The Psychology of Weather

Trevor Harley

• Publisher: Routledge
• Year: 2018
• Print ISBN: 9780815394846
• eBook ISBN: 9780429681998
• Edition: 1
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

Do you feel happier on a sunny day? Are you afraid of thunderstorms? Are you dreaming of a White Christmas?

The Psychology of Weather explores our relationship with the weather, and how it can affect our mood, behaviour, and lifestyle. The book sheds light on our preoccupation with this natural phenomenon, providing insights into how the weather on the day we were born can directly affect our intelligence and personality, and explore such surprising findings that suicide rates peak in the spring and summer.

When the weather affects everything from our buying behaviour, to the jobs we do, The Psychology of Weather shows us that understanding and appreciating the weather can improve our well-being and contribute to human survival.

1
Weather and Mood

Introduction

Psychology and the weather? How on earth do these things go together?

The weather affects much of what we do. It determines what food we can eat, and not so long ago whether there was food we could eat at all, whether there is water for drinking, growing crops, raising animals, and cleaning readily available, whether we are likely to be inside or outside, and how comfortable we feel. Air conditioning is only a recent invention, and of course is still unavailable in much of the world. Life and civilisation could develop on Earth only because the temperature, the amount of water, and the composition of the atmosphere lay within certain happy values. Weather affects us profoundly; it is a matter of life and death, and so it shouldn’t be surprising that it has an enormous role in our lives. As psychology is the science of why we behave as we do, it is then only natural that psychologists should be concerned with the weather and how it affects our behaviour. On reflection the only surprise is that psychologists haven’t been more concerned with the weather.

The weather might affect us in more subtle but still important ways. When it is a warm sunny spring day, we believe our souls sing, so we hurry outside, and according to Alfred, Lord Tennyson, in his poem “Locksley Hall”, “a young man’s fancy lightly turns to thoughts of love”. As winter deepens we feel gloom descend upon us, and we sit shivering in the darkness, depressed and yearning for summer. Or at least many of us think we do. Does the weather really affect our mood and our everyday behaviour? Does it affect mental illness – are we more likely to be seriously depressed when the weather is dull and gloomy? Are children born in summer at an advantage? Surprisingly little is known in answer to these and other questions; this book tries to answer them.

Science, Psychology, and the Weather

The weather interacts with psychology in three ways. First, there’s how the weather affects us. Second, there’s what our beliefs about the weather reveal about us. And finally when we come to study the influence of the weather on us, the weather provides an excellent environment for how to do psychology.

Often to the surprise of a first-year student, psychology is a science, and mostly an experimental science. In hot summers murder rates and ice cream sales both increase. Does one cause another? Do some people become psychotic killers after eating a vanilla and strawberry cone? That explanation sounds rather unlikely, but clearly there is something to be explained. This finding is an example of a correlation: as one thing changes, so does another. But, as we are fond of repeating to our students, a correlation by no means implies causation: it – probably – isn’t the ice cream sales causing the murder rate to go up (or vice versa – a satisfied murderer reaches for an ice cream cone). In this example it’s quickly apparent that a third variable, high temperature, is responsible for the increase in both ice cream sales and incidence of violence. A moment’s more reflection suggests that perhaps it isn’t even necessarily the high temperature that’s responsible; maybe it’s some other variable correlated with high temperature, such as excessive sunshine, or people getting sunburned and becoming irritable and on a short fuse, or high humidity plus high temperature, or even some other hidden variable that we can’t immediately imagine. Just observing stuff makes it difficult to work out what is causing something; for that, we need to carry out controlled experiments.

In a psychology experiment we assign participants randomly to experimental groups, and we try to keep as much as possible constant except for the experimental manipulation of interest. That way we can draw conclusions about causation with confidence. Suppose we kept one large group of randomly selected people in a very hot room and another similar group of people in an identical room but at a low temperature. We leave them alone for half an hour and then come back and find that the people in the cold room are talking away amicably to each other, while everyone in the hot room is fighting, or even worse, a couple of people have been murdered. We might then reasonably conclude that higher temperatures make us more aggressive, particularly if we can repeat or replicate this finding several times.

