Historians of science would be surprised if there weren't people unwilling to concede that global warming is caused by human activity no matter how much evidence accumulates to the contrary:
Global Warming -- Signed, Sealed and Delivered, by Naomi Oreskes, Commentary, LA Times: An Op-Ed article in the Wall Street Journal a month ago claimed that a published study affirming the existence of a scientific consensus on the reality of global warming had been refuted. This charge was repeated again last week, in a hearing of the House Committee on Energy and Commerce.
I am the author of that study, which appeared two years ago in the journal Science, and I'm here to tell you that the consensus stands. The argument put forward in the Wall Street Journal was based on an Internet posting; it has not appeared in a peer-reviewed journal — the normal way to challenge an academic finding. (The Wall Street Journal didn't even get my name right!)
My study demonstrated that there is no significant disagreement within the scientific community that the Earth is warming and that human activities are the principal cause. .... Not a single paper in a large sample of peer-reviewed scientific journals between 1993 and 2003 refuted the consensus position...
To be sure, there are a handful of scientists, including MIT professor Richard Lindzen, the author of the Wall Street Journal editorial, who disagree with the rest of the scientific community. To a historian of science like me, this is not surprising. In any scientific community, there are always some individuals who simply refuse to accept new ideas and evidence. This is especially true when the new evidence strikes at their core beliefs and values.
Earth scientists long believed that humans were insignificant in comparison with the vastness of geological time and the power of geophysical forces. For this reason, many were reluctant to accept that humans had become a force of nature, and it took decades for the present understanding to be achieved. Those few who refuse to accept it are not ignorant, but they are stubborn. They are not unintelligent, but they are stuck on details that cloud the larger issue. Scientific communities include tortoises and hares, mavericks and mules.
A historical example will help... In the 1920s, the distinguished Cambridge geophysicist Harold Jeffreys rejected the idea of continental drift on the grounds of physical impossibility. In the 1950s, geologists and geophysicists began to accumulate overwhelming evidence of the reality of continental motion... By the late 1960s, the theory of plate tectonics was on the road to near-universal acceptance.
Yet Jeffreys, by then Sir Harold, stubbornly refused to accept the new evidence, repeating his old arguments about the impossibility of the thing. He was a great man, but he had become a scientific mule. For a while, journals continued to publish Jeffreys' arguments, but after a while he had nothing new to say. He died denying plate tectonics. The scientific debate was over.
So it is with climate change today. As American geologist Harry Hess said in the 1960s about plate tectonics, one can quibble about the details, but the overall picture is clear.
Yet some climate-change deniers insist that the observed changes might be natural, perhaps caused by variations in solar irradiance or other forces we don't yet understand. Perhaps there are other explanations for the receding glaciers. But "perhaps" is not evidence. ... Climate-change deniers can imagine all the hypotheses they like, but it will not change the facts...
None of this is to say that there are no uncertainties left — there are always uncertainties in any live science. Agreeing about the reality and causes of current global warming is not the same as agreeing about what will happen in the future. There is continuing debate in the scientific community over the likely rate of future change: not "whether" but "how much" and "how soon." And this is precisely why we need to act today: because the longer we wait, the worse the problem will become, and the harder it will be to solve.