Wouldn't that make people living in the northern hemisphere less likely to become fat?
These hypothetical cold fat burning technqiues, that I've seen, suggest inducing very mild hypothermia (shivering). That only happens rarely in the north.
Are you certain of that? It gets really cold here and everyone wears jeans. Only children wear winter pants casually. Sometime the air itself is cold enough to get you shivering.
The only time I see people correctly dressed against the cold is when they do winter sports or go hiking in the woods.
You seem to have never visited warm and cold climates...