It is hardly news any more that heat records are being broken every summer. We knew this would happen in a warming world — and so it has. What is striking about the news coverage of the heatwave that has recently scorched parts of North America, is a general hesitancy to link it to climate change. This is particularly galling when science has shown that every heatwave we experience is now made more intense by human-induced global warming. Every single one. Including this week.
The most dramatic alterations in extreme weather events caused by human-caused climate change are in the rate and intensity of heat and cold extremes. Cold weather extremes are declining in frequency while heat extremes are increasing dramatically, with dire consequences for society.
It would have been virtually impossible for several devastating recent heatwaves to occur at the magnitude they did without climate change. Take the one in Japan in 2018, which hospitalized tens of thousands of people, or the one in Siberia in 2020, which caused wildfires and melted permafrost. Research by our team found this was at least 600 times more likely to have happened because of human-caused changes. We are still working on quantifying the effect of climate change during the heatwave this past week, but we anticipate similar results.
What to look for here is the order of magnitude. Climate change has also led to an increase in heavy rainfall in many parts of the world. For example, the downpour associated with the deadly Hurricane Harvey in 2017 was made about three times more likely because of global warming. Similarly, droughts in some parts of the world, for example in Cape Town, are becoming correspondingly more likely.
These changes are dramatic because our societies have adapted to a very stable climate over centuries. But they are far, far smaller than what we will see for changes in heatwaves.