The U.K.’s heat wave earlier this month fueled so many blazes in London that the city’s fire service was busier than any day since Nazi attacks during World War II. More than 840 people may have died in England and Wales, according to a preliminary analysis.

Now, a rapid scientific analysis of the event concludes that without climate change those conditions would have been "extremely unlikely.”

World Weather Attribution, the research team that conducted the study, looked at the weather in the southern half of the country on July 18 on 19, analyzing both peak temperatures and two-day averages. The analysis, released Thursday, found greenhouse gas pollution made the heat wave at least 10 times likelier and 4 degrees Celsius hotter than it would have been.