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This month activists all over the world have taken over city centres, demanding urgent action to halt climate change. They say we need to eliminate all carbon emissions by 2025. Most people think that’s impossible. But scientists are warning that if we want to stop global warming, we need to cut our CO2 emissions fast. So how soon can the planet achieve carbon zero?

Helen Grady speaks to:

Chukwumerije Okereke, professor in Environment and Development at Department of Geography and Environmental Science, University of Reading and director of the Centre for Climate Change and Development, Alex Ekwueme Federal University (AE-FUNAI), Ndufu-Alike, Ebonyi state, Nigeria; Mercedes Maroto-Valer, Director of the Research Centre for Carbon Solutions at Herriot Watt University in Edinburgh, Scotland; Roger Pielke Junior, Professor at the University of Colorado; Rachel Moncrief, deputy director at the International Council on Clean Transportation

Producer: Beth Sagar-Fenton

(Photo: Wind turbines in California USA. Credit: David McNew/Getty Images)