How is the record-breaking US heatwave linked to the climate crisis?
Global temperatures have risen by an average of around 1.2C since pre-industrial times. However, temperatures over land are heating up more quickly than over oceans. Because of this, the western US has experienced around 2C of warming since the start of the fossil-fuel era  providing the backdrop for more extreme heat events, explains Dr Zeke Hausfather, a climate scientist and director of climate and energy at the Breakthrough Institute in California. The rising temperatures weve experienced in the western US over the last century make it a lot more likely that well have extreme heatwaves today, he tells The Independent. Weve seen more records fall in the western US in the last decade than any other decade in US history. Part of the reason for that is that the region has already warmed by around 2C since pre-industrial times, with around three quarters of that warming occurring since 1970.  As temperatures rise, heatwaves are becoming more frequent, intense and long-lasting, according to a growing body of research. A 2019 heatwave in Europe, which disrupted travel on the Eurostar, was made up to 100 times more likely by the climate crisis (Getty Images)  The study of how human-caused warming is influencing heatwaves and other types of extreme weather is known as event attribution. Scientists in this field have previously found that human-caused climate change made a 2020 heatwave in the Arctic more than 600 times more likely and a 2019 Europe-wide heatwave up to 100 times more likely. No formal assessment of the influence of the climate crisis on the current US heatwave has yet been carried out. However, previous research suggests that US heatwaves are now 3 to 5C hotter than they would have been without the influence of the climate crisis, according to an estimate from Dr Michael Wehner, a senior scientist at the Lawrence Berkeley National Laboratory. A study published in 2015 found that an exceptionally warm summer in Texas in 2011 was made around 10 times more likely by human-caused climate change. In addition, a second study published in 2019 found that a 2018 heatwave affecting the entire northern hemisphere  including the US, Europe and parts of Asia  would have been impossible without the climate crisis. Research also suggests that combined heatwave and drought events  known as dry-hot extremes  are also on the rise in the US as a result of the climate crisis. Such events provide the ideal conditions for the spread of wildfires, scientists have warned.