After a six-year scientific marathon that involved about 4,000 authors, contributors and reviewers and 30,000 climate studies, the U.N.'s expert panel on climate change has published its latest assessment on global warming. Now many wonder what's next.

The Intergovernmental Panel on Climate Change has answered the most important question on global warming — whether humans are causing it — with 95 percent certainty: Yes.

Next year, the IPCC is set to make a decision on its future and even the panel itself is asking whether it makes sense to embark on another mammoth climate report, which would be its sixth since 1988.

The painstaking and time-consuming work of the Nobel Peace Prize-winning group has meant that some of its findings are already out of date by the time its reports are published.

On the sidelines of the IPCC meeting in Copenhagen, The Associated Press asked climate experts inside and outside the IPCC process about the value of the panel and its giant reports. Here is what they had to say:


"There is need for a sixth report. ... There always will be areas where you need to know much more. You also need to reinforce and, may I say, re-establish what was known earlier on the basis of new research, new information. ... Therefore I would say the IPCC not only has a future, it has a very bright future."

MICHAEL OPPENHEIMER, Princeton professor and lead author of the second part of the latest IPCC assessment report:

"There are some issues with IPCC. One is this cumbersome approval process. Another is that it drains a lot of scientific time. Scientists who otherwise would be doing research. You have to ask yourself: is that the best way they should be spending their time? And the third thing is it's so long and cumbersome in its way that by the time it comes out there's a bunch of new research. ... All those are things which could be remedied if we did fewer of these comprehensive reports and more shorter, crisper or pointed interim reports."

SAM SMITH, leader of environmental group WWF's climate and energy initiative:

"I think the unique value from WWF's perspective of the IPCC is this: It represents a very conservative consensus between an enormous number of the world's best scientists and all of the world's governments. And so it provides this measuring stick which is irrefutable. You can't say 'it only represents a few scientists, or a few governments, we don't agree with it.' It's like a brick. ... If you want something that no one can deny, also at a political level, then you need something like the IPCC."

JOHN CHRISTY, climate scientist at University of Alabama, Huntsville, and former IPCC author who is skeptical of mainstream science's claim that global warming is a major problem:

"Something needs to change as these reports are biased and out-of-date by the time they are released. The system now gives almost complete control of the text to authors who have been selected by their politically-aware governments to write it and who do not reflect the enormous ignorance we still have of the climate system."

KAISA KOSONEN, climate policy adviser at Greenpeace:

"I think we need a process like this in the future as well that sort of compiles the whole story and takes the time to bring that together. ... But I do think that there would be value perhaps for the IPCC as well to do also shorter, very focused reports on certain specific issues that are advancing very fast."

CHRIS FIELD, ecologist at Carnegie Institution for Science in California and co-chair of an IPCC working group:

"The thing that I think we could do the best is not go silent over several years and then release a whole bunch of reports in one year so that the scientists are buried in work and the media doesn't know which reports to cover. ... I think that if we produce a major report every year that would be a really great outcome."

STEVE RAYNER, Oxford scientist who worked on three IPCC assessment reports but not the latest one:

"A look at the author lists over the years indicates that the working groups operate as self-perpetuating clubs. They are fairly tight networks of individuals who go on from one report to the next and cite each other's work. I decided to discontinue participation in the IPCC as it really only reports incremental changes in knowledge — nothing fundamental. Furthermore, the idea that such knowledge leads to better decision making seems quite unfounded."