The body consumes (burns) more energy to perform a given task in the cold than it does in the heat. Don’t believe me? Try standing outside when it is 100 degrees, and then go for it when it is 40. In the heat, just standing there you’ll begin to perspire, but that’s it. Sweating is merely the body’s mechanism for keeping you cool and at homeostasis, the tendency toward a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes (a wordy definition for your body’s perfect balance point where it is not working too hard to either keep you warmer, cooler, or near any other state. Now, back to the temperature experiment; if you stand outside when it is frigid, you will quite quickly recognize that you begin to shiver. Shivering, or shaking, is essentially many small muscle contractions at a high frequency. A muscle contraction requires a substantial amount of energy relative to sweating.
So, to make sense of the word problem I described up above, now imagine yourself making an effort outside, such as cycling. Riding a bike, you’re actually consuming energy above BMR (basal metabolic rate, or the amount of energy your body consumes at rest for an entire day). Because the caloric cost is greater when you’re exercising in the cold, you need to eat, and even drink, more than you would if you were riding in a nice, sunny, 70 degree climate like Southern California in March or April.
Luckily, the plan of action for fueling when it is chilly outside is really quite simple. You don’t need to eat anything different; you just need to eat more. And, I’m not trying to say that doubling up on the caloric intake per hour is the way to go, but aiming for around 50 more calories per hour than usual is a good goal. Try and make up the difference at other times throughout the day as well. Eating enough of the right foods at the right times will help keep you on the path to getting faster.