[Retric]

There are a few adaptions to colder conditions like Brown Fat and shivering which directly converts calories into heat and work fairly well.

Body Size and insulating fat at can also make a huge difference. People in warmer climates are simply less adapted to cold conditions and therefore at greater risk for a given temperature.

PS: Some people can actually walk around without clothing or becoming cold in 40f weather and be perfectly comfortable. It's sleeping that's the greatest risk as you reduce metabolic activity while having a large surface area in contact with the ground.