Nasa scientist appears in court to fan the flames of coal power station row

The Nasa scientist who first drew attention to global warming 20 years ago appeared in a British court yesterday as a key witness in support of climate change activists charged with damaging a power station.

Professor James Hansen gave evidence at Maidstone Crown Court in the case of six Greenpeace members who scaled a 630ft chimney at the Kingsnorth plant in Hoo, Kent, last October in protest against plans to build new coal-fired units there.

The activists planned to paint the slogan "Gordon Bin It" on the chimney, but only got as far as the Prime Minister's christian name before they obeyed a High Court injunction ordering them down. They were charged with causing £35,000 of damage – the sum it cost the plant's owner, E.ON, to scrub off the word "Gordon".

Greenpeace argues that under the Criminal Damage Act 1971, its activists had a "lawful excuse" to cause the damage because they were seeking to prevent even greater damage being caused to property – such as flooding from rising sea levels and damage to species caused by climate change.

Yesterday, Prof Hansen, who has spoken out against the Bush administration's stance on global warming, said Britain had a responsibility to take a lead on limiting climate change because it was responsible – owing to its long industrial past – for much of the CO2 already in the atmosphere. Phasing out coal-burning power stations was crucial in tackling global warming, he told the court.

"Somebody needs to stand up and take a leadership role," Prof Hansen said. "It is an opportunity for the Prime Minister. If we are to avoid disintegration of the ice sheets, minimise species extiction and halt or reverse... climate change there is just time to accomplish it, but it requires an immediate moratorium on new coal-fired power plants that do not capture or sequester CO2."

Prof Hansen joined the Kingsnorth debate in December when he wrote to Gordon Brown and urged him to drop plans for coal-fired plants that do not capture CO2 emissions. E.ON wants to build two new coal-fired units at the ageing plant. The Government is considering whether to approve the planning application.

Before travelling to Kent, Prof Hansen met the David Miliband, the Foreign Secretary, who is thought to be unhappy about the plan for Kingsnorth, which is being promoted by John Hutton, the Business Secretary. Mr Brown will have the final say later this year.