Key Points:

They believe we've bought into one of the greatest cons of all time, a gigantic fraud. Swept along by alarmist global-warming hysteria, we've been duped by a far-fetched fiction.

Their message is simple. The Earth is not warming up. Or if it is, the warming is so insignificant it's not worth bothering about. And pumping more and more carbon dioxide into the atmosphere is just fine.

They're politely referred to as climate change sceptics. In New Zealand they congregate at the website and their views are often aired on Leighton Smith's talkback radio show. For their trouble they are often mocked - as a minority of contrarians, cranks and lunatics.

Their arguments have been likened to those of the flat-earthers, the creationists or those who promote intelligent design. With the future of the planet at stake, some say their ideas are not just stupid, they're criminal. And that they should be put on trial - Nuremberg-style - as global-warming deniers.

The question many in the media are asking is whether we should pay them any attention. Do sceptical views provide balance to stories about global warming? Or are they so out of left field that giving them voice disrupts an established consensus among climate scientists that global warming is happening, and human-generated greenhouse gases are the cause. The Herald spoke to three prominent New Zealand deniers about why they think the way they do.

Wellington-based Vincent Gray describes himself as an old-fashioned scientist. The retired coal industry researcher and author of The Greenhouse Delusion got into climate-change research in the early 90s. He was enthusiastic at first but became sceptical after he had begun commenting on the Intergovernmental Panel on Climate Change (IPCC) reports. "The more I looked into it, the more suspicious I got. I've reached the stage now where I think the whole thing is almost a gigantic fraud." Like many sceptics Gray highlights the lack of total agreement and total certainty on the IPCC.

Although most scientists point to significant evidence of both global warming and the part human activity plays in its cause, there is some uncertainty about the size of that role. There's debate too about just how much effect global warming will have on the planet. Asked where he sits on the uncertainty continuum, he interrupts the question. "No, no, I don't agree at all. There is no uncertainty - it's a complex thing. The claim is, of course, that there has been an increase in temperature. This claim, in my opinion, is false."

Gray is well aware of the mocking and the name-calling views like his attract. "Oh yes, I expect to have my tyres slashed. It's like a religious belief. It's a form of fanaticism." He describes what's driving the global-warming lobby as the secular religion of environmentalism. "Somehow people wish to believe the Earth is being destroyed by humans."

As for being called a denier - a pejorative intended to compare the anti-global warming arguments with those used in Holocaust denial - Gray says it's the environmentalists who are committing crimes against humanity, just as they did when they stopped the use of DDT in the fight against malaria.

"It's much the same with global warming. They will stop us from keeping warm or from developing our cities. Or from saving money. Poor people will continue to starve and so on. The measures that are being taken are actually harmful to people."

Gray finds it difficult to get his views aired, which he's why he's unashamed about being published by the Tech Central Science Foundation - an organisation that has received US$95,000 ($141,000) in funding from ExxonMobil. He says he hasn't received any funding from fossil fuel industries. His most recent paper was published in the climate sceptic journal Energy and Environment.

"The reason it's published there is because nobody would publish it in one of the so called peer-reviewed journals, which are a little closed circle who won't allow people who disagree with them to publish. The editors of Nature and Science are both raving global warmers."

Former chief meteorologist and TV weather presenter Augie Auer was drawn into the climate change debate when the Government started proposing taxes. "They drew the line in the sand for Augie Auer when this suddenly became a punitive measure - 'we're going to be taxed for this, we're going to have to pay.' I thought this is ridiculous."

The past professor of atmospheric science at the University of Wyoming believes the global-warming lobby is based on bad science and that the computer projections used are off beam. "I'm a firm believer that good science always prevails. I'm a patient man. This issue will be settled once and for all come 2030 or 2050 when we'll say, 'Gee we're still here'. Then people will look back and laugh."

Auer is not impressed with former United States Vice-President Al Gore's view that global warming is no longer just an issue of science, but one of morality - redefined as a choice between good and evil. "I would agree with him there is an issue of morality except he's the one that is a bit immoral about conning everyone with this particular thing."

