How heat influences mood, memory, and mental health
updated on Jul 21, 2026
There’s a reason the weather is such a natural conversation topic. In his fascinating new book, Professor Trevor Harley explores the psychology of weather, drawing on research and personal experience to make sense of how it affects our minds and mental health. In this extract, he examines why some people struggle in the heat while others thrive – and what might be going on below the surface
As part of my research into the effects of the weather I often conduct surveys by social media, which canvass my family, friends, colleagues, acquaintances, weather friends, former students, and people interested in my work, of all ages and nationalities. I don’t claim the samples are completely representative but they still give revealing results. When I asked the question, ‘Do you like hot weather?’ I was surprised by how few people said they did. I had begun my survey thinking I’d be swamped with people saying they loved hot weather, but most said they dreaded and despised it. People reported feeling uncomfortable as soon as the temperature goes much above 21°C (69.8°F), particularly if they have to do something that involves physical or even simply mental exertion. Only a few respondents admitted to really liking it, and even they had good reasons. George, a gardener, was wholly positive about natural heat. He is a cheery soul who looks as though he has spent most of his life outdoors, and I should say he lives in Scotland, so he rarely has to work in hot weather. One person who initially said he liked hot weather then admitted he really only liked the thunderstorms that sometimes come with it. Most people who took part in my hot weather survey, however, were like my friend Peter’s grandmother, who used to say simply, ‘I like it nice.’ The only reason some people actively sought out hot and humid conditions was in order to take a sauna.
Our attitude to heatwaves is changing. I remember the extraordinary British summer of 1976 being characterized as a light-hearted, even enjoyable event, with headlines in the popular press such as the legendary ‘Phew! What a Scorcher!’ – although those who were forced to draw their drinking water from standpipes may not have regarded it in this way. Now we view heatwaves more negatively. An analysis of newspaper articles in the United Kingdom from 1985 to 2023 confirms that there has been a shift in opinion, with the press no longer characterising heatwaves as occasions to enjoy an ice cream or jump in a fountain, but using increasingly apocalyptic language to describe them. Awareness of the dangers of climate change has grown greatly over the years and journalism reflects this shift.
Hot heads: heat and thinking
Heat affects the way in which we think. A number of research studies have shown the negative effects of higher temperatures on cognitive processing. They indicate that the ill effects really become significant at temperatures over around 30°C (86°F) – and well before physiological hyperthermia sets in. A 2024 large-scale study of over 50,000 participants in China found that exposure to high temperatures produces effects similar to the cognitive decline that often comes with advanced ageing, on measures of both verbal and mathematical ability. In this study a ‘high’ temperature was defined as greater than 32°C (89.6°F). The effects are cumulative in that the longer people are exposed to the high temperatures, the greater the cognitive decline. A 2025 study of almost 12,000 children aged around ten in the United States found that during heatwaves both learning and memory are negatively affected. The effects are intensified by lower socioeconomic status because poorer families have more limited means of ameliorating the effects of heat – for example, they are less likely to have air-conditioning.
It isn’t just our abilities to think and reason that are affected by heat; our language processing is, too. A study of seven million parliamentary speeches by 28,000 politicians across several countries, including the United States, the United Kingdom, Germany, and New Zealand, found that on hot days, defined as over 27°C (80.6°F), politicians use grammatically simpler sentences. Older politicians are particularly affected by the heat. The researchers said that it was as though during hot days we lose about a month’s worth of our language education.
Exactly why heat affects cognitive processing is not fully understood. One possibility is the dehydration that accompanies heat, another is disturbed sleep, and a third is prolonged stress, all of which are known to affect cognition. Although we might not fully understand what is going on, we can conclude that because our reasoning and decision-making might be suboptimal during heatwaves, it’s best not to make any big decisions at such times, if we can avoid doing so; by the same token it’s also advisable to scrutinise decisions made by others when it’s hot – including those of politicians.
The upside of heat
In my social media survey, many people who said they disliked hot weather did nevertheless find some good things to say about it. Moderate heat is pleasant, and even warmer temperatures are fine as long as we don’t have to do too much, which is why so many of us choose to go on holiday to places like the Mediterranean or Florida. Hot weather means being able to cook, eat, and drink outside, wear less clothing, and enjoy warm evenings with friends and family. That’s my experience too: for me it’s the warm evenings that are the best bit of a hot summer. Warm weather encourages us to be outside, exercise more, be more sociable, and have more contact with nature – all huge positives for our mental health. Hot weather also gives us the opportunity to practise gratitude, which we know is good for mental health.
Instead of cursing whatever the weather is, I search for positives. I think about all these good things the hot weather brings. If it’s too hot I remember all the times during the winter when I would open the front door to take my dog for a walk, only to be confronted by a blast of cold air that made me want to go straight back in, when I would think, ‘I wish it was summer already.’ When summer does finally arrive, don’t waste it.
‘Head in the Clouds: How the Weather Affects Our Minds and Mental Health’, by Professor Trevor Harley, DK RED, £16.99, out now.
