Scientists and climate activists say they are under attack.
Almost 200 countries had been persuaded of the need to fight global warming with the signing of the Paris Agreement.
Now US President Donald Trump is threatening to pull the United States out of the deal, saying he is not convinced the scientists have got it right.
Marches are being held around the world to rally around the scientists and their findings on climate change.
Millions of people are also taking part in activities to mark the 50th World Earth Day.
Can people power make any difference?
Presenter: Folly Bah Thibault
Guests:
Manuel Pulgar-Vidal - head of climate and energy at the World Wildlife Fund (WWF)
Graciela Chichilnisky - a climate change economist
Dan Kanninen - former White House liaison at the Environmental Protection Agency (EPA) under the Barack Obama administration
