The UK's recent heat wave was the Great British Bake Off that no one wanted -- and it was made at least 10 times more likely by human-caused climate change, a new analysis shows.
But the World Weather Attribution project, which carried out the analysis, also said that its findings are likely to be an underestimate, warning that the tools available to scientists have limitations and are creating a blind spot to just how much of a role humans are playing in heat waves.
The tougher question to answer is: "By how much?"
To determine human influence on extreme heat, scientists use a combination of observations and climate models, or simulations. While models are often conservative in their findings, observed extreme heat in western Europe increased much more than estimated by the models.
"While models estimate greenhouse gas emissions increased temperatures in this heatwave by 2˚C, historical weather records indicate that the heatwave would have been 4˚C cooler in a world that had not been warmed by human activities," WWA said in a press release. "This suggests that models are underestimating the real impact of human-caused climate change on high temperatures in the UK and other parts of Western Europe. It also means that the results of the analysis are conservative and climate change likely increased the frequency of the event by more than the factor of 10 estimated by the study."
The UK last week experienced high temperatures that climbed over 40 degrees Celsius (104.5 degrees Fahrenheit) for the first time on record on July 19, hitting 40.3C in the English village of Coningsby. The British government issued its first-ever red level extreme heat warning for several parts of England, including the capital, London.
As temperatures soared, the country's infrastructure buckled. Train tracks bent out of shape; an airport runway melted; London's fire brigade declared a "major incident" as a number of fires broke out, in what the service said was its busiest days since World War II.
"In Europe and other parts of the world we are seeing more and more record-breaking heatwaves causing extreme temperatures that have become hotter faster than in most climate models," said Friederike Otto from the Grantham Institute for Climate Change at Imperial College London, who leads the WWA project.
"It's a worrying finding that suggests that if carbon emissions are not rapidly cut, the consequences of climate change on extreme heat in Europe, which already is extremely deadly, could be even worse than we previously thought."
Every fraction of a degree of global warming will bring worsening impacts of the climate crisis. The world has already warmed around 1.2 degrees Celsius on average, and there is a growing consensus that humans must try to keep warming to 1.5 degrees to avoid tipping points, where some ecosystems that the Earth relies on for its ecological balance may struggle to recover.
The scientists said the model results also indicated a heat wave as intense as last week's in the UK is "still rare in today's climate," with a 1% likelihood of it happening each year. However, once again weather records suggest the computer simulation results are conservative and similar extreme heat events are likely to occur more frequently as well.
In response to the publication of the new WWA analysis, Dr. Radhika Khosla from the Oxford Smith School of Enterprise and the Environment, praised the scientists for their speed.
"By carrying out rapid analysis based on established, peer-reviewed methods the WWA team are able to get evidence-based results into the public domain while we can all still remember the major disruptions from last week's extreme heat. This is the latest in a series of studies that all show the same result: climate change makes heatwaves more likely and more intense," Khosla said.
"The level of heat the UK is now experiencing is dangerous: it puts strain on our infrastructure, economy, food and education systems, and on our bodies. As the study points out, many homes in the UK become uninhabitable in extreme heat. Adapting to rising temperatures, building heat resilience with sustainable approaches, and protecting people is an urgent priority as unprecedented temperatures become the norm."
Peter Stott, a science fellow in climate attribution with the UK's Met Office, said this won't be the last time the country will be forced to deal with such extremes.
"Temperatures above 40C will occur again, possibly in the next few years and very likely over the next few decades," Stott said. "Only by curtailing greenhouse gas emissions can we reduce the risks of such extremes becoming more and more frequent."