Unfortunately the weather doesn’t lend itself to being involved in controlled experiments because we can’t, as yet anyway, manipulate it directly reliably. We can’t make it hot and sunny in one place one day and then cold and dull the next (and even if we could we would have to be careful with our conclusions, as we have changed two things at once there, which is rarely a good idea). We can’t shift thousands of people from a desert climate to the tundra to study what changes, such as whether the murder rate goes up. The best we can manage at present is increasing the probability of rain in a particular location by seeding the clouds by spraying them with small particles, such as of silver iodide, and even this manipulation has limited success. As we can’t carry out controlled experiments, we must rely on observational correlational studies, where we look at what people in different climates do differently. With a bit of thought we can be a bit clever, such as looking at hot days in cold climates or cold days in hot climates, but our options are clearly limited.

All these factors make the weather an interesting but difficult topic for studying psychology in the real world empirically because it is so complicated, but also because we have plausible intuitions about how phenomena are related, and for once we have masses of data. It is scientifically challenging to ask: how can we draw sound conclusions with complex setups where many things are going on and changing at the same time? It is fortunate that there is a lot of weather and many, many people upon which the weather is acting because we can anticipate that we are unlikely to find very large effects on behaviour due to meteorological variables, or else these ideas would be enshrined in law, and every time hot weather is forecast there would be a red warning for psychopathic killers at large. It’s likely that effects are small, and therefore we will need to be alert to possible confounding variables, and we should always remember that we are at best constructing arguments based on limited data.

The study of psychology and the weather is a microcosm of psychology; as we shall see, all the major debates present in the social sciences are present here.

Climate and Personality

Before we go any further we must distinguish between climate and weather. The climate of a region is the “average” weather over a long period of time. We can’t choose too long a period because climate changes, so the standard measure is the average over 30 years.

The weather is what is happening now. We might be living in an area with a hot, dry, sunny desert climate, but today it happens to be snowing heavily. The long-term hot, dry pattern is the climate, and the snowing today aspect is the weather. Weather and climate comprise several variables, including temperature, humidity, wind direction, wind speed, precipitation type, and atmospheric pressure, but these variables are not independent – for example in the northern hemisphere, northerly winds generally correspond to lower temperatures, and southerly winds to higher, and falling pressure is associated with higher precipitation rates. A climate is defined by a pattern of scores on these variables: a desert is dry, a rain forest hot and wet, and a temperate climate doesn’t score at the extremes very often on any of the variables. Importantly the dominant type of vegetation varies with climate – you won’t find many rainforests growing in a cold, dry tundra. The climate is made up of average weather.

The best-known classification of climates is the Köppen scheme, named after the Russian-German weather scientist Vladimir Köppen (1846–1940). He divided climates into five broad groups: tropical, dry, temperate (a big group varying from Mediterranean to Highland), continental, and polar, each broad group having several subdivisions. So northwest Europe is Cfb (temperate without dry season and having a warm summer); the northeast US is Dfa in the south (cold continental without dry season and having a hot summer) and Dfb in the north (cold continental without dry season and having a warm summer); and North Africa is BWh (arid desert and hot).

Surely people who live in sunny, warm climates are happier, more relaxed, and more easy-going than those of us born into a dark, cold climate? Surely mental illness, particularly depression, is less common if the sun is always shining?

The problem with testing this idea is that many things vary systematically with climate. By “systematically” we mean that if we change one thing, something else nearly always changes as well. Let’s consider just the weather of particular places: desert climates, for example, are dry, sunny, and hot, but which of those three factors, or combination of them, might affect our behaviour? And then very cold climates are further north (and south, although not many people live in Antarctica), where we observe dramatic variations in the length of daylight – perhaps it isn’t the cold that gets to people, but the lack of sunlight in winter, or perhaps it’s both?

