The record temperatures in the UK last week would have been "almost impossible" without human-induced climate change, leading scientists have concluded.
The UK recorded temperatures above 40C for the first time on 19 July.
Without human-caused climate change these would have been 2C to 4C cooler, the experts say.
It is a taste of what is to come, they say, with more heatwaves, fires and droughts predicted in coming years.
The extreme heat caused significant disruption to the UK, with experts warning that excess deaths related to temperatures will be high. Wildfires also destroyed homes and nature in some places.
The world has warmed by about 1.1C since the industrial revolution about 200 years ago. Greenhouse gases have been pumped into the atmosphere by activities like burning fuels, which have heated up the Earth's atmosphere.
The findings are released by the World Weather Attribution group - a collection of leading climate scientists who meet after an extreme weather event to determine whether climate change made it more likely.
They looked at three individual weather stations that recorded very high temperatures - Cranwell, Lincolnshire, St James Park in London, and Durham.
Dr Friederike Otto of Imperial College London, who leads the World Weather Attribution group, told BBC News that even in today's climate, having such temperatures was still rare and that we would expect them between once every 500 years and once every 1,500 years.
But she said that as global temperatures rose, the likelihood of this heat happening more regularly would increase.
"We would not have had last week's temperatures without climate change, that's for sure," she said. These temperatures are at least 2C higher but the real number is probably closer to 4C higher than a world without human-caused climate change, she explained.
The scientists use a combination of looking at temperature records dating back through time, and complex mathematical models that assess how human-caused climate change affects the weather.
"Because we know very well how many greenhouse gases have been put into the atmosphere since the beginning of the industrial revolution, we can take these things out of the model and simulate a world that might have been without climate change," Dr Otto says.
That allows the scientists to compare the two different scenarios - a world with 1.1C of warming and a world without that temperature increase.
Dr Otto says if we want to keep this type of a heat a rare event, the UK must reach net zero "very soon". That is the point at which we stop adding to the amount of greenhouse gases in the atmosphere. The government's target is to reach net zero by 2050.
"Every little bit of warming really makes these types of events more likely and even hotter. Heatwaves are much more deadly than other extreme weather like floods and climate change is a game-changer for heatwaves," she explained.
The scientists also say it demonstrates that the UK is not adapted to warming temperatures, with our homes, hospitals, schools and travel networks unable to withstand the high temperatures.
Climate change is affecting all parts of the globe, with extreme heat this year affecting countries including India, the US, Australia, Spain and Germany.
Politicians globally are committed to keeping global temperature rises below 1.5C but environmentalists say progress is much too slow.
"The climate has already changed - we are and will continue to suffer the consequences of government inaction," Greenpeace UK's head of climate, Rosie Rogers, told BBC News. "How bad things get depends on how much or little governments now decide to do to get off fossil fuels."
"As one of the world's biggest historical emitters, the UK has an obligation to step up and rapidly slash emissions to zero," she said. "The new prime minister needs to act on these warnings from the climate, and set an example for others to follow."
To tackle climate change, scientists say we must make steep cuts to our emissions, changing how we produce and use energy, as well as protect nature that helps to soak up greenhouse gases.