A heat dome is trapping warm air from northern Africa under a high-pressure system, causing temperatures in western Europe to reach levels usually seen in midsummer. Scientists say human-caused climate change is the main reason this event is so intense.
According to the United Kingdom's Met Office, Monday was the hottest May day ever recorded, with temperatures reaching 34.8 degrees Celsius (94.6 degrees Fahrenheit) at Kew Gardens in southwest London.
This was two degrees higher than the previous May record. The agency expects temperatures to drop later in the week.
Met Office meteorologist Greg Dewhurst told Agence France-Presse (AFP) that the rise in extreme temperatures is "a good indication of climate change in action" and is likely to become "the new norm."
In France, the national weather agency Meteo-France said Monday was the hottest May day since records began. Paris reached 33 degrees Celsius, including at the Roland Garros tennis complex during the French Open.
Some regions could see highs of 36 degrees Celsius on Tuesday, and the heat is expected to last through the week.
French authorities said that at least seven people have died from heat-related causes as of Tuesday, including five drownings.
Many people went to the beaches because of the warm weather, even though lifeguards are not scheduled to start working in many coastal areas until July.
A beach-goer in Anglet told AFP he was being extra careful with his young children because of the dangerous currents along the Atlantic coast.
Government spokesperson Maud Bregeon confirmed the number of deaths on TF1, saying: "What I can say today is that there have been seven deaths directly or indirectly related to the heat."
On Monday, Bergerac in western France reached 34.7 degrees Celsius, and Nantes and Angers had similar temperatures.
Spain's State Meteorological Agency (Aemet) warned that unusually high temperatures will continue across the country through the week, except in the Canary Islands.
Southwestern Spain is expected to have hot nights starting Wednesday, with peak temperatures between 36 and 38 degrees Celsius through Friday.
In Italy, the Lazio region, which includes Rome, approved new rules on Monday that limit outdoor work involving long sun exposure between 12:30 p.m. and 4:00 p.m.
Ireland also saw record May temperatures, with 28.8 degrees Celsius recorded at two weather stations, according to Met Eireann.
In Scotland, a grass fire started near Arthur's Seat, a hill near Edinburgh, as temperatures in the city reached 25 degrees Celsius.
An April report by the European Copernicus Climate Change Service and the World Meteorological Organization found that since the 1980s, Europe has warmed at twice the global average rate. The report also said that heatwaves have become more frequent and severe in at least 95 % of Europe.
Scientists say that rising greenhouse gas levels from human activity are making extreme weather events, such as heatwaves, droughts, and floods, occur more often and with greater intensity.