There is also the mathematics of exponential functions.

If F = X^Y (^means exponent)

and both X and Y are greater than 1, a 10% change in X or Y or both results in a much bigger change in F.

The scientists are using these exponential functions a lot in their models. Even if they were to get a good handle on X or Y, nature is probably going to give them a value +/ — 20%.