Former UN climate chief Christiana Figueres among signatories of letter warning that the next three years will be crucial to stopping the worst effects of global warming

Christiana Figueres, former executive secretary of the United Nations framework convention on climate change, speaks at the World Economic Forum in Davos, Switzerland, on 18 Jan 2017
Former UN climate chief Christiana Figueres: “We stand at the doorway of being able to bend the emissions curve downwards by 2020.” Photograph: Jason Alden/Getty Images