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What is our ethical duty to eliminate carbon emissions? Was Swedish teen activist Greta Thunberg right to express such anger at the UN Climate Action Summit in New York this week?

Justin Rowlatt asks leading moral philosopher Peter Singer, professor of bioethics at Princeton University, whether someone driving a petrol- fuelled car can really be held responsible for increasing the risk of drought in Africa. And why should we give up taking long-haul flights, if the tiny amount of carbon emissions that saves will make practically no difference in the grand scheme of things?

Plus climatologist Emily Shuckburgh explains why she is not despondent about climate change - despite seeing the effects first-hand on polar research trips - and how a new institute she is heading at Cambridge University is generating a lot of excitement among academics.

Producer: Laurence Knight

(Picture: Dead cow in drought-struck Kenya; Credit: muendo/Getty Images)