The fact that wind farms, solar farms and battery-powered vehicles are now cost-competitive does not mean they can be built at whatever pace politicians choose. They require raw materials—sometimes in prodigious amounts—siting permits, infrastructure for transmission, recharging and the like. They also need lots of capital. And the necessary materials, sites and capital are all, to various extents in different places, in short supply. The price of lithium has more than doubled in the past year. Copper prices are up by about 70%. Fights are breaking out over permits for new mines, wind and solar farms. Capital remains poorly allocated; while big companies rush for offshore-wind projects around Britain, poorer countries with rising emissions remain starved for investment. If efforts to ease those constraints fail, the world’s decarbonisation plans will stall instead of soar.