Auer says he's seen this sort of hysteria before - in the debate about the effect of fluorocarbons on the ozone hole, and about nuclear power. He says much of the current climate change can be explained by natural cycles and there may be other explanations such as solar activity. "People think I don't care about pollution - sure I do. I don't want things all garbled up, but I also understand the physics of the atmosphere and I know how she works." Against the prevailing wisdom he argues it "won't make a hill of beans difference" if we double the amount of carbon dioxide in the atmosphere. "I have but one wish and that is to live long enough to prove the bastards wrong."

AMONG global warming sceptics Chris de Freitas is our uber denier. The associate professor at the University of Auckland's School of Geography and Environmental Science is published far and wide arguing against global warming. He is a frequent dissenting voice in the media and ranks alongside big-name deniers such as Denmark's Bjorn Lomberg, and the United States' Ross McKitrick and Fred Singer.

His stance has seen him described as a "toxic sceptic" - a title that doesn't bother him. "I'm attacked all the time internationally. I'm attacked in the US Senate ... I personally don't lose any sleep over it."

But what de Freitas finds really incredible is that so many are listening to Al Gore and not to people like him. "I don't see how a politician, especially a failed presidential politician, should be seen as an authority on a scientific matter." He says Gore's movie An Inconvenient Truth epitomises all that is wrong with the global-warming debate - that it's highly politicised, biased, selective and emotional.

De Freitas, on the other hand, paints himself as coldly detached, analytical and sceptical - as any good scientist should be. "It might be an inconvenient truth, but it's not inconvenient for me not to believe it. I spend a lot of my time disbelieving things."

In de Freitas' judgment, the case for global warming doesn't stack up. His conversation is peppered with phrases of denial: "that is not correct at all ... that is absurd ... that was debunked as being silly ... not a single scientist has come close to answering that question ... there is no robust evidence ... " Sometimes he's less than scholarly: " ... well, in fact the polar bear population is in good health - I'm not a polar bear expert ... " Sometimes he goes into bat for the other side: "I'm not saying it's [global warming] not caused by human action. It would be silly to say that since I have no evidence that it isn't."

But mostly he stays staunchly and volubly on message: " ... not one shred of evidence ... was shown to be a scam ... it verges on being fiction ... "

As for being called a denier, about undermining and delaying precautionary efforts governments might be taking, de Freitas is unrepentant and turns the accusation around. "What happens if it's all shown to be a hoax? Who is liable then? These people are responsible. They are making claims, worrying others, based on shonky science ... they should be held liable for the costly and very serious misleading information they are giving."

De Freitas says the global warming lobby has many agenda - the main one being that the academic and science community is sloshing in climate change research money. "It makes sense to hitch your horse to that wagon because you're likely to get funding."

He does acknowledge, however, that he gets something from the multi-billion dollar global warming business too. "My reputation internationally is probably based on scepticism. In a sense I could say I'm part of the global warming industry, but that sort of thing is irrelevant. It's the science that matters."

What annoys de Freitas most is any suggestion he represents a minority view. "But is it a minority position? How do you know that?" Point out the consensus statements made by the climate change panel or by the academies of science in countries all over the world, and he changes tack. "They [the IPCC] said there was a consensus of opinion. They issued that to cut out any debate - so if you weren't with the consensus you were incredible. That's very unscientific. "

He gets annoyed, too, when people refuse to engage with him, but sees it as a further sign he's right. "People like Pete Hodgson when he was climate change minister would avoid being in the same room as me. People who challenge me are scared of facing me in a debate."

Does he feel marginalised at Auckland University? "The Vice-Chancellor might get the odd letter saying I'm a disgrace to the university, but he's used to that because it happens in other areas too." And by his colleagues? "My colleagues are actually quite civil to me. I don't know what goes through their heads. They have a different view to me - that's fine."

So would he fail students who represent IPCC views? "Oh no, you fail students who don't think for themselves ... I encourage them to believe what they want to believe based on their critical assessment." They do challenge him on the boundaries between critical and contrarian views. "My students often ask me, if I get it, how come so many others don't?" Staunch as ever, de Freitas diverts the question, saying science is not about opinion polling.