Observations of present-day heatwaves show a very large increase in temperature, in fact, a similarly extreme heatwave 100 years ago would have likely been around 4C cooler.
Climate change made last week's record-breaking European heatwave at least five times as likely to happen, analysis suggests.
Rapid assessment of average temperatures in France and Toulouse between June 26-28 show a "substantial" increase in the likelihood of the heatwave happening as a result of human-caused global warming, the experts said.
Temperatures observations suggest the kind of extreme heat seen last week has become at least 10 times, and potentially 100 times, more likely since 1900, analysis from the World Weather Attribution group found.
Health
But the scientists said other factors were at play which affect temperatures, along with climate change, such as changes to land use, air pollution and irrigation.
Combining observations with models that compare today's world with 1C of global warming with what conditions would be without human influence suggests climate change made the heatwave at least five times more likely.
The analysis also suggests that such heatwaves are 4C hotter than a similar event would have been a century ago.
Top temperature records were smashed in parts Europe, including France which saw a new high of 45.9C (114.6F), more than 1.5C above the previous record.
But the analysis focused on the three-day average which includes night time temperatures as well as day time highs, has more impact on human health.
Extreme
For France temperatures averaged 27.5C (81F), and in Toulouse, chosen because some of the scientists involved were at a conference there at the time, it was more than 30C (86F) over that period.
The experts also warned a heatwave in June is potentially more serious for people as the holiday season has not yet begun and it is harder for people to avoid the highest temperatures.
Dr Friederike Otto, acting director of the environmental change institute at the University of Oxford and one of the experts behind the analysis, said: "This is a strong reminder again, that climate change is happening here and now. It is not a problem for our kids only."
"Both observations and models show a strong trend towards stronger heatwaves. However, the observed trend is stronger than the modelled one, and we do not yet know why."
Peter Stott, from the UK Met Office who is an expert in analysing the role of climate change in extreme weather, said: "Observations of present-day heatwaves show a very large increase in temperature, in fact, a similarly extreme heatwave 100 years ago would have likely been around 4C cooler."
Air
The analysis comes as Europe's Copernicus Climate Change Service (C3S) revealed that European average temperatures for June had been the highest on record for the month, with temperatures more than 2C above normal.
Globally June was also the hottest on record, with average temperatures outstripping the previous record for the month in 2016 by 0.1C.
Jean-Noel Thepaut, head of C3S, said: "Although local temperatures may have been lower or higher than those forecast, our data show that the temperatures over the southwestern region of Europe during the last week of June were unusually high.
"Although this was exceptional, we are likely to see more of these events in the future due to climate change."
The Met Office said the UK was spared the scorching temperatures seen in parts of Europe as a result of an "undercut of cooler air coming in from the North Sea".
Record-breaking
Weather balloon evidence showed the air 1.5km above Cornwall was 24.8C (76.7F) in the early hours of Friday morning, spokesman Grahame Madge said.
"Air is cooler aloft, so comparable values at ground level would have been much warmer.
"These extreme temperatures, possible reaching 40C (104F) by day, were prevented by an undercut of cooler air coming in from the North Sea.
"Without this cooling, easterly influence, we would undoubtedly have seen much higher values on the ground; most likely an extension of the record-breaking temperatures seen across continental Europe, where national June and all-time temperature records widely fell," he said.
This Author
Emily Beament is the Press Association environment correspondent.
