A new study has revealed the most intense heatwaves ever across the world – and remarkably some of these went almost unnoticed decades ago. The study, which calculated how extreme heatwaves were relative to the local temperature, showed the top three hottest-ever in the respective regions were in Southeast Asia in April 1998, which hit 32.8 °C, Brazil in November 1985, peaking at 36.5 °C, and Southern USA in July 1980, when temperatures rose to 38.4 °C.