Tens of thousands of people - including some A-list celebrities - have mobilised around the world in marches calling for action on climate change.

The People's Climate Marches come ahead of a UN summit on the issue tomorrow.

Oscar winning actress Emma Thompson has taken part in the London rally and says now is the time for change.

"The science is all there.

"Anyone now who tries to deny it not looks a little bit bonkers.

"So now we have the science, we have to recognise the fact, I am sorry to have to say that our economy is going to have to change."