When you breathe in cold air, your body warms up that air. Simultaneously, your body temperature will lower slightly but then eventually come back to its basal temperature of $\sim$98.6$^\circ$ F (37 $^\circ$ C). Your body must expend energy to raise the temperature back up. I was thinking about this and wondered: How many calories do we burn just by raising the temperature of cold air that we breathe in?
