Are the climate skeptics increasingly winning the battle for public opinion? On the very eve of the Copenhagen conference, there are signs that they are — and that environmental groups are allowing them to.

Polls on both sides of the Atlantic over the last weeks indicate that fewer people now believe that global warming is taking place or that humanity is responsible. Books by prominent skeptics have become bestsellers. And in the last week a furor about e-mails hacked from a computer at Britain’s University of East Anglia have given added voice to the skeptics’ misinformation campaign that prominent scientists manipulate data to give a false impression that climate change is under way.

Perhaps the first sign of the shift came six weeks ago when a Pew Research Center poll reported “a sharp decline in the percentage of Americans who say there is solid evidence that global temperatures are rising” — only 57 percent compared to 71 percent in April 2008 and 77 percent in the two previous years. Those who believed that humans were causing it dropped to 35 percent, from 41 to 50 percent in previous polls.

Environmentalists were disturbed, but inclined to disbelieve a shift in public opinion had occurred. Possibly they were right, as far as the size of the drop was concerned. But last week a Washington Post-ABC News poll appeared to confirm the trend, suggesting that the proportion of believers had dropped from 80 to 72 percent over the past year.

Between the release of the two U.S. polls, one across the Atlantic delivered a largely similar message — only 41 percent of Britons, concluded the survey for The Times, accepted as an established scientific fact that global warming is taking place and is largely man-made.

Individual polls should, of course, be taken with a pinch of salt, as previous Grist articles have pointed out. They are influenced by how the question is put, and can be internally contradictory. Both U.S. surveys, for example, found majorities in favor of taking action to curb carbon emissions. But politicians, programmed to dismiss unfavorable findings in their public comments, still take trends very seriously. Environmentalists would be wise to do the same.

Other ominous signs are appearing. A few years ago I witnessed Lord Lawson — a former Chancellor of the Exchequer and perhaps Britain’s most prominent climate skeptic — being scorned by establishment figures when he gave a presentation on the issue. Last year, however, he published a skeptical book that sold well, and he has just launched, to a respectful reception, a think tank that will concentrate on global warming. It was an interview with him, on a breakfast radio program, that turned the East Anglian hacked e-mails affair from a blogosphere obsession to a mainstream story in Britain.

A few days ago, a call-in radio program featuring one British skeptic was so dominated by supportive calls the presenter had difficulty finding someone to stand up for climate science — something he said would have been inconceivable a year ago. Private figures suggest that some skeptic blogs that are covering the East Anglia e-mails furor are seeing huge increases in visits.

Of course, there may be many reasons for all this. The recession has certainly had an effect. And as the prospect of action to curb emissions gets closer, more people fear that they will lose out.

But environmentalists must bear a fair share of the responsibility.

Al Gore’s film An Inconvenient Truth, which took concern over global warming to its height, has also — I am sure — helped fuel the backlash. In part this is surely because he remains a politically polarizing figure, his identification with the issue helping to send Republicans in the opposite direction. But the film’s polemicism and exaggerations gave skeptics a shred of credibility when they questioned its accuracy — and effectively licensed them to engage in polemics of their own.

Environmental groups, once brilliant at swaying public opinion, have lost their touch. They have progressively become part of the establishment, while the skeptics have taken the insurgent role that environmentalists once exploited so well. As they became more and more involved in the process of formulating agreements and legislation to tackle global warming, talking to governments and attending negotiating conferences, leaders of the environmental movement have increasingly appeared to take public opinion for granted.

The East Anglia e-mail flap vividly exposes the results. From what has been publicized so far, there does not seem to be a great deal in the exposed messages, nothing that would remotely justify the widely touted claims that they prove that the whole edifice of global warming science to be a fraud. But the skeptics have had a free run with the non-scandal, while the scientists involved hunkered down (instead of touring the television studios to rebut the charges) and the green groups treated the gathering tempest as a storm in a teacup.

Climate groups appear to be following John Kerry’s example from the 2004 presidential campaign, when he initially refused to respond to the Swift Boat Veterans. Bill Clinton was wiser in his 1992 campaign, building a rapid rebuttal unit (the infamous “War Room“) to deflate charges before they could take off.

We all know — even if the greens seem to have forgotten — which candidate’s strategy was the more successful. Environmental groups would be wise to rediscover the importance of public opinion — and maybe to set up a War Room of their own.