ustin Rowlatt looks at the monumental challenge of weaning ourselves off fossil fuels. Solar and wind could meet all of humanity’s energy needs, but can we switch over before climate disaster strikes?

According to clean-tech enthusiast and investor Ramez Naam, we have the means at our disposal. Our fossil-fuelled global economy has enabled a rapid collapse in the cost of renewable energy and electric vehicles. And now we are seeing a snowballing of government action to decarbonise our economies, according to UN climate negotiator Christiana Figueres. But many problems remain. Energy historian Vaclav Smil points out that we still have no easy way to store renewable energy, or use it to make billions of tonnes of cement and steel. Sheffield-based ITM Power hope that their green hydrogen could solve many of these problems. Plus, electricity historian Julie Cohn says another option might be to build a global electricity grid.