How the weather affects our moods

This time last year I lived in London, which was good in some respects. For example, it gave me excellent access to Four Tet’s £5 all-nighters, and I love Four Tet because he’s a big ol’ music nerd whose DJ selections are memorably, brilliantly eclectic and also frequently segue into Sweet Like Chocolate, the best/worst UK garage track of the 1990s.

my set at Brixton tomorrow will just be that new @floatingpoints 10 times in a row and then sweet like chocolate
— Four Tet (@FourTet) March 21, 2014

London also had many downsides, some of which have only become apparent now I live in Manchester and have escaped its gravitational pull. It’s incredibly expensive, its houses appear to be made of cardboard, and one is never entirely free of the fear of seeing Boris Johnson astride a bicycle.

How long before Boris appears???

But the worst thing, the absolute worst thing, was the weeks-long period of hot, dry weather in the summer of 2018. The UK is not a nation that copes well with heat, or snow (with the honourable exception of Scotland), or wind, or pretty much anything other than ‘vaguely overcast and slightly breezy’, so it was pretty awful everywhere in this country. In London, however, there was not even a breath of wind, both my work and my home were poorly insulated, and it reached 40 degrees Celsius in the Underground. I couldn’t cool down anywhere, so I couldn’t sleep, so I was extremely grouchy for an entire month.

So that’s one example of the weather affecting mood! Let’s look at research on people who are not me to get a broader picture.

It’s complicated

Since climate varies all around the world, and also because it’s not a good idea draw conclusions about what all humans are like on the basis of who is easily available to take part in psychology studies (the WEIRD problem), I have tried to gather together information from studies done in a variety of countries. Nonetheless, because there are more studies available about people in Europe and North America than on other continents, take what I say with a pinch of salt.

Temperature and hours of sunlight (that is, number of hours when the sun is out, not hours of daylight) came up time and time again in the studies I looked at, but not always in the same way. Over the whole year in Germany [i], higher temperature and less sunlight were associated with more negative mood. Between September and February in Estonia [ii], higher temperature was associated with more intense feelings, both positive and negative, while more sunlight was linked to more positive feelings. In springtime Japan [iii], sunlight hours didn’t correlate with mood, but maximum happiness happened when the temperature was 13.9 degrees Celsius and tailed off either side of that!

Some of this variation in findings is perhaps due to the different temperatures at the times and in the places that these studies were conducted. In the German study, people were probably experiencing temperatures ranging between -1 degree and 26 degrees Celsius, while the people in the Estonian study were getting somewhere between 1 and 4 degrees and the people in the Japanese study getting between 9 and 17 degrees.

Estonia is, thankfully, much warmer in the summer

You might be thinking, surely there’s another problem here because people don’t tend to go outside much when it’s really cold so they’re not necessarily experiencing those temperatures, and you would be right to do so. I found a study [iv] about people living in the northern United States that tackled this head on, and they found that people who spend more than 30 minutes outdoors have improved moods in higher temperatures, but this is the reverse for people who spend less than 30 minutes outside – and yes, they checked that it wasn’t just that people who are in a better mood anyway tend to spend more time outside. There was another problem, though: they only did the study in spring, when people generally like spending time outdoors because it’s starting to warm up. To combat this, they looked at people in the southern US, northern US/Canada, and Europe (which have different climates and latitudes) at all different times of year. They still found the relationship between being outdoors, higher temperature and better mood – but only in spring, and only in the people at higher latitudes, presumably because spring in the southern US can get unpleasantly hot in a way it doesn’t in the other places they looked at. In fact, the people in the southern US tended to be in a worse mood as the temperature increases.

Sunshine and blue sky through a branch of spring blossom

The researchers who did this study thought there might something special about warm-but-not-hot spring weather that prompts us to be in a better mood, and I can’t say I disagree.

And that brings us to… seasonal affective disorder

Seasonal affective disorder, or SAD, is a type of depression that turns up just at one time of year and leaves you alone the rest of the year, like a bad friend who only comes around in summer because you have a garden and they don’t. Though SAD can happen in the summer [v], it’s most common in winter and appears to be triggered specifically by the decrease in day length rather than a drop in temperature or sunlight hours [vi].

This being the case, you’d think that SAD would be worse among people living at higher latitudes because there’s more variation in day length across the year, and that’s true for people living in North America – but not for people living in Europe [vii]. It’s not clear why that’s the case, but some possible explanations are that there are cultural differences in willingness to talk about psychological problems or that climate plays a role, since, for example, New York and Barcelona are at the same latitude but have very different climates.

The average high temperature in Barcelona in January is 15 degrees Celsius. In New York, it’s 4 degrees Celsius.

There’s also a theory that people living at particularly high latitudes might have evolved some kind of resistance to daylight-related changes in mood [viii], but the evidence I have seen about this is conflicting: one study on people in Tromsø (a city in Norway that’s in the Arctic circle) that shows no seasonal variation in depression [ix], and another comparing people in Tromsø with people in Accra (the capital city of Ghana, near the equator) that found a small shift in depressive mood with the seasons for people in Tromsø but not people in Accra [x]. Since a study on mood and day length in people in the UK [xi] found that shorter days were associated with low mood in women but not in men, even within a single city you may get different results depending on who you ask.

So maybe there’s a genetic factor, but there are other theories too [viii]. Maybe people with SAD have circadian rhythms (24-hour repeating cycles of events in the body like core temperature) that are out of sync with the sleep/wake cycle, or maybe people with SAD react differently to the dip in serotonin (the ‘good mood’ brain chemical) that happens in everyone in winter. These theories aren’t mutually exclusive, and since treatments based on the circadian rhythm idea work for some people but not others, it seems likely to me that different people could have different reasons underlying their SAD.

For the wrap-up, let’s look at something different but still not very cheery (sorry). Here’s a weird fact:

If Florida had been just a little warmer on 7th November 2000, Al Gore would probably have become President of the USA

The weather is quite low on the list of Things I Would Change About The 2000 US Presidential Election To Make It Better If I Could Time Travel And Were Omnipotent but nonetheless, it’s on there. Bear with me while I explain. This is based on a study about US presidential elections between 1960 and 2016 which mapped results by state against what the weather was like in that state on voting day [xii]. In the US, voting happens in November, which is a cold, let’s-stay-in-and-watch-TV time of year in much of the country. So, generally, as temperature rises, so does voter turnout. However, those voters that wouldn’t otherwise have come out behave in a very specific way compared to people who were going to vote no matter what: they are likely to vote for the incumbent party (that was Al Gore’s party, in case you have forgotten), less likely to vote for the challenging party, and less likely still to vote for an alternative party like the Greens. In Florida, that might have been enough to give Gore a clear lead.

Argh.