Human-caused climate change made UK heatwave 10 times likelier, says study

Human-caused climate change made the recent record July heatwave in the United Kingdom 10 times more likely, a study released by the World Weather Attribution on Friday has found.

Studying the heatwave in the UK and the rest of Europe, scientists have found that this is a “conservative estimate’’ and that extreme temperatures have risen more than climate models have simulated.

Twenty-one scientists from South Africa, Germany, France, the Netherlands, Switzerland, New Zealand, Denmark, the US and the UK collaborated as part of the WWA network to assess to what extent human-induced climate change altered the likelihood and intensity of the heatwave.

On July 15, the UK Met Office issued, for the first time, an extreme-heat warning. In the following days, many weather stations across the country recorded their highest-ever temperatures, in many cases breaking previous records by three and four degrees Celsius. On July 19, Coningsby in Lincolnshire set a national record, with the temperature reaching 40.3°C, 1.6°C warmer than the previous record and 3.6°C hotter than the record that had stood until 1990.

The WWA study says that while exact data is not immediately available, there have been estimates of “hundreds of heat-related deaths’’. “Across the world, climate change has made heatwaves more common, longer and hotter,’’ said the study.

To quantify the effect of climate change on the high temperatures in the UK, scientists analysed weather data and computer simulations to compare the climate as it is today, after about 1.2°C of global warming since the late 1800s, with the climate of the past, and found the recent heatwave would have been 4 degrees cooler at pre-industrial levels (if the global temperature was 1.2 degrees less).

The WWA has also estimated that greenhouse gas emissions increased temperatures in this heatwave by two degrees Celsius. “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. 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.” Friederike Otto, a senior lecturer in climate science at the Grantham Institute for Climate Change of Imperial College London.

“These lines of evidence mean that globally, as a direct result of climate change, previously very rare heat is now just unusual. While, in some cases, events now considered ‘extreme’ reach temperatures that were formerly all but impossible. Long-term changes in heatwaves are influenced not only by globally well-mixed greenhouse gases but also by more localised influences, including aerosol trends, land use changes, vegetation and soil moisture changes, irrigation, and urbanisation effects,’’ said the study.