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Here is our latest film. It tackles the most important climate issue of all - coal.

Some readers may be surprised that I rank coal at the very top of the climate agenda. I do so for a very simple reason. Unless most of the world's vast reserves of coal are kept underground then rapid climate change is, according to the scientific consensus, inevitable.

Oil and natural gas are in relatively limited supply, and will almost certainly be burnt, but there are still vast reserves of coal - nearly 1,000bn tonnes of the stuff.

The Intergovernmental Panel on Climate Change (IPCC) estimates that the CO2 stored in the world's known coal reserves would be enough to push atmospheric CO2 concentrations up to around 600 parts per million.

There is a lot of debate about what constitutes a safe level of atmospheric CO2. Pre-industrial CO2 levels were around 280ppm, now the figure is 389ppm. But virtually all scientists agree that levels above 550ppm would guarantee catastrophic climate change.

That is why US climate campaigners have made coal a key focus - just take a look at our film.

It is different here in Britain. Climate campaigners here have made the battle to block the third runway the most high profile climate issue. John Sauven, the director of Greenpeace UK, predicted the site would become "the battlefield of our generation".

In tonight's film we have an interview with the eminent Nasa climate scientist Dr James Hansen. He helped defend six campaigners charged with criminal damage after occupying the Kingsnorth coal-fired power station in Kent. He told the court the protest was justified because the 20,000 tonnes of CO2 emitted daily by the plant could lead to the extinction of 400 species. The accused were acquitted.

But when campaigners asked him to support the third runway campaign he refused. It was a major blow to the campaign. Dr Hansen said he believed the protests would not help the battle against global warming and do not deserve support.

Is Dr Hansen right? Does making aviation the focus of the climate campaign risk putting off potential supporters who don't want to change their lifestyles? Moreover, if the world's oil reserves will be burnt isn't trying to stop aviation fighting a lost cause?

That's Dr Hansen's view: "Coal is 80% of the problem," he tells us. "You have to keep your eye on the ball and not waste your efforts," he said when the Observer newspaper asked him why he would not support the Heathrow campaign. "The number one enemy is coal and we should never forget that."

Should the British environmental movement put more emphasis on coal? Is this another case of the green movement being part of the problem?