It's a finding that is destined to start a new round of arguments over the aircon remote.

A new study covering more than 1.6 million people has revealed that 22 degrees is the perfect air temperature to live in.

A city with an average annual temperature closer to 22 tends to have a population who are more agreeable, conscientious, emotionally stable and extroverted.

The study is observational, and does not show cause-and-effect. But the scientists behind it theorise that better weather leads people to leave the house more often, leading to more social interaction, which encourages a friendlier personality.

Melbourne, with an annual average temperature  of about 15 degrees, is well-below that temperature. Even Sydney only averages about 18 degrees. You have to go all the way up north to Rockhampton and Townsville to hit the sweet spot.

The findings help explain why colder and warmer countries tend to produce people with different personalities, says Professor Samuel Gosling, a University of Melbourne academic who worked on the study.

They also suggest that as the world continues to warm, there are likely to be subtle shifts in human personality.

"We know personality traits vary across geographic regions," Professor Gosling says. "We also know that these geographic personality traits are associated with a broad range of consequential outcomes, including economic activity, for example entrepreneurial start-up rates, crime rates, health behaviours, health outcomes and voting behaviour.

"So learning about the role of personality in potentially influencing these outcomes is of great interest to anyone who wants to affect these outcomes."

About 40 per cent of your personality is determined by your genes. That leaves 60 per cent to be determined by your environment, says Professor Nicholas Haslam, an expert in personality psychology from the University of Melbourne.

Warmer environments encourage people to go outside, where they are more likely to meet new people. That encourages them to develop a socially acceptable personality – agreeable and conscientious. Warmer climates also make people feel more positive in general.

Research has long pointed to 22 degrees being the Goldilocks temperature for humans – not too hot, not too cold. "It is the least taxing temperature  for the body to regulate its own temperature," says Professor Haslam.

And it is well-established that personality traits differ between countries.

The research team, made up of Australia, American, Chinese and British researchers, speculated the two might be linked.

To test this they gave online personality tests to 5587 Chinese students and 1.66 million Americans, and compared the results to the average annual temperature where they grew up.

The tests measured personality along five well-studied characteristics: agreeability, conscientiousness, emotional stability, extraversion and openness to new experiences.

In both groups the researchers found the closer a town's average annual temperature was to 22 degrees, the more its population exhibited those personality characteristics.

However, the findings were much stronger for the Chinese group than the Americans studied, cautions Professor Haslam.

"Temperature does not play a dominant role, it plays a role. The effects are fairly weak. You would not want to say it is the single dominant cause of personality."

The study was published in Nature Human Behaviour on Tuesday.