In the global warming debate, there are essentially two broad camps. One believes that the science is settled, that global warming is serious and man-made, and that urgent action must be taken to mitigate or prevent a future calamity. The other believes that the science is far from settled, that precious little is known about global warming or its likely effects, and that prudence dictates more research and caution before intervening massively in the economy.

The "science is settled" camp, much the larger of the two, includes many eminent scientists with impressive credentials. But just who are the global warming skeptics who question the studies from the great majority of climate scientists and what are their motives?

Many in the "science is settled" camp claim that the skeptics are untrustworthy -- that they are either cranks or otherwise at the periphery of their profession, or that they are in the pockets of Exxon or other corporate interests. The skeptics are increasingly being called Deniers, a term used by analogy to the Holocaust, to convey the catastrophe that could befall mankind if action is not taken. Increasingly, too, the press is taking up the Denier theme, convincing the public that the global-warming debate is over.

Many critics became involved in the global-warming debate after the publication of research by Michael Mann. You may not have heard of Mann or read Mann's study but you have often heard its famous conclusion: that the temperature increases that we have been experiencing are "likely to have been the largest of any century during the past 1,000 years" and that the "1990s was the warmest decade and 1998 the warmest year" of the millennium. You may have also heard of Mann's hockey-stick shaped graph, which showed relatively stable temperatures over most of the last millennium (the hockey stick's long handle), followed by a sharp increase (the hockey stick's blade) this century.

Mann's findings were arguably the single most influential study in swaying the public debate, and in 2001 they became the official view of the International Panel for Climate Change, the UN body that is organizing the worldwide effort to combat global warming. But Mann's work also had its critics, who published peer-reviewed critiques of their own.

Many critics found that Mann made a basic error that may be easily overlooked by someone not trained in statistical methodology, and that here was no evidence that Dr. Mann or any of the other authors in paleoclimate studies have had significant interactions with mainstream statisticians. Instead, Mann and his small group of climate scientists were working on their own, largely in isolation, and without the academic scrutiny needed to ferret out false assumptions.

Worse, the problem also applied more generally, to the broader climate-change and meteorological community, which also relied on statistical techniques in their studies. I]f statistical methods are being used, the critics argue, then statisticians ought to be funded partners engaged in the research to insure as best we possibly can that the best quality science is being done, adding that there are a host of fundamental statistical questions that beg answers in understanding climate dynamics.

In other words, the critics believe that much of the climate science that has been done should be taken with a grain of salt - although the studies may have been peer reviewed, the reviewers were often unqualified in statistics. Past studies, they believe, should be reassessed by competent statisticians and in future, the climate science world should do better at incorporating statistical know-how.

One place to start is with the American Meteorological Society, which has a committee on probability and statistics. As an example of the statistical barrenness of the climate-change world, the critics cite the American Meteorological Association's 2006 Conference on Probability and Statistics in the Atmospheric Sciences, where only eight presenters out of 62 were members of the American Statistical Association.

While the critic's advice - to use trained statisticians in studies reliant on statistics - may seem too obvious to need stating, the "science is settled" camp resists it. Mann's hockey-stick graph may be wrong, many experts now acknowledge, but they assert that he nevertheless came to the right conclusion.

To which the critics, and doubtless others who want more rigourous science, shake their heads in disbelief. They are baffled by the claim that the incorrect method doesn't matter because the answer is correct anyway. With bad science, only true believers can assert that they nevertheless obtained the right answer.