Across the Atlantic, 100 million Americans were urged to stay indoors in June as temperatures from California to Texas soared above 40°C. South-western states are in the grip of the worst drought for more than 1,000 years. Lake Mead and Lake Powell, the two largest American reservoirs, have been in drought conditions for more than 20 years and are now at their lowest levels ever recorded. The reservoirs, which are part of a system that provides water to more than 40 million people, are around a quarter full.