It would appear, then, that man is really capable of exercising a certain control over the humidity of the climate, by thinning the forests, or by renewing them in the manner represented; nor can it be doubted, that the same effect will be brought about by drainage, which carries off the redundant waters into their appropriate channels, instead of allowing them to stagnate upon the surface.
And in thus altering the character of a country with respect to its humidity, he may hope to bring about a corresponding change also in its temperature, for the tendency of swamps and stagnant waters is to cool down by their evaporation the surface of the earth, as well as to intercept the rays of the sun by the mists and fogs they engender.
I'll buy that. It even sounds testable, go figure.
--From Climate: an inquiry into the causes of its differences...--