Paris experienced its hottest ever day with the mercury topping out at 42.6C on July 25.

The record-shattering heatwave that baked much of northern Europe last month was likely between 1.5 to 3 degrees Celsius hotter due to manmade climate change, an international team of scientists said Friday.

The three-day peak saw temperature records tumble in Belgium, the Netherlands and Britain and the city of Paris experienced its hottest ever day with the mercury topping out at 42.6C (108.7 Fahrenheit) on July 25.

The ferocious heat came off the back of a similar wave of soaring temperatures in June, helping that month to be the hottest June since records began.

Scientists from the World Weather Attribution team combined climate modelling with historical heatwave trends and compared it with in situ monitoring across the continent.

They concluded that the temperatures in the climate models were between 1.5-3C lower than those observed during the heatwave in Europe.

"In all locations an event like the observed would have been 1.5 to 3C cooler in an unchanged climate," the WWA said, adding that the difference was "consistent with increased instances of morbidity and mortality."

Global warming also made the July heatwave in some countries between 10-100 times more likely to occur, compared with computer simulations.

Such temperature extremes in northern Europe, without the additional 1C centigrade humans have added to the atmosphere since the industrial era, would be expected on average once every 1000 years.

"Climate change had therefore a major influence to explain such temperatures," the WWA said.

The July heatwave caused widespread disruption, prompting train cancellations and emergency measures in many cities. Several heat-related deaths were reported, though a precise toll is likely to take weeks to materialise.

The June heatwave itself was likely made at least five times more likely by climate change, and was around 4C hotter than an equivalent heatwave a century ago.

"Models are very good at representing large-scale seasonal changes in temperatures," said Friederike Otto, acting director of the Environmental Change Institute at the University of Oxford.

"On localised scales, climate models tend to underestimate the increase in temperature."

Hottest Europe summers

Europe has experienced exceptionally intense heatwaves in 2003, 2010, 2015, 2017, 2018 and two this year, peaks consistent with the general warming trend: the four hottest years on record globally were the last four years.

Martha Vogel, a climate researcher at the Swiss Federal Institute of Technology in Zurich who was involved in the WWA research, said it was "virtually certain" that Europe's 2018 heatwave -- which sparked widespread wildfires -- could not have occurred without climate change.

Vogel and the team in a study published last month found that just 2C of warming -- levels aimed for in the Paris climate deal -- would see a 2018-style heatwave happen every year.

"The five hottest European summers -- 2018, 2010, 2003, 2016, 2002 -- were all in this century," she told AFP.