Heat brain: why does hot weather make us so feral?

“I love England in a heat wave. It's a different country. All the rules change,” muses Leon Tallis, in Ian McEwan’s Atonement. “It was always the view of my parents that hot weather encouraged loose morals among young people,” says Leon's mother, Emily, in response. “Fewer layers of clothing, a thousand more places to meet. Out of doors, out of control.”

Of course, as the reader knows, the scene is dripping in dramatic irony: as Leon and Emily waffle on about the heat, sexual tension simmers between the novel’s two protagonists, Cecilia Tallis and Robbie Turner – tension which boils over and is consummated against a library bookshelf just a few pages later.

Extreme heat is often a backdrop to some of the most chaotic shows of passion or madness or violence in literature. In Shakespeare’s Romeo and Juliet, Mercutio is killed in a brawl when the Verona heat gets “mad blood stirring”. Centuries later, in The Great Gatsby, Daisy Buchanan suggests they “telephone for an axe” to break down the oppressive walls of their suffocatingly hot hotel room, moments before the ugly details of her affair with Gatsby come to light. In André Aciman’s Call Me by Your Name, set under a baking Italian sun, Elio masturbates with a peach which his lover, Oliver, eats afterwards. It’s an idea embedded in our language too: we talk of acting in the “heat of the moment”, of getting “hot under the collar”, of being “hot-blooded”.

It’s not just pathetic fallacy, either. In the 19th century, analysis found that violent crimes peaked in the summer months, while riots and civil disturbances typically happen in warmer times too. During the heatwave of 2018, police reported that 999 calls were up 40 per cent in some areas. “The public react very strangely when the weather gets hot,” the chair of the Police Federation told the Independent at the time.

It’s why Love Island can only work under a blazing, Balearic sun, and even the ‘winter’ version has to take place during the South African summer months. I just don’t believe Ekin-Su would have crawled onto that balcony or Andrew would have “sucked Coco’s tit or whatever” if they were holed up in an Alpine log cabin. The heat just does something to our brains that makes us inexplicably horny and unhinged.

With a heatwave sweeping the UK and temperatures set to reach staggering highs of 43 degrees, many of us are feeling similarly deranged. Maybe you had a Calippo for breakfast this morning. Maybe you texted your toxic ex. Maybe you impulsively Amazon Primed a paddling pool even though you live in a two-bed flat with no outdoor space bar a poxy balcony. Tom* tells me he kissed a woman more than ten years his senior at the weekend – which he describes as “very out of character” for him. “I feel like I need to make the most of the summer – it’s like the sun is making me go rogue,” he tells me. Layla, meanwhile, tells me she got “so horny” during the warmer months last year that she organised an “impromptu sex party”. It’s heat brain: when the hot weather clouds our judgement, lowers our inhibitions, and generally makes us a little bit feral.

All this begs the question: why? Does the sun literally melt our brains? Not quite – but almost. Professor Trevor Harley, Emeritus Professor of Psychology at the University of Dundee and author of The Psychology of Weather, explains that weather has always had a direct impact on our mood. “Sunshine has several beneficial effects on humans. First, there is the production of Vitamin D, which is involved in the production and release of serotonin. Sunshine also boosts the levels of nitric oxide, which dilates the blood levels and reduces blood pressure,” he says. “There’s no doubt that our expectations play a role too. What could be more pleasant and mood-elevating than sitting outside in the warm shade with a cool drink in hand, watching the bees and butterflies? Nature in itself is good for us.”

Admittedly, Brits in particular are also a little excitable when it comes to hot weather. In 2021, the average daily temperature in July was 17.6 degrees – warm, sure, but not that warm – and so the second the temperature lurches above 23, our confused brains start to think we’re on holiday, and before you know it you’re drinking a pre-mixed Pornstar Martini can even though it’s 2pm on a Tuesday. “Heatwaves are relatively uncommon in the UK, and novelty is an important factor,” Professor Harley says. “Many people do get excited and many do want just to make the most of it. Just look at the pictures of crowded beaches when the sun comes out.”

And, in our defence, it’s well documented that British heat is particularly humid and febrile – far more mania-inducing than the drier European climate. “Increasing temperature can make people feel stressed, which releases cortisol, and activates our stress response,” Professor Harley explains. “But increasing strength of sunshine and increasing temperature usually do go together so we see all these effects combine and interact in rather complex ways.”

“Heatwaves are relatively uncommon in the UK, and novelty is an important factor. Many people do get excited and many do want just to make the most of it. Just look at the pictures of crowded beaches when the sun comes out” – Professor Trevor Harley

On a more serious note, Britain is fundamentally unable to withstand soaring temperatures. Much of the country’s infrastructure was built in the Victorian era when soaring temperatures and flash floods were uncommon; now, although the climate is rapidly changing, our buildings and travel networks are not. This is having tragic consequences: in 2020, three people lost their lives after a train derailed as a result of extreme heat damaging rail tracks. 

Although this is an extreme example, there’s evidence that Britain’s failure to prepare for rising temperatures is already affecting the majority of us. Around 20 per cent of homes in England already overheat in the summer, and a 2021 report by the climate change committee found that since its 2016 assessment, more than 570,000 new homes had been built that were not resilient to high temperatures with little ventilation and copious amounts of glazing. This is compounded by the cost of living crisis, where using an electric fan is an unjustifiable expense for many people.

With this in mind, it’s hardly surprising that hedonism and recklessness are on the up in this heatwave as we hurtle towards climate disaster. As Allison P Davies wrote in her viral essay from earlier this year, A Vibe Shift Is Coming: “With the pandemic and climate change, our aesthetic and [behaviour] are certainly shaped by a sense of doom. There’s a nihilism to the way people dress and party; our heels get higher the closer we inch to death.”

It makes sense: now that mass extinction is on the cards, why shouldn’t you make a jug of Aperol Spritz just for yourself? Why shouldn’t you take your top off in public? And in the short term, realistically, it’ll be raining again in a month’s time – so we might as well enjoy it while it lasts.

*Name has been changed