So you’ve cheered up at our first glimpse of sun in two years? Well, that’s what you think. Research shows that hotter isn’t happier, and that a few degrees can turn a heatwave into a crimewave

THE FEELING OF bare feet in warm grass, the coconutty smell of suntan lotion, the sight of little kids frolicking in the paddling pool – what’s not to love? Summer has, at last, arrived in Ireland. Previously whey- coloured, sun-starved faces take on a fetching glow, men across the nation dig out their three-quarter-length camouflage-print shorts, and there’s a collective holiday feeling in the air.

But does the good weather truly make people happier? Most of us seem to work on the assumption that mood and weather are intrinsically linked. So just as we expect to feel rather low and bleak in cold, rainy November, summer sunshine makes us giddy as goats.

It seems that this popular logic is not too far off the mark, at least according to psychologist Lance Workman. He says that sunshine is “nature’s Prozac”, stimulating the production of mood-boosting serotonin in the brain. It appears that good weather gives us (temporarily) sweeter dispositions. Workman says that we become more trusting and optimistic, and more likely to leave a bigger tip in restaurants.

But higher temperatures may also have the opposite effect, leaving us sweaty, hostile and potentially violent. The optimum range for feeling loved-up with the world is 19 to 24 degrees, but once the mercury creeps higher, trouble may ensue. At that point, people “need greater personal space and they have less patience if others invade it”, says Workman. “From 24 degrees to 30 degrees, the crime rate rises for every one-degree rise in the temperature.”

An unusual series of laboratory tests by criminologist Ehor Boyanowsky showed just how irritable excessive heat can make us. In one test, researchers subjected volunteers to a series of either insults or compliments, and volunteers were invited to get their own back by giving electric shocks to the researchers. At temperatures of more than 33 degrees, volunteers became so maddened by the heat that they fired off shocks even when the researchers were paying them compliments.

In the real world, however, crime starts to decrease at very high temperatures. Even criminals feel the need to flop out in the shade, it seems.

And while warm sunshine and bare, tanned shoulders may make our thoughts turn to love, friskiness quickly evaporates once it gets too hot. “That anyone should care in this heat whose flushed lips he kissed, whose head made damp the pyjama pocket over his heart!” flapped narrator Nick Carraway in Scott Fitzgerald’s The Great Gatsby, suffering the effects of a blistering New York summer that even a copious quantity of mint juleps couldn’t alleviate. Forget romance – once you’re really sweltering, all you can think about is getting cool again.

NOT EVERYONE IS convinced of the link between summer sun and soaring spirits. A German study last year came to the counter- intuitive conclusion that weather has only a minimal effect on mood. Daily mood questionnaires were completed by 1,233 participants over the course of one month, and these were then compared with data from the German Weather Institute. The study found that while bad weather made people feel slightly worse, they were impervious to the effects of wall-to-wall sunshine.

And surely, if warm sun truly does make people cheerier, then the serotonin-rich inhabitants of Mediterranean countries must be much happier than their counterparts in the (usually) dank and drippy north? Not so. A report last month by the Paris-based Organisation for Economic Co-Operation and Development (OECD) showed that people from northern European countries are the happiest and most satisfied with their lives. Denmark, Finland, and the Netherlands, with their healthy work-life balance and low unemployment rates, came top of the list, while Ireland performed creditably, slipping in at number five. Sunny France, Italy and Spain, meanwhile, didn’t even make it into the top 10. In fact, the Italians were deemed the most miserable Europeans of all, showing that even sun-saturated Tuscans get the blues.

The sudden onset of summer can bring its own pressures. Here in Ireland, having been cheated of sunshine for two years running, we’re tortured by the thought that this early bout of Mediterranean weather may be the only summer we’re going to get. So we spend every available moment outside, soaking up the sun, resenting anything – work, shopping, school – that takes us away from the precious beams.

And that in itself can leave you in a hot, bothered and distinctly irritable mood.