Large swathes of southern and eastern Europe were placed on heatwave red alert on Tuesday and the World Meteorological Organization (WMO) warned of an increased risk of deaths as extreme weather gripped the continent, Asia and the United States.
The Mediterranean island of Sardinia could see highs of more than 47°C and forecasters said temperatures could hit 40 degrees in several Italian cities, including 42-43°C in the Lazio region that includes Rome.
With baking temperatures hitting Europe during the peak summer tourist season, the WMO said the heatwave in the northern hemisphere was set to intensify. An estimated 61,000 people may have died in heatwaves last year in Europe alone.
The EU's emergency response coordination centre issued red alerts for high temperatures for most of Italy, northeastern Spain, Croatia, Serbia, southern Bosnia and Herzegovina, and Montenegro.
Heatwaves this summer, which saw temperatures climb to 53°C in California's Death Valley and over 52°C in China's northwest, have coincided with wildfires from Greece to the Swiss Alps and deadly flooding in India and South Korea.
They have added fresh urgency to talks this week between the United States and China, the world's top greenhouse gas polluters.
US climate envoy John Kerry met Chinese officials in Beijing and expressed hope that climate cooperation could redefine troubled ties between the two powers.
Chinese President Xi Jinping stressed Beijing's commitment to carbon neutrality and a carbon peak was certain but that it would not be influenced by others.
"Temperatures in North America, Asia, and across North Africa and the Mediterranean will be above 40°C for a prolonged number of days this week as the heatwave intensifies," the WMO said.
Overnight minimum temperatures were also expected to reach new highs, the WMO said, creating the risk of increased cases of heart attacks and deaths.
"Whilst most of the attention focuses on daytime maximum temperatures, it is the overnight temperatures which have the biggest health risks, especially for vulnerable populations," it said.
The heat in Europe could also prompt a lasting shift in tourist habits, with more people choosing cooler destinations or travelling in spring or autumn, tourism organizations predicted.
