Believe it or not, a respected physicist reported the first calculations linking humans to global warming way back in 1932 (via treehugger).
Turns out, E. O. Hulburt, who was the very first director of the Naval Research Laboratory and is the namesake of the Hulburt Center for Space Research, published a piece on this in the July 1932 issue of Modern Mechanics magazine.
Here's the quote:
Hulburt "found conclusive mathematical evidence that the earth's temperature is being warmed by the increased amount of carbon dioxide present in the air. Smoke stacks emit huge volumes of this gas, which is also found in the breath and waste products of humans and animals."
Further digging reveals a story from the '50s that does a marvelous job of explaining the problem, a "growing blanket of carbon dioxide" and even goes as far to present some fairly accurate predictions based on research by a professor at Johns Hopkins.