The UN climate chief has said that a record-breaking early heatwave scorching a swathe of western Europe was "a brutal reminder of the spiralling impacts of the climate crisis".
The UK and France have reported their hottest ever May days this week as a "heat dome" brought sizzling temperatures more typical of midsummer to western Europe.
He also noted extreme conditions gripping India, where troops are battling forest fires and local authorities have reported deaths from heatstroke.
International air-quality monitoring platform AQI recorded that the top 45 hottest cities in the world were all in India at midday on Wednesday, all above 43°C.
"Protecting human lives, businesses and economies from extreme heat and the many other soaring costs of climate change is core business for every nation, and it starts with kicking the fossil fuel addiction much faster," Stiell said.
The Middle East war had also laid bare the "soaring costs" of fossil fuel reliance and the need to pivot to cleaner sources of energy, he added.
French authorities on Tuesday reported at least seven deaths linked to the heatwave -- five of which were drownings, as many people sought relief at water spots.
Authorities in Britain said four teens had drowned in England since Sunday.
France and the UK both logged their hottest-ever May day on Monday and then again on Tuesday.
Ireland also reported record-breaking temperatures for May, while Spain, Italy and Austria have also experienced unusually sweltering conditions for this time of year.
