The warming effect of sunlight on different gases was examined in 1856 by Eunice Newton Foote, who described her experiments using glass tubes exposed to sunlight. The warming effect of the sun was greater for compressed air than for an evacuated tube and greater for moist air than dry air. “Thirdly, the highest effect of the sun’s rays I have found to be in carbonic acid gas.” (carbon dioxide) She continued: “An atmosphere of that gas would give to our earth a high temperature; and if, as some suppose, at one period of its history, the air had mixed with it a larger proportion than at present, an increased temperature from its action, as well as from an increased weight, must have necessarily resulted.”

Looking back on Earth’s history, Foote explains that “an atmosphere of that gas would give to our earth a high temperature … at one period of its history the air had mixed with it a larger proportion than at present, an increased temperature from its own action as well as from increased weight must have necessarily resulted.” Of the gases tested, she concluded that carbonic acid trapped the most heat, having a final temperature of 125 °F. Foote was years ahead of her time. What she described and theorized was the gradual warming of the Earth’s atmosphere — what today we call the greenhouse effect.