The East Anglia emails were released just weeks before world leaders gathered in Copenhagen in December to continue talks on a new treaty to curb greenhouse gas emissions. Many saw this as a deliberate attempt to undermine the summit, which produced a disappointing outcome.
Today, the third and final review of the emails affair cleared the scientists involved of any dishonesty over data. But while the Muir Russell report may have exonerated the "rigour and honesty" of the scientists and the science, did the fuss over the emails contribute to the failure at Copenhagen to agree a meaningful deal? Was there a swing in public opinion that saw politicians retreat from the previously bullish positions on climate?
Ben Stewart, head of media at Greenpeace, says the emails controversy had a significant impact. "It's pretty hard to say what the impact has been but it would be hopelessly naive to say it has not had an effect. To peak and decline our emissions was always going to need us to push a large rock up a steep hill, but the rock got heavier and the hill got steeper because of the reporting of the emails."
Stewart says it is the media, not the CRU scientists, who are to blame for any extra confusion among the public. "The public haven't read a thousand emails from scientists they have never heard of. The emails didn't change the way that carbon dioxide traps heat in the atmosphere, but the media created a situation that presented a false symmetry between the various sides of the debate."
Michael Jacobs, former special adviser on climate to Gordon Brown, and a figure central to the way the climate debate has unfolded in the UK, says: "I don't think it [the release of the emails] had an impact on Copenhagen. It affected the mood but not the outcome. The emails gave a huge boost to the sceptics but we didn't see a weakening of commitments on climate at a state level anywhere. Any government that wanted to stall action could have played up the importance of the emails and called for more enquiries, but that didn't happen, so I think they had less of an impact than some people were claiming."
Saudi Arabia, long-standing opponents of a global agreements to curb emissions, tried to use the emails controversy to bolster their position in Copenhagen. China cited them once, but made little headway.
Jacobs, now a research fellow at the London School of Economics, adds: "Since Copenhagen it's very difficult to tell. There's no question that climate agnosticism has increased, but I think that has more to do with a backlash to all the hype around Copenhagen. We were worried about the impact [of the emails] on public opinion but government action on climate change is not driven by public attitudes, but that it is the right thing to do. Public consent is important but not essential so long as there is not downright opposition. Governments introduce plenty of things that are less popular than action on climate."
Bob Ward, policy and communications director at the Grantham Research Institute on Climate Change and the Environment, said: "It hasn't in any direct way affected the political process. Governments have scientific advisers who know this is just a storm in a teacup."
There could be an indirect effect, he said, from a confused public who feel there is less need to pressure politicians to cut emissions. "But I haven't seen any evidence there has been any big change in public opinion."
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