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.