It's all fine and good to denounce fossil fuels and call for the switch to renewable energy. But who's going to pay for it? Two years after the Paris Agreement, world leaders are back in the French capital for the One Planet Summit to finance that switch to renewables. So is the best approach carrot or stick? And can it all work without the United States, the world's second-biggest carbon producer? Produced by Charles WENTE, François WIBAUX and Van MEGUERDITCHIAN.