Since the turn of the 20th century, shortly after a version of the US Open first began, the average summer in New York has warmed by around 2°C. Annual average temperatures globally have risen by roughly half that. An even starker trend was evident at the Olympic games in Paris earlier this year. In the 100 years since the games had last been held there in 1924, the average temperature in the city in August has risen by 2.7°C.