Below, Trevor Harley shares five key insights from his new book, Head in the Clouds: How the Weather Affects Our Minds and Mental Health.
Trevor is Emeritus Professor of Psychology at the University of Dundee in Scotland. He is the author of several books on psychology, language, and consciousness.
What’s the Big Idea?
Your mind doesn’t exist apart from the weather—it exists within it. Light, temperature, rain, wind, and the changing seasons quietly shape your mood, behavior, and mental health in ways most of us never notice.
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1. The weather affects mental health.
Seasonal Affective Disorder, or SAD, is a form of depression with a seasonal pattern, usually appearing in autumn or early winter and lifting in spring. People with winter-pattern SAD often feel low, lethargic, sleepy, and hungry in the winter months. They may crave carbohydrates and put on weight. They feel as if someone has turned down the light inside their head.
I suffer from it myself, and perhaps that is not surprising. Where I live in east Scotland, in midwinter the sun creeps over one hill at about 9:30 in the morning and sinks behind another at about 3:00 in the afternoon. The day feels as if it has barely started before it is over.
This lack of winter light is an important cause of SAD. We need light to help set our biological clock: the internal timing system that regulates our circadian rhythms, especially the sleep-wake cycle. Morning light is particularly important in helping our bodies understand that the day has begun. Light is what scientists call a zeitgeber—literally a “time-giver”—an external cue that helps keep the body’s clock in step with the outside world. Bright light affects melatonin production, the hormone associated with sleepiness, and interacts with other systems involving cortisol and serotonin. The whole process is not a simple switch, but an intricate dance of hormones, neurotransmitters, sleep, light, genes, behavior, and expectation. When the dance goes wrong, our mood suffers.
“Morning light is particularly important in helping our bodies understand that the day has begun.”
I think of seasonal low mood as a continuum. At one end are people with severe, debilitating winter depression. In the middle are people with the “winter blues.” Then there are some people who are not bothered at all. Others even experience the reverse pattern: low mood, agitation, insomnia, or anxiety, in summer. While winter SAD may be linked to too little light, summer-pattern depression may involve too much light, too much heat, disrupted sleep, and a sense of being overwhelmed by the season everyone else seems to be enjoying.
Temperature matters too. Many of us function best in moderate conditions, around 21°C, or 70°F. When it becomes very hot, mental health can suffer. Hospital admissions for mental and behavioral disorders rise during periods of high temperature. Heat can worsen sleep, increase irritability, and make distress harder to regulate. Cold is more complicated. For some people, cold weather is invigorating. A cold, bright winter day can feel wonderfully clarifying. Some carefully controlled forms of cold exposure are being studied for possible psychological benefits. But cold can also be painful, frightening, and dangerous.
There is no one kind of weather that is good and another bad. Our minds are embodied—not floating in a sealed container. They are affected by light, heat, cold, wind, rain, pressure, humidity, and the rhythms of the seasons.
2. Weather affects behavior in surprising ways.
There is a cultural stereotype that sunny, warm, dry weather is “good,” while cold, wet, cloudy weather is “bad.” But not everyone agrees. Some people love heat. Some dread it. Some people come alive in spring while some prefer autumn. Some feel soothed by rain. Some find wind unbearable.
Just as we differ in personality, we differ in what we might call weather personalities. This helps explain why research on weather and mood has sometimes produced inconsistent results. Seeking averages across everyone may miss the fact that the same weather has different effects on different people.
Still, some patterns are clear. Hot, humid weather tends to make people more irritable. It is associated with aggression and violence. When people are overheated, sleeping badly, and physically uncomfortable, self-control becomes harder. Some studies suggest that small increases in temperature are associated with measurable increases in violent crime. There is even data suggesting that hot weather can affect speech, making it simpler and less fluent.
“Hot, humid weather tends to make people more irritable.”
Weather also influences judgment. Sunshine can make us more expansive, sociable, and creative, while cloudy or rainy weather may make us more careful, analytical, and detail-focused. Consider a university open day: on a sunny day, prospective students may pay more attention to sports fields, social life, and attractive surroundings. On a gray day, they may pay more attention to libraries, laboratories, and academic facilities. The weather has not changed the university, but it has changed the frame through which people see it. Weather alters what seems important, what we notice, what we remember, and how we interpret other people.
Rain has its own psychology. The smell after rain, called petrichor, can be deeply evocative. For many people, it is emotionally powerful and may lift mood, though the science of exactly why remains complicated. The sound of rain can also be calming. A rainy day can give us permission to slow down, stay in, read, write, or just think. Intense wind, by contrast, has long been associated with irritability, restlessness, and unease. But then a gentle breeze on a hot day can bring enormous relief and delight. Our response to weather is not purely rational. It is shaped by language, memory, culture, and emotion.
3. We can change our behavior.
Weather can make us feel like passive participants. It is something that happens to us. We cannot command the sun to shine or the wind to drop. But we are not helpless. We can learn our own patterns: notice what weather unsettles us, what restores us, and what makes us productive.
If you know heat makes you irritable, you can avoid important discussions on oppressive afternoons. If you know winter darkness lowers your mood, you can treat light as a daily necessity rather than a luxury. If you know rain helps you concentrate, you can use rainy days for careful work.
This is not pretending that bad weather is wonderful. It is a form of acceptance: seeing clearly what is happening, then choosing how to respond. We shape our environments, and our environments shape us. We cannot control the weather, but we control more than we think.
4. The season you were born in may matter.
People born at different times of year have experienced different conditions in the womb and in early infancy: different amounts of daylight and temperature, different infections circulating in the population, different maternal vitamin D levels, and different diets. It would be surprising if none of these things had any lasting effect.
Research has found associations between winter birth and later risk of some psychiatric conditions, including schizophrenia, bipolar disorder, and major depression. Most people born in winter will not develop these conditions, but the pattern is there at the population level.
“We are seasonal creatures before we are even aware of the seasons.”
There is also evidence linking season of birth with later temperament and personality traits. Again, the effects are small, but they remind us that we are seasonal creatures before we are even aware of the seasons. Light, temperature, infection, food, sleep, biology, climate, and weather are woven into development from the beginning.
5. We should be in awe of the weather.
Some of my most vivid memories are weather memories. I remember being terrified as a child by the brilliant flash of lightning and the roar of thunder. I remember making a snowman with my uncles during the severe winter of 1962–63. I remember skies that have stopped me in my tracks, the strange silence after snow, rare clouds, crepuscular rays, and much more.
If we are just a little receptive, weather gives us awe for free. Awe is the feeling we have when we encounter something vast that exceeds our ordinary frame of reference. It can make us feel small, but not diminished. It makes us feel connected: to nature, time, other people, something larger than ourselves. Growing evidence shows that awe can benefit mental health.
The weather is one of the most accessible sources of awe. You do not need to travel to the Grand Canyon; you can simply look up. You can watch a cumulonimbus cloud building on a humid afternoon. Stand under a clear winter sky full of stars. See sunlight break through after rain. Watch snow transform an ordinary street into another world.
Living in better sync with the seasons does not mean romanticizing hardship. The weather is not always benign—it can be lethal. There is inconvenient weather and there is dangerous weather. But there is also meaningful weather, beautiful weather, restorative weather, and weather that teaches us about ourselves.
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