Kilojoule burn in heat vs cold

A pram camper finished her outdoors workout on a warm Spring morning, with a pointed question: "do you burn more calories (or kilojoules) working out on a warm day compared to a cold one?"
"Hmmm, I replied, that's a tricky question." And here's why.

• Cold weather itself doesn't increase kilojoule needs. BUT your body does use a lot of energy to warm and humidify the air you breathe when exercising outside in the cold. According to sport nutritionist and author, Nancy Clark, if you were to burn 600 calories (equivalent to about 2,500 kilojoules) while cross-country skiing for an hour in zero degree weather, you may use an estimated 23 percent of those calories to warm the inspired air. But you use the heat you generate with exercise to warm the air you breathe and help stop your lungs from getting chilled. 

• You don't burn extra kilojoules in cold weather unless your body temperature drops and you start to shiver. And even then, what you may 'burn' depends on a number of different factors. When a person is shivering, the body needs to work harder to maintain body temperature). And studies have shown that shivering can burn about 400 calories (or 1680 kilojoules) per hour and it depletes glycogen stores and leaves you feeling tired. In this situation the energy expenditure in cold weather is greater than in warm weather, but the actual amount of additional calories burned due to shivering depends on the temperature, how long the person was exposed, and the type of clothing. (And considering that at pram camp you're not likely to be wearing a lot of layers or even shivering for much more than a few minutes, the extra 'burn' would probably be non-existent).
  
• If you sweat more, particularly during your workouts in summer, you won't burn extra kilojoules.You burn kilojoules when your muscles perform work. Sweating is just the way your body uses to regulate excess heat.