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Despite a brief respite from the heat, the UK is still in the middle of a stretch of unusually hot weather. Over the past two weeks, temperature records have been smashed all over Europe and beyond as patches of high pressure across the northern hemisphere led to sweltering conditions.
In the UK on June 28, Glasgow experienced its hottest June day ever, with temperatures of 31.9 centigrade that started melting the roof of Glasgow Science Centre. In Ireland on the same day Shannon hit the highest ever recorded temperature when thermometers topped 32 centigrade, while on July 4 Tbilisi, Georgia, broke its all-time record with a temperature of 40.5 centigrade.
Temperature records were also set across North America with Denver, Mount Washington, Burlington and Los Angeles in the US tying or breaking heat records while Montreal on July 2 recorded a temperature of 36.6 centigrade – its highest in 147 years of record-keeping.
To put things mildly, then, it’s been a hot couple of weeks. But is this stretch of toasty weather a direct consequence of global warming, or are we just experiencing the usual vagaries of our unpredictable weather? The answer, it turns out, is a little bit of both.
Unpredictable weather
It’s impossible to point to one hot summer as evidence of climate change, says Edward Hanna, professor of climate science and meteorology at the University of Lincoln. “You just can’t link individual events to climate change,” he says. “There’s a lot of natural variability [in weather] and we’re talking about seasonal changes which are always variable to some degree.”
It’s particularly difficult pinpointing the cause of weather in the UK, since the country sits right at the confluence between different air masses. In the case of this heatwave, a southerly wind blowing across the Iberian peninsula and France carried warm air up from southern Europe while a patch of high pressure sitting over the UK kept the skies almost entirely free of cloud.
This competing network of air masses makes predicting the effect of global warming on the UK somewhat tricky. We know that since 1970 the Earth’s average temperature has been growing by around 0.17 centigrade per decade, but climatologists are struggling to model what impact this will have on the jet stream, the winds high in the atmosphere that brings patches of weather over the Atlantic towards the UK. “They simply can’t predict changes in the jet stream accurately enough over the next few decades,” Hanna says.
Despite the natural variability in weather patterns, Hanna says that there is something strange about this recent patch of hot weather. “It’s almost getting to drought-like conditions in many parts of the country,” he says. In Lincoln, where Hanna works, there hasn’t been any significant rainfall since June 11. “That’s actually quite unusual and I think we’re all increasingly aware of that.”
Things are heating up
Even though it’s not possible to draw a direct link between climate change and this year’s heatwave – or even the cold snap earlier this year – it seems that these kinds of extreme weather events are becoming more common. “It is true that [the heatwave] is a sign of things to come locally,” says Ted Shepherd, a climatologists at the University of Reading. “We expect more and more warm temperatures to be coming.” As the average temperature across the globe keeps rising, the amount of time we spend above 30 centigrade will inevitably also rise.
But beyond that, it’s hard to know how climate change will impact the UK. Take the cold snaps earlier this year as an example. “These cold events are still a puzzle,” Shepherd says. It could be the case that as the climate warms, there’s more exchange between cold Arctic air and warmer air in the lower latitudes, and this could make it more likely that the UK will experience extreme cold snaps.
In other places, it’s likely that increased air temperature is linked to extreme rainfall. In the contiguous United States, the number of places hit by extreme one-day rainfall has been steadily increasing since the 1930s. The northeastern coast of the US is also regularly plagued by winter snowstorms, and there’s already some evidence that links warmer Arctic temperatures with an increased frequency of those storms.
In the UK, however, there is only one near-certainty. Summers are likely to be hotter and heatwaves – when they do happen – will be more scorching. “It’s clear that there is a long term trend on that,” Shepherd says. “Because of climate change we will get more hot summers in general, and this is a good example of what’s going to come so it’s a good opportunity to think of our resilience and if we’re ready for such a thing.”
Updated 14.07.2018: An earlier version of this article said that two of the UK's hottest summers had happened since 2007. It should have referred to two of the UK's wettest summers since 2007.
This article was originally published by WIRED UK