Even more complex are cultural differences that might vary with the climate. For example, as a very general rule, the nearer the equator you get the hotter it gets, but the greater is the proportion of people living in poverty or extreme poverty. But perhaps the poverty is in part a consequence of the climate; it seems very plausible to me that if it is too hot, people are unable to work as much and as hard, and so productivity and the gross national product decline. And if it’s too dry, crops will be more difficult to grow, and so crop failures and famine will be common. Of course money isn’t everything, and possibly money comes at the cost of happiness, but starvation is bad no matter how happy you might be.

We believe that there is an optimum climate, with a mean temperature around 22°C, without extreme variation and without too many violent weather events, such as big storms, droughts, and heatwaves. A location can, however, have an average temperature of 22°C, but that average can occur because it is pretty much 22° all the time (very nice, particularly if it’s a little cooler at night), or because it’s 35° in the summer and beneath freezing for much of the rest of the year (not so nice). Precipitation can come as rain or snow; we can have 1000 mm distributed pretty evenly across the year (nice), or with much of it falling in one or two “monsoon months”, and very dry the rest of the time (troubling). So in addition to the average of the meteorological variables, the range and distribution matter too, and together they determine the climate.

A person’s personality is those more permanent aspects of the way in which he or she behaves. An extravert tends to be outgoing and sociable, and an introvert less so. There are many ways of measuring human personality, but one of the most robust and most used schemes to have emerged in recent times is the “Big Five” model. When we measure personality, we ask people to take personality tests, which contain many questions where you have to score how you feel on statements such as “I would rather go to a party than stay in reading a book”. If you look at how many people respond to personality tests, many minor aspects of personality can be clustered together to form the five independent personality dimensions of openness (how open you are to new experiences), conscientiousness (self-explanatory), extraversion (how outgoing you are), agreeableness (how altruistic and kind you are), and neuroticism (how anxious and irritable you are). These dimensions helpfully form the acronym OCEAN. Scores on personality variables need not be completely static across a person’s lifespan: I am sure I have become slightly more extravert as I have got older; and they may change slightly across situations: a glass of wine makes me more extravert. However, in contrast to a person’s mood, personality is relatively stable.

The meteorological variable that has most effect on personality is variation in temperature. Two large-scale studies by Wei and colleagues looked at how people scored on personality tests across many areas of China and the US. They found that the average ambient temperature during someone’s youth was related to scores measuring the “Big Five” personality variables. Temperature particularly affected scores on the openness factor, particularly finer-grained measures of socialisation (how well a person internalises society’s norms) and personal growth (how open a person is to new experiences). One obvious possibility is that such climate enables developing individuals to explore the external environment, hence influencing their personality development. Essentially it’s easy for children to wander around exploring the outside world if it’s nice all the time, and less easy if they’re snowed in for half the year. Within the US these constraints mean that if all other things are equal (a big if), a child growing up in southern California is likely to be friendlier, more outgoing, and more inquisitive than a child growing up having to deal with the brutal winters of Minnesota (in spite of the many advantages of that beautiful state).

I should reiterate the caveat that this research is correlational, as we can measure only the effects of climate on variables of interest, and it is worth repeating that climate varies with many other factors, such as geographic and regional genetic variations, culture, levels of disease and poverty, and history. Also the differences we find are small, and of course many other things are going on as well. A warm, sunny climate by no means guarantees an outgoing child.

Climate and Intelligence

Individual differences include personality, gender differences, and intelligence. Are there other individual differences that vary with climate? It has been known for some time that temperature affects the sex ratio of reptiles through a thermosensitive period of egg development; in many species of turtle, eggs in cooler conditions hatch as male, and eggs in warmer as female. Perhaps surprisingly weather and climate may affect the human sex ratio, with a study in Japan showing more girls being born in warmer weather and hotter climates. Other studies suggest that it isn’t just warmer weather as such but more extreme weather that increases the ratio of female births, with one possible mechanism being that male foetuses are more susceptible to external stressors, including extreme weather. However, the results across several studies are not totally clear-cut: one study found that more boys were born in spells of warmer weather in northern Finland. One explanation is that the variations have to be relatively extreme to reduce the number of boys, as was the case in Japan, but not in Finland.

