Extreme heat across large tracts of the Northern Hemisphere has raised fears for crops in China, fuelled forest fires in Portugal and Russia's Far East, forced flight cancellations in the Southwest US, and melted tarmac on roads in Britain.
As Wednesday marked the summer solstice - the longest day of the year - forecasters said temperatures in Paris were expected to hit 37 Celsius, Madrid could see 38C, and London was set for 34C with warnings of thunderstorms.
Rounding up the record temperatures set in the past two months, the World Meteorological Organisation (WMO) said the Earth was experiencing "another exceptionally warm year" and the heatwaves were unusually early.
"Parts of Europe, the Middle East, North Africa and the United States of America have seen extremely high May and June temperatures, with a number of records broken," the WMO said late on Tuesday.
The trend seen during the past two months has put average monthly global temperatures among the highest ever recorded since data began to be collated in 1880.
A study published earlier this week found that nearly one in three of the world's people were already exposed to potentially deadly heatwaves and predicted that number would rise to nearly half by the end of the century unless governments take steps to aggressively reduce climate-changing emissions.
"People are talking about the future when it comes to climate change, but what we found from this paper is that this is already happening ... and this is obviously going to get a lot worse," said Camilo Mora, geography professor at the University of Hawaii at Manoa and lead author of the study published in the Nature Climate Change journal.
