here's an example of the variance in wattage and caloric burn as a temperature variable is applied. Air density is higher and requires greater wattage, as does temperature regulation for the body.
72℉ = 83% of the effort of -25℉ as the images indicate
http://www.kreuzotter.de/english/espeed.htm
Wind is another wattage variable as well. Play with the site and see your results!
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. “He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.”- Fredrick Nietzsche
"We can judge the heart of a man by his treatment of animals." - Immanuel Kant