One of many, and one of the best. Unless you performed the scientific method yourself or closely watched someone perform it, it's not available to you and you have to use another. A truthful-seeming report of someone else performing it is pretty far up the ladder, until the enemies learn to write false experiment reports indistinguishable from real ones.

Not all fields of study are amenable to the scientific method, and lesser scientific methods are the best possible. We can't duplicate earth and flood one with CO2. We have to reach farther down the heuristic ladder, like studying two glass bottles, one filled with CO2. This can be extrapolated to calculate what a planet filled with CO2 would do, but the maths required is much less accessible.