ways beyond the radiative effect of carbon dioxide. The IPCC [Intergovernmental Panel on Climate Change] assessments have been too conservative in recognizing the importance of these human climate forcings, as they alter regional and global climate.” As for the Kyoto Protocol, Pielke is skeptical. “I don’t mean that carbon dioxide isn’t a problem. What I mean is that, unfortunately, it may not be our worst problem.” Pielke exchanged e-mails with ET’s managing editor Robert Bryce in early April.

ET: I don’t know who is right about the science of global climate change and whether or not anthropogenic carbon dioxide is causing global warming. Is it appropriate to think about climate change in religious terms – that is, as a division between believers and non-believers?

RP: Climate variability and change is a science issue. We need to advance our understanding by testable scientific hypotheses. It is not appropriate to let values or religion bias our performance of hypothesis testing.

ET: You’ve been a frequent critic of the IPCC and its reports. Why have so few other scientists been as willing to criticize the IPCC?

RP:There are a number who have spoken out, as illustrated by the guest weblogs on Climate Science. Most of us, however, are senior scientists who are not in a professional portion of our career where we can be intimidated. However, as I have been told directly, younger scientists have concerns that their careers will be negatively affected if they are candid in their views. Off-the-record interviews with younger scientists can be quite informative.

ET: Has there really been free and fair debate over the issue of global warming? If not, why not?

ET: In the U.K., Channel 4 recently aired a documentary that cast doubts on global warming. Is the debate in Europe on this issue freer than in the U.S.?

RP: The debate in the U.S. has been more open, particularly through the Internet, and in peer-reviewed papers and conference presentations. Some members of the European science community, however, have become more visible on this debate recently.

ET: Much of your work focuses on how land-use patterns affect climate. Why hasn’t that aspect of climate change gotten as much attention as carbon dioxide?

ET: On the day the Supreme Court ruled that the Clean Air Act covers carbon dioxide, you wrote on your blog that the “logical conclusion from this ruling is that water vapor, another emission from vehicles, can also be regulated.” How important is this ruling?

RP: The Supreme Court has opened a Pandora’s Box on what may need to be regulated, since there is a diverse variety of climate forcings besides the anthropogenic emissions of CO2. This would, based on their decision, logically include land use/land cover change.