Greenhouse-gas emissions are increasing the frequency of heatwaves

EXTREME HEAT is ruinous to productivity, particularly if you are a criminal. Several American police forces posted messages to their social-media accounts last weekend declaring a moratorium on crime. “It is just too hot to be outside committing crimes,” wrote the Park Forest Police Department in Illinois, on its Facebook page. In some cases, it seems to have worked. “We have had zero customers stay the night at our ‘hotel’, so we appreciate all of the criminals adhering to the heat advisory,” tweeted the Malden Police in Massachusetts on Sunday.The messages came as scorching temperatures swept across America, placing more than 100m people under excessive-heat warnings. Temperatures hovered either side of 40°C on the east coast. On July 18th Mitch Petrus, a well-known retired player of American football, died of heatstroke after working outdoors all day. At least five other deaths have been reported.