By all rights, Eunice Newton Foote should be a household name.

More than a century and a half ago, Foote was part of one of the most important scientific discoveries of our time: revealing the role of carbon dioxide in the earth’s greenhouse effect.

And yet relatively few people have heard of her.

Foote was the first person to demonstrate that carbon dioxide is a greenhouse gas, and also the first person to suggest that an atmosphere containing high levels of carbon dioxide would lead to a warmer earth.



Her research findings, contained in the paper “Circumstances affecting the heat of the sun’s rays,” were presented at the August 23, 1856, annual meeting of the American Association for the Advancement of Science. Being female, however, Foote was not allowed to read her own paper. Instead, Professor Joseph Henry of the Smithsonian Institution spoke on her behalf.

A few years later, Foote’s findings were reflected in the studies of physicist John Tyndall, whose research expanded on Foote’s discovery. And while Tyndall’s research is widely accepted as one of the foundations of modern climate science, Foote has faded to relative obscurity.

The morning of August 23, 1856, saw hundreds of men of science, inventors and curious persons gathered in Albany, New York, for the Eighth Annual Meeting of the American Association for the Advancement of Science, the largest attended to date. The annual meetings of the AAAS brought together scientists from around the United States to share groundbreaking new discoveries, discuss advancements in their fields and explore new areas of investigation. Yet this particular meeting failed to deliver any papers of quality—with one notable exception
That exception was a paper entitled “Circumstances affecting the heat of the sun’s rays,” by Eunice Foote. In two brisk pages, Foote’s paper anticipated the revolution in climate science by experimentally demonstrating the effects of the sun on certain gases and theorizing how those gases would interact with Earth’s atmosphere for the first time. In a column of the September 1856 issue of Scientific American titled “ Scientific Ladies,” Foote is praised for supporting her opinions with “practical experiments.” The writers noted: “this we are happy to say has been done by a lady.”

Foote’s paper demonstrated the interactions of the sun’s rays on different gases through a series of experiments using an air pump, four thermometers, and two glass cylinders. First, Foote placed two thermometers in each cylinder and, using the air pump, removed the air from one cylinder and condensed it in the other. Allowing both cylinders to reach the same temperature, she then placed the cylinders with their thermometers in the sun to measure temperature variance once heated and under various states of moisture. She repeated this process with hydrogen, common air and CO2, all heated after being exposed to the sun.

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.

Three years later, the well-known Irish physicist John Tyndall published similar results demonstrating the greenhouse effects of certain gases, including carbonic acid. Controversial though well recognized at the time, Tyndall theorized that Northern Europe was once covered in ice but gradually melted over time due to atmospheric changes. This laid the groundwork for how atmospheric variations over time in addition carbon dioxide emissions could have profound effects on global climate. Presently, Tyndall’s work is widely accepted as the foundation of modern climate science, while Foote’s remains in obscurity.

Why?

It goes without saying that the 19th century was not an easy era to be a woman and scientifically curious. With limited opportunities in higher education for women and the gate-keeping of scientific institutions like AAAS, which was all-male until 1850, science was largely a male-dominated field. Even the Smithsonian Institution, one of America’s premier scientific research institutions, was built on the clause “for the increase and diffusion of knowledge among men” (emphasis added). Born in 1819, this is the landscape that Foote found herself navigating.

Here are some key passages from her paper, “Circumstances Affecting the Heat of the Sun’s Rays”:

“The experiments were made with an air-pump and two cylindrical receivers of the same size, about four inches in diameter and third in length. In each were placed two thermometers. . . .”

After various experiments looking at the effect of filling the cylinders with high-pressure air, low-pressure air, humid air, and dry air, Foote filled one cylinder with carbon dioxide and the other with regular air. She placed each cylinder in the sun and watched the thermometers.

“The highest effect of the sun’s rays I have found to be in carbonic acid [i.e., carbon dioxide] gas.

“One of the receivers was filled with it, the other with common air, and the result was as follows . . . . The receiver containing the gas became itself much heated—very sensibly more so than the other—and on being removed, it was many times as long in cooling. . . . On comparing the sun’s heat in different gases, I found it to be in hydrogen gas, 104º [Fahrenheit]; in common air, 106º; in oxygen gas, 108º; and in carbonic acid gas, 125º.”

Foote recognized what her discovery meant for carbon dioxide’s power to affect the climate:

“An atmosphere of that gas [i.e., carbon dioxide] 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 as present, an increased temperature from its own action as well as from increased weight must have necessarily resulted.”

You can download the full paper as a PDF or see it in the original journal from the Internet Archive. You can cite the paper as:

Eunice Foote, “Circumstances Affecting the Heat of the Sun’s Rays,” The American Journal of Science and Arts 22, no. 46 (November 1856): 383–384.