Professor is happy with his message of doom

H e is one of the most vilified men in the highly vilified field of climate science, yet Professor Michael Mann is jolly. Despite being the focus of a brutal campaign orchestrated by the fossil-fuel industry and the US Republican Party, Mann's cheery stoicism is positively infectious.

"I've been the focus for attack by those who deny the reality of climate change for so long that it almost seems like forever," the professor of meteorology at Pennsylvania State University says. "I'm a reluctant public figure, but have embraced the opportunity to communicate the science."

Mann became a chief target of the climate change contrarians for authoring an iconic graph of global warming science known as the "hockey stick" – the most politicised graph in science, according to the journal Nature. It was the hockey stick that generated much of the opprobrium heaped upon climate scientists as a result of the "climategate" emails stolen from the University of East Anglia and leaked on to the internet in 2010. Indeed, many of the emails were copies of correspondence between the UEA team in the UK and Mann and his colleagues in the US.

He believes the theft of the emails was not the work of a random hacker, but part of a sophisticated campaign. "It was a very successful, well-planned smear campaign intended ... to go directly at the trust the public had in scientists," he insists. "Even though they haven't solved the crime of who actually broke in, the entire apparatus for propelling this manufactured scandal on to the world stage was completely funded by the fossil-fuel front groups."

The hockey stick graph appeared to demonstrate how world temperatures had remained fairly steady for several hundred years before shooting up at the end of the 20th century, just like the straight blade jutting out from the shaft of an ice-hockey stick (the analogy doesn't quite work with a curved field hockey stick). The original study was published in Nature in 1998. Within five years, Mann had become the focus of an orchestrated campaign to undermine the entire field of climate science by rubbishing the hockey stick – a term coined by a colleague rather than Mann himself. Republican Senator Jim Inhofe picked up the hockey stick to beat climate science, famously declaring in 2003 that "global warming is the greatest hoax ever perpetrated on the American people".

Mann became the target of Freedom of Information requests and was served with a subpoena by Republican Congressman Joe Barton demanding access to his correspondence. This was followed with a subpoena from Ken Cuccinelli, the Republican Attorney General of Virginia, and yet more FOI requests from industry front-organisations, notably the American Tradition Institute.

Climate contrarians argued that Mann and his colleagues were concealing their research methods as they had something to hide. In reply, Mann insists he has been as open as he can about data and methodology, but the aim of these requests has more to do with intimidation than openness.

"What they are trying to do is blur the distinction between private correspondence and scientific data and methods, which should be out there for other scientists to attempt to reproduce," he said.

"I think it's intentional and malicious. It's intended to chill scientific discourse; to intimidate scientists working in areas that threaten these special interests.

"It's the icing on the cake if they can also get hold of any more private correspondence that they can mine and cherry pick. It's a win-win for them." Why an obscure graph published in a scientific journal should enrage so many people has been the subject of much internet conspiracy (or genuine scientific debate, depending on your point of view).

The original 1998 hockey stick study by Mann and his colleagues did, in fact, emphasise the tentative nature of estimating past temperatures before the invention of accurate thermometers. Faced with a lack of formal temperature records before the 19th century, they attempted to use "proxy records", such as ice cores, tree rings and changes to coral reefs.

Because of the nature of the approach, their graph showed large error bars, which were drawn even wider apart the further back in time they went.

Many, indeed most climate scientists have argued that the hockey-stick graph is not central to the case for the role of man-made pollution in exacerbating global warming, and the prospect of dangerous climate change. But it has nevertheless become the iconic smoking gun for both sides of the debate, showing either that we are living through unprecedented temperature increases, or that we are being duped by the biggest scientific hoax in history.

"When we first published our Nature article in 1998, we went back six centuries," Mann says.

"A year later we published a follow-up going back 1,000 years with quite a few caveats. In fact, the caveats and uncertainties appeared in the title and the abstract emphasised just how tentative this study was because of all the complicating issues.

"It's frustrating that to some extent all of that context had been lost and the result has been caricatured. Often the errors bars are stripped away, making it appear more definitive than it was ever intended."

But if the aim of the climate contrarians was to browbeat Mann and his ilk into submission, then it clearly hasn't worked.

He is publishing his own book on the hockey stick controversy later this year and he shows every sign of continuing the battle.

"Scientists have to recognise that they are in a street fight," he warns.