At their sweltering zeniths, British heatwaves exert strange and intriguing thermodynamic effects. Asphalt turns to liquid. Air becomes flame. Wheelie bins transubstantiate into single-player swimming pools. How, as temperatures rise again, can we cope? Authorities issue orders to drink water, stay in the shade, stay at home, use a fan and so on. One scientist even suggested coating windows with yoghurt. It’s easily spreadable, he argued, dries quickly, and can be removed with water and cloth. In straitened circumstances, the idea might make some sense. But it seems anachronistic that we must rely on fans, yoghurt and wheelie bins when, as much of the world has understood for many decades, the best defence against a heatwave is air conditioning. This relatively simple physical mechanism ha