Where can I find a calorie burn calculator that also considers ambient temperature in the calculation?

You do realize those are estimates right? And there are bigger factors than ambient temperature differences unless you're working out in the Antarctic.

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let's try this..

let's ask.... "how many calories will you burn if you drink 1 gallon of ice water"

and of course, the ice water is at 0°C and your body warms it to.. say 37°C

answer.. .

1gal x (3.78L / gal) x (1000g / L) x (1cal/g°C) x (37°C-0°C) x (1Cal / 1000cal) = 37 dietary calories.

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now.. by single digits... I take it you mean °C single digits... like 9°C.. right?..

The actual additional Cal burned would depend on how much of you there was, what you were wearing for insulation, the speed at which you were riding, relative humidity, etc.. Too many variables to count.

but..

Even if we said 0°C.. and your internal body temp was 37°C, I'd expect the additional Calories burned to be in the single digits.