The UK heatwave in perspective

The frequency and severity of European heatwaves has increased in recent decades. As far as heatwaves go this one didn’t last very long and was nowhere near as destructive as the 2010 Russian event. Indeed the 2022 event, along with that in 2019, were very intense but short-lived and thus will probably not make it to the top European heatwaves when duration and areal extent is taken into account.

Last week the UK Met Office warned a heat wave was approaching and that there was a 50:50 chance of setting a new UK record of high temperature, possibly breaking the 40C barrier for the first time. They also gave the usual qualifications that although what they were predicting was within the bounds of natural variability they didn’t think it was natural variability but rather the result of a ‘disturbed climate.’ They also said we would see more heat waves in the future, and while the predicted event was estimated to occur about once every 300 years it might be once every 15 years or so by the end of the century. But whatever the statistics it was certainly an event that needed to be taken seriously.

The statistics of such events are frequently contradictory if not meaningless. The Met Office estimated that the probability of the heatwave had increased in the past ten years over a hundredfold. This, they claimed, was due to do the background temperature the heatwave was imposing itself upon. But this background hasn’t changed all that much in the past ten years, either regionally or globally as examination of the Met Office generated temperature data sets shows. In short, how such a huge difference in probability has occurred seems strange when set against similar temperatures in the UK and globally!

But wait, Justin Rowlatt, the BBC’s Climate Editor told us, it’s all straightforward. The heatwave is due to the Azores High pressure area that normally sits off Africa extending itself over the Iberian peninsula, France and up towards ourselves. Incidentally, the behaviour of the Azores High might be changing as claimed by a recent much debated Nature Geoscience paper that sees changes in the past 1,200 years. But he continued, all this is happening when the UK, and the world, has increased its background temperature by just over a degree, so it’s going to be bad. The IPCC has said that a one degree C increase in global temperature has led to a measurable increase in heatwave occurrence.

Of course there is more to it than this, it’s far too simplistic in its ignoring of natural variability and the assumption that the incidence of such events has a normal probability distribution who mean temperature is always rising and whose probability distribution is unchanging. Even given that average UK summer temperatures have increased by about half a degree in the past 80 years, this heatwave could still have occurred before. Indeed recent papers point to non-temperature influences on heatwaves in Europe such as changes in atmospheric circulation and even a correlation with colder sea temperatures in the North Atlantic, a correlation that researchers say has a predictive skill for the majority of recent European heatwaves.

Sunday was hot, Monday hotter and Tuesday intense. One could sense the whole nation enduring what it must and waiting for the predicted break on Tuesday evening. Wednesday is a normal day for this time of the year.

When it was all over the Met Office did a reverse ferret, as journalists say, and changed its stance once again. Now the breaking of the 40 C barrier was not something that could have happened under natural variability. Their Chief of Science and Technology, Professor Stephen Belcher, reflected on the UK breaching 40 C for the first time. He’d had a chat with his colleagues and they’d decided that it would have been impossible in an ‘unperturbed climate.’

The bottom line is that the climate is changing and the UK is (slightly) warmer today than many decades ago. We live in a warming world and thus can expect more heat waves in the future. Definite assertions about causes and predictions are fraught with complications and uncertainties that only more data will dispel. Whatever the case, more wind turbines or solar panel won’t do anything to help people cope with heat waves or prevent similar events in the future.