MIT atmospheric chemist Ronald Prinn, a lead author of the latest international climate change assessment, talks about the struggle to find consensus among so many scientists.

Jennifer Weeks

Since its creation in 1988, the Intergovernmental Panel on Climate Change (IPCC) has carried out four assessments of climate change science, impacts, and mitigation options. The release earlier this month of the summary for policymakers about the science of climate change will be followed by reports on impacts, mitigation, and a synthesis report later this year.

IPCC reports are unique in science in that they are written based on consensus from several hundreds of scientists, representing a broad cross-section of opinion from many nations and disciplines. In the days leading up to the release of the report, news articles were reporting the late night sessions and debates as scientists worked to finalize the wording.

MIT atmospheric scientist Ronald Prinn has contributed to all four assessments and served as one of the lead authors of last week’s report. He focused on the section describing the sources and changes in concentrations of greenhouse gases. Prinn spoke with NNB about his experiences getting so many scientists to agree on a single document.

What’s it like being a lead author?

There’s a lot of discussion and exchange with scientists around the world, first to make sure that we have all the latest data, then looking at the literature to see what people think are the causes for what we’re seeing. You have to assess all of the work out there and try to come to some conclusions that represent the state of knowledge. Lead authors lay the foundation for what goes into the report–each one brings his or her brick to the project. It’s very time-consuming, and you don’t get excused from your existing work–scientists who participate in IPCC assessments do it in their spare time.

Were there a lot of disagreements or heated debates?

We didn’t have problems working together, but we had some difficult issues to resolve. There’s been a lot of debate recently about how greenhouse gases like methane are removed from the atmosphere. That process is very complex and is driven by things that people think of mostly as local and urban air pollution, but which are folded into the climate system because they affect the ability of the atmosphere to cleanse itself. This area has generated a lot of intense discussion for four or five years that we had to resolve, but papers coming out right as we were doing the assessment helped us form some definite conclusions.

Back in 2001 you coauthored a Science article that pointed out what you saw as flaws in the third IPCC report. What were your main concerns?

We were concerned that the Third Assessment Report did not take a good scientific approach to defining uncertainties for all of the key numbers that were important for society to make a decision. We made a strong point that every future assessment should have an uncertainty range attached. To make economic and policy decisions, you need some sense of how likely it is that a range of temperatures will occur.

Does the new study address uncertainty more clearly?

Yes, and I’m delighted that the leadership took that approach–it states the likelihood that changes will lie within specific ranges, as best as we can project right now. The numbers and ranges in this report will be debated, and they will be refined in the next assessment, but that’s much better than having no ranges attached to the estimates. It’s a very big step forward.

Has your view of the IPCC changed after serving as a lead author?

I think the process has improved from 2001. In addition to the uncertainty issues, the review process has some new elements. When we sought comments on the draft report, we got thousands of responses back and we had to answer every one carefully in writing. Then some authors who were not involved in writing the main study acted as review editors: they looked at how we answered outside comments and had the power to remove text or have it revised. There is also much more extensive documentation of the review process.