Tropical nights that once lasted 4 days now stretch to 30 as Europe swelters

Europe, gripped by record-breaking heat, has seen overnight low temperatures hit all-time highs and tropical nights surge in frequency, according to new analysis.

The Financial Times, citing research by the US climate group Berkeley Earth, reported Saturday that an analysis of weather records from June 19 to June 30 found overnight low temperatures reached all-time highs at hundreds of weather stations across at least 15 European countries, including those in northern Europe.

As many as 25 countries set new June records for overnight lows during the period. In France, the United Kingdom and Germany, more than half of the weather stations analyzed recorded their highest-ever June overnight temperatures.

In Kupschütz, east of Dresden, Germany, the overnight low reached 29.4 degrees Celsius on June 27, breaking the country's all-time record for overnight low temperatures.

Many local stations shattered their previous June records by a wide margin — by 4.9 degrees in Pirmasens, Germany; 5.3 degrees in Saint-Fargeau, France; and 4.2 degrees in Camborne, England.

Across most of Europe, a night is classified as a tropical night when temperatures do not drop below 20 degrees Celsius. Last month, most parts of France endured seven or more tropical nights, while the UK recorded five consecutive tropical nights — its longest such streak on record.

Mark McCarthy, a scientist at the UK Met Office, said tropical nights had historically been very rare across much of the European continent but were becoming increasingly common. "Climate projections suggest this trend will continue," he said.

A study published last month in the journal Nature Climate Change found that the average temperature of the 10 hottest nights of the year has been rising by 0.32 degrees Celsius per decade — a steeper increase than the 0.27-degree-per-decade rise recorded for the 10 hottest days.

Surging overnight temperatures are being observed in other regions, including Asia, but Europe appears to be experiencing the phenomenon with particular severity.

An FT analysis of data from the EU's Copernicus Climate Change Service covering the world's 500 most populous cities found that the sharpest increases in overnight temperatures were concentrated in southern and eastern Europe.

In some European cities, the hottest overnight temperatures have risen by more than 0.5 degrees Celsius per decade — more than double the overall global average.

Naples, Italy; Barcelona, Spain; and Athens, Greece have each gained roughly one additional tropical night per year since the 1970s. Milan recorded about three tropical nights a year in the 1970s; that figure has now climbed to around 33. Athens logged more than 100 tropical nights in 2024.

Tropical nights take a significant toll on the human body. Falling asleep requires core body temperature to drop by about 1 degree Celsius, and hot nights disrupt that process. They also prevent the normal nighttime decline in heart rate and blood pressure, as the body works to cool itself.

Lorna Powell, a physician who leads the climate action group Mothers Rise Up, said hot nights cause sleep disruption, dehydration and cardiovascular stress that can worsen underlying conditions — particularly in older adults. "Even during the June heat wave, we struggled to cope with a sharp rise in life-threatening emergencies, especially on the hottest nights," she said.

Dominic Royé, a climate scientist at the Galician Institute of Biological Research in Spain, said the body loses its chance to recover when temperatures fail to drop at night, meaning unusually hot nights affect mortality independently of daytime heat. His latest research found that extreme nighttime heat raises the risk of death by 2.6 percent globally.

Warnings are also emerging about the economic consequences. Cathy Bofman McCloud, CEO of the climate nonprofit Hera, said workers who suffer through tropical nights arrive at their jobs with impaired hand-eye coordination, "making mistakes and harming themselves and others."

One UK study found that sleep deprivation caused by high overnight temperatures costs the national economy the equivalent of 0.04 percent of GDP annually.