As politicians and statesmen soon head off to Copenhagen to renew their governments' political commitments to reduce carbon emissions, we should all remember there are two separate hypotheses driving the movement: first, that the world's climate is warming, and second, that this warming is at least partly caused by man's activities - specifically, by the injection of millions of tons of carbon into the atmosphere each year, largely through the burning of fossil fuels. These two hypotheses together form the foundation for the theory of man-caused, or anthropogenic, global warming ("AGW"). Both these hypotheses are probably true, but the extent to which they are is not really known. Our world was in a warming period before the Industrial Age began, for instance, and a lot of the recently observed increases in temperatures might just be natural. On the other hand, with a system as complex and feedback-driven as the world's climate, big changes might come suddenly, in a kind of phase transition, with little actual advance warning or observable trend. As a species, we should want all our best scientific brains investigating this danger to better understand it, without fear of reprisal.

These days, nearly every media report on global warming specifies that the science behind it is "universally accepted" and "beyond dispute," but this is not true. The theory of AGW is not like the theory of relativity, or even the theory of evolution, both of which are well understood, and have been observed, demonstrated and confirmed again and again, in thousands of experiments and research studies. The climate is an extraordinarily difficult system to understand, even with sophisticated computer models. Systemic "experiments" that prove or disprove various elements of the AGW theory are nearly impossible to conduct. Just 30 years ago, in fact, the greatest scientific fear about our climate was that the world was cooling and might soon experience a new ice age. The Earth has warmed and cooled significantly in the past, way before man's use of fossil fuels, but calculating the magnitude and effects of these past climate changes by analyzing tree rings or taking core samples from ice sheets is not foolproof, nor do we really understand what causes many of these cycles.

However, if AGW really is true, then only drastic, costly governmental intervention will ensure that carbon emissions can be reduced enough to have any real impact, and many critics point out that even the most draconian government measures proposed to date are simply unlikely to succeed, despite their disastrously high costs. The funds required to reduce carbon emissions could be used, alternatively, to completely eradicate malaria, or wipe out AIDS, or both. There may be technological solutions that don't have as high a cost (carbon absorption sinks, nanotechnology, genetically engineered carbon-eating organisms, and so forth). Moreover, the actual consequences of a warmer world are not universally bad. Fewer people die from heat than die from cold every year. A warmer climate mostly means milder winters, rather than hotter summers. Agriculture will become more difficult in some regions but is likely to be much more productive in many more regions. And the apocalyptic idea that global warming will cause sea levels to rise by as much as 40 feet (see Al Gore's An Inconvenient Truth) was always nonsensical; even the most vocal AGW boosters are now careful to distance themselves from such scare-mongering.

In short, there is still a great deal more we need to learn about AGW, and if the consequences are as imminent and damaging as many reports say, then we need to learn about it all the more quickly. It is therefore a gross disservice to humanity for scientists on either side of the AGW investigation to try to rig the debate.

This "climate-gate" scandal has ignited a firestorm of I-told-you-so protest from the conservative media, including Wall Street Journal editorial writers and Fox News. Some scientists brand this criticism of the AGW movement from the right side of the political spectrum as non-scientific, and they are right, because most of the criticism is based on politics and economics, not science. But if AGW necessitates severe government intervention, then we really can't entirely separate the science from the politics. These more conservative media voices have no special claim to scientific expertise, but they do tend to give greater weight to the serious costs and reduced personal liberties likely to result from most of the solutions proposed by the AGW crowd. What we need from scientists is the most objective, balanced evaluation of the problem that we can plausibly obtain, and it turns out that this is not what the Climate Research Unit was giving us. It was building a stronger case than would be justified, based on what turns out to be a false consensus.

Still, it's not hard to empathize with the climate scientists involved. After all, if you have a strongly held belief that man's activities are threatening the world's climate, and that if something isn't done soon then we will all suffer severe consequences - well, obviously you will do what you can to make sure this doesn't happen. And you'll want to make the argument as strong as you can make it, in order to mobilize action. But these scientists have no more political expertise or authority than the Wall Street Journal has scientific authority.

When I read media statements that man-made global warming is "beyond dispute" I cringe. It reminds me of other great examples of global consensus, including even the most recent financial crisis, driven by the universal conviction that housing prices would continue to rise, no matter what. Or consider the run-up to the invasion of Iraq, when it was agreed by virtually all the Western World's intelligence services that Saddam Hussein was in fact harboring weapons of mass destruction. This was not a lie being told to the public by intelligence agencies, any more than global warming is a lie being perpetrated on the UN by scientists. There was a sincere, rational belief, based on a lot of evidence, that Iraq had WMDs. No one had actually put their hands on one of these WMDs, but none of the intelligence services doubted that Iraq actually had them or would soon have them - not the French, not the British, not the Germans, not even the Russians. And in view of the consequences involved, the political officials who felt most strongly about the issue bent over backwards to make their case as persuasively as possible in front of the world public. Who could forget Colin Powell's detailed and damning address to the UN?

Those of you who follow my blog posts know that I, personally, am a big skeptic when it comes to AGW, as are many reputable scientists, but this is not what I'm writing about here. I think the climate scientists whose emails were stolen do have a point. There is good evidence that the world's climate is heating up, and that man is at least partly responsible. However, there is also a lot more room for doubt than most people appreciate - certainly more than most reporters apparently understand.

Life is complex, and issues like global warming are difficult to analyze, so we need to be tolerant of dissenting opinions. Dissent, when properly handled, makes our decisions more intelligent. We won't get smarter, as a species, if we don't tolerate - indeed welcome - a variety of points of view. And, in the same way that the East Anglia scientists should welcome dissenting views on their own theories, the anti-AGW crowd also needs to calm down a bit and realize that just because private emails reveal that climate scientists "fight the hard fight," it doesn't necessarily mean that the science behind AGW isn't legitimate. Colin Powell presented a highly persuasive case for WMD that, it turned out, were never found in Iraq. But that doesn't mean he wasn't sincere in his belief, and motivated by an urge to do the right thing.