The world's best known advocate in the fight against climate change, former vice-president Al Gore, has endorsed democratic nominee Barack Obama after months of sitting out the primaries race and declining to pick a candidate.

Mr Gore will appear with Senator Obama at a rally in Detroit, Michigan, the capital of the car industy, in a few hours. Mr Gore won Michigan in 2000 and it is a crucial state that Senator Obama must win in November.

In an email to supporters, Mr Gore said: "Over the next four years, we are going to face many difficult challenges - including bringing our troops home from Iraq, fixing our economy, and solving the climate crisis. Barack Obama is clearly the candidate best able to solve these problems and bring change to America," Gore said.