An estimated 40,000 people hit London streets on Sunday, joining hundreds of thousands in New York calling for worldwide action on climate change.
The global coordinated action of more than 2,000 events comes ahead of the United Nations climate change meeting in New York on Tuesday.
Oscar-winning actress Emma Thompson was there rubbing shoulders with protestors.
And the Greenpeace Ambassador also addressed the crowd, especially critical of the environmental policies of UK Prime Minister David Cameron.
She was joined by singer-songwriter Peter Gabriel and fashion designer Vivienne Westwood.
Nestled in the crowd taking selfies was a face-painted Russell Brand.
A lot of people on the #climatemarch were eccentric.
Who was understandably a hit with the crowd.
Greenpeace. Silverface. From today's #ClimateMarch
