Stubbies in winter: Are South Islanders really tougher in the cold?

This week's cold snap has sent the mercury plunging and reignited the same old argument that resurfaces each winter: are South Islanders really tougher in the cold?

It's a running joke across the country — that Aucklanders start shivering and reach for the puffer jacket the moment temperatures dip, while those further south are still walking around in shorts and jandals as frost settles on the ground.

For many New Zealanders, the unofficial cold-weather rivalry starts somewhere around the Cook Strait, with some claims that real winter only begins once you get south of Timaru.

Dunedin, Invercargill and Southland residents have long worn their ability to shrug off freezing mornings as a badge of honour.

But is there actually anything behind the stereotype?

University of Otago physiologist Jim Cotter says the science paints a more complicated picture.

"People don't show a great deal of adaptation to cold. They psychologically deal with it better, but they still feel the cold. They're just less bothered."

Cotter told 1News the biggest factors in cold tolerance had little to do with latitude and more with what people were made of.

"It very much depends on who you are. If you're larger, you've just got more mass to produce heat. And you've got more mass to surface area. So you're physically shaped better to be able to deal with cold."

Bigger people also carried more muscle, which was more metabolically active, while a layer of subcutaneous fat acted as insulation.

"If you have a look around, the people who dress more lightly are the bigger people. It's just the way that they thermoregulate."

That went some way to explaining the image of the Southland farmer working outside in stubbies on a frosty morning.

"They're working hard and they're not moving through the air that quickly, so they're not having a lot of heat forced out of them," Cotter said.

"They prefer not to wear much because they have to unload the heat."

The same principle applied to endurance athletes, with world records in endurance events typically set in cool conditions because runners could push harder without wasting energy offloading heat.

Cotter said studies had shown that people from different climates could accurately gauge their own temperature, but their comfort thresholds sat in completely different places.

"You put two people in a room, one from the tropics, one from the high latitudes, and they'll both be able to accurately tell you whether they're warm, cool or neutral," he said.

"But the one from the tropics isn't used to being cool, so they'll feel uncomfortably cool. And the one from the high latitudes isn't used to being warm, so they'll feel uncomfortably warm. They're both uncomfortable and for opposite reasons."

He said the same effect played out, on a smaller scale, between Auckland and Dunedin.

The annual temperature difference was about four to five degrees, rising to six in winter. But the daily experience was more stark.

"Dunedin's maximum daily average is not much more than Auckland's average daily minimum, so there's a critical difference in terms of how that makes you feel."

While repeated cold exposure might trigger some physical changes, Cotter said the effect was modest — and the biggest adaptation was likely to be psychological.

"Their behaviour helps too, in terms of choosing the right clothing."