At present we are talking about relatively small differences, with the birth ratio varying from about 1.04 boys for every girl to 1.07, but if the climate changes to produce global warming and more extreme weather, the ratio will change more, with more females being born than males, at least until evolution has time to catch up with any changes. We already observe dramatic changes in the ratio of male to female sea turtles in Australia, with up to 99% of births in some areas being female. It’s unlikely that boys will disappear altogether, but in some parts of the world male births are already valued more than female births, and this problem could be exacerbated.

Intelligence is conventionally measured by IQ (intelligence quotient) tests. Authors of these tests now proclaim them to be “culture-free” (i.e., they don’t ask you questions such as who won the World Series in 2013 and declare you dumb if you don’t know). A great deal of research has shown that average IQ varies around the world, both across nations and within them. Many studies have found that both IQ and measures of attainment in school vary with climatic differences between geographical locations such that, essentially, the colder the climate, the higher the IQ of the resident population. Harsh winters are good for the population’s intelligence.

The cross-cultural variation in IQ is surprisingly large, with a mean IQ score ranging from 64 in Mozambique to 108 in Hong Kong. We observe effects within countries as well as across them, such as in the United States. Massachusetts, New Hampshire, and Vermont have higher average IQ, and California, Louisiana, and Mississippi have lower scores.

Of course climate is not the only variable likely to have an effect on IQ here, but statistical analyses show that it does make a clear contribution: too hot leads to lower IQ. Why might this be? The theory of cold winters proposes that survival in colder climates poses two evolutionary problems that would have required high intelligence to solve: finding food and keeping warm. Many of the arguments involved are speculative, and the obvious answers are not necessarily right. On finding food, one argument is that hunting in the grasslands of Europe and Asia was more difficult than hunting in the woodlands of Africa because grasslands provide less cover; however, humans evolved in the relatively open savannah, not in dense forests. The peoples of the Arctic endure the harshest winter conditions of all, and by this sort of argument should have a very high IQ, but the average IQ of Arctic people in these studies was rather low, at 91, although it’s been noted that Arctic peoples have a very strong visual memory. Another argument, proposed by Satoshi Kanazawa, is that evolution favours high IQ as we go further from the evolutionary origin of humans in sub-Saharan Africa; staying put is the lazy option, while exploring new environments is more intellectually taxing.

None of these arguments is that convincing, and they all leave a slightly unpleasant taste in the mouth because there is no certainty that the studies adequately take into account the obvious reasons for cross-cultural variation in IQ scores: differences in the culture’s attitude and experience with the tests, education, poverty, colonialism, nutrition, and disease. The argument that factors such as geography and climate are important because you find effects within a country such as the United States is fallacious because different areas of the US show wide variations in income, education, and disease. Few things drive psychologists into a frenzy as much as the suggestion that there are possible differences in any kind of aptitude relating to race.

Some recent studies have found that levels of infectious disease affect IQ, controlling for the effects of education, national wealth, temperature, and distance from sub-Saharan Africa; in particular parasite load is particularly important: children with heavy intestinal worm infestations tend to have lower IQs. Parasite loads affect the strength of the immune system, in that if the body is expending so much energy fighting off parasite infections, other systems are likely to be compromised. (There is some evidence though that very low parasite loads might be good for the immune system, perhaps we are now in the west too clean.)

There are some less controversial differences in cognitive skills that vary with climate. Many languages of the world (English is not one) use tone, or pitch, to give meaning to their words. The American linguist Caleb Everett and his collaborators have found that languages with complex tones, those that use several pitches for making contrasts in meaning, are much more likely to occur in humid regions of the world, while languages where pitch doesn’t make much difference to meaning occur more frequently in drier regions. The favoured explanation is that inhaling dry air causes the larynx to become dehydrated and reduces the elasticity of the vocal chords. So it’s physically more difficult to achieve complex tones in dry climates, especially cold ones.

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Table of contents

• Cover
• Title
• Copyright
• CONTENTS
• Preface
• 1 Weather and mood
• 2 Weather and health
• 3 Weather and behaviour
• 4 Weather and belief
• 5 Weather and society
• Further reading