Ciudad Real, central Spain, July 17, 11pm: outside it’s 32.8ºC, according to the AEMET Spanish state meteorological agency. At that temperature the bed sheets cling, pajamas are too heavy, and cool air is notable by its absence. It’s impossible to sleep. Your first reaction is to turn on the air con, if you have it. But often it’s not worth the cost to have it running the whole night, so you decide to turn it off again.