Cooling the planet by filtering excess carbon dioxide out of the air on an industrial scale would require a new, massive global industry – what would it need to work?

The year is 2050. Walk out of the Permian Basin Petroleum Museum in Midland, Texas, and drive north across the sun-baked scrub where a few remaining oil pumpjacks nod lazily in the heat, and then you'll see it: a glittering palace rising out of the pancake-flat ground. The land here is mirrored: the choppy silver-blue waves of an immense solar array stretch out in all directions. In the distance, they lap at a colossal grey wall five storeys high and almost a kilometre long. Behind the wall, you glimpse the snaking pipes and gantries of a chemical plant.