When you survey the trail of wreckage left by the climate emails crisis, three things become clear. The first is the tendency of those who claim to be the champions of climate science to minimise their importance. Those who have most to lose if the science is wrong have perversely sought to justify the secretive and chummy ethos that some of the emails reveal. If science is not transparent and accountable, it's not science.

I believe that all supporting data, codes and programmes should be made available as soon as an article is published in a peer-reviewed journal. That anyone should have to lodge a freedom of information request to obtain them is wrong. That the request should be turned down is worse. That a scientist suggests deleting material that might be covered by that request is unjustifiable. Everyone who values the scientific process should demand complete transparency, across all branches of science.

The second observation is the tendency of those who don't give a fig about science to maximise their importance. The denial industry, which has no interest in establishing the truth about global warming, insists that these emails, which concern three or four scientists and just one or two lines of evidence, destroy the entire canon of climate science.

Even if you were to exclude every line of evidence that could possibly be disputed – the proxy records, the computer models, the complex science of clouds and ocean currents – the evidence for man-made global warming would still be unequivocal. You can see it in the measured temperature record, which goes back to 1850; in the shrinkage of glaciers and the thinning of sea ice; in the responses of wild animals and plants and the rapidly changing crop zones.

No other explanation for these shifts makes sense. Solar cycles have been out of synch with the temperature record for 40 years. The Milankovic cycle, which describes variations in the Earth's orbit, doesn't explain it either. But the warming trend is closely correlated with the accumulation of heat-trapping gases in the atmosphere. The impact of these gases can be demonstrated in the laboratory. To assert that they do not have the same effect in the atmosphere, a novel and radical theory would be required. No such theory exists. The science is not fixed – no science ever is – but it is as firm as science can be. The evidence for man-made global warming remains as strong as the evidence linking smoking to lung cancer or HIV to Aids.

The third observation is the contrast between the global scandal these emails have provoked and the muted response to 20 years of revelations about the propaganda planted by fossil fuel companies. I have placed on the Guardian's website four case studies; each of which provides a shocking example of how the denial industry works.

Two of them are drawn from Climate Cover-Up, the fascinating, funny and beautifully written new book by James Hoggan and Richard Littlemore. If every allegation it contained could not be traced back to leaked documents (I have checked all the sources), their findings would be unbelievable. Nothing exposed by the hacking of the Climatic Research Unit's server is one tenth as bad as the least of these revelations.

When I use the term denial industry, I'm referring to those who are paid to say that man-made global warming isn't happening. The great majority of people who believe this have not been paid: they have been duped. Reading Climate Cover-Up, you keep stumbling across familiar phrases and concepts which you can see every day on the comment threads. The book shows that these memes were planted by PR companies and hired experts.

The first case study I've posted reveals how a coalition of US coal companies sought to persuade people that the science is uncertain. It listed the two social groups it was trying to reach – "Target 1: Older, less educated males"; "Target 2: Younger, lower income women" – and the methods by which it would reach them. One of its findings was that "members of the public feel more confident expressing opinions on others' motivations and tactics than they do expressing opinions on scientific issues".

Remember this the next time you hear people claiming that climate scientists are only in it for the money, or that environmentalists are trying to create a communist world government: these ideas were devised and broadcast by energy companies. The people who inform me, apparently without irony, that "your article is an ad hominem attack, you four-eyed, big-nosed, commie sack of shit", or "you scaremongers will destroy the entire world economy and take us back to the Stone Age", are the unwitting recruits of campaigns they have never heard of.

The second case study reveals how Dr Patrick Michaels, one of a handful of climate change deniers with a qualification in climate science, has been lavishly paid by companies seeking to protect their profits from burning coal. As far as I can discover, none of the media outlets who use him as a commentator – including the Guardian – has disclosed this interest at the time of his appearance. Michaels is one of many people commenting on climate change who presents himself as an independent expert while being secretly paid for his services by fossil fuel companies.

The third example shows how a list published by the Heartland Institute (which has been sponsored by oil company Exxon) of 500 scientists "whose research contradicts man-made global warming scares" turns out to be nothing of the kind: as soon as these scientists found out what the institute was saying about them, many angrily demanded that their names be removed. Twenty months later, they are still on the list. The fourth example shows how, during the Bush presidency, White House officials worked with oil companies to remove regulators they didn't like and to doctor official documents about climate change.

In Climate Cover-Up, in Ross Gelbspan's books The Heat is On and Boiling Point, in my book Heat, and on the websites DeSmogBlog.com and exxonsecrets.org, you can find dozens of such examples. Together they expose a systematic, well-funded campaign to con the public. To judge by the comments you can read on this paper's website, it has worked.

But people behind these campaigns know that their claims are untrue. One of the biggest was run by the Global Climate Coalition, which represented ExxonMobil, Shell, BP, the American Petroleum Institute and several big motor manufacturers. In 1995 the coalition's own scientists reported that "the scientific basis for the greenhouse effect and the potential impact of human emissions of greenhouse gases such as CO 2 on climate is well-established and cannot be denied". The coalition hid this finding from the public, and spent millions of dollars seeking to persuade people that the opposite was true.

These people haven't fooled themselves, but they might have fooled you. Who, among those of you who claim that climate scientists are liars and environmentalists are stooges, has thought it through for yourself?