From Foote-Note to Climate Science Founder

This article, without commentary, first appeared in Physics Today.

Eunice Newton Foote’s nearly forgotten discovery

On 23 August 1856, Eunice Newton Foote sat in the audience at an American Association for the Advancement of Science (AAAS) meeting in Albany, New York, to attend a talk about her own work. She did not present her research. Instead, surrounded by America’s elite scientists, she listened as Joseph Henry, secretary of the Smithsonian Institution, presented—and failed to recognize the implications of—her research on the heat-absorbing properties of carbon dioxide and water vapor. The work had led Foote to conclude that increased carbon dioxide in the atmosphere would lead to global warming. “An atmosphere of that gas [carbon dioxide] would give to our earth a high temperature,” Foote declared in the subsequent paper describing her work.

Perhaps because of Henry’s missteps, perhaps because of her gender, Foote’s groundbreaking conclusions fell into obscurity. For a century and a half, the world has instead remembered John Tyndall, an Irish physicist, as the person who discovered the warming potential of carbon dioxide and water vapor—even though he published his findings three years after Foote.

It was not until 2011, when geologist Raymond Sorenson stumbled upon an account of Henry’s presentation of Foote’s work, that Foote began to receive her due. Sorenson immediately realized that Foote’s discovery and conclusion about carbon dioxide’s effect on climate predated Tyndall’s, generating new interest in her life and scientific work.

Suffragette and scientist

Eunice Newton was born in 1819 to Theriza Newton and Isaac Newton Jr, a distant relative of the famous mathematician and physicist. She grew up in Bloomfield, New York, and attended Troy Female Seminary, whose founder, Emma Willard, believed in educating young women in all subjects, including science. In 1841 Newton married judge, inventor, and scientist Elisha Foote. They briefly lived in Seneca Falls, where they were neighbors and friends of suffragette and abolitionist Elizabeth Cady Stanton. Both Footes were involved in the women’s rights movement; they attended the famed Seneca Falls Convention and signed the 1848 Declaration of Sentiments, a document protesting women’s disenfranchisement.

Never forgetting her childhood exposure to science, Eunice stayed up-to-date on current scientific literature. Her 1856 experiment was likely a response to a Scientific American volume that discussed theories about how the Sun heats Earth. A debate ensued on why mountaintops were colder than valleys. Some believed it was due to the angle of the Sun’s rays; others believed it came down to air density. Foote devised an experiment to settle that debate. Foote’s experiment was simple: She placed two identical thermometers in identical glass cylinders, 30 inches long and 4 inches in diameter. Using an air pump, she exhausted air from one cylinder and added air into the other. After the temperatures equalized, she placed the jars next to each other in the Sun and recorded the resulting temperature every two to three minutes. She also conducted the experiment with both jars in the shade. In comparing the temperature changes, she observed that “the [thermal] action increases with the density of the air, and is diminished as it becomes more rarified.” She repeated the experiment using moist and dry air by adding water to one cylinder and dehydrating the other using calcium chloride. She discovered that damp air became significantly hotter than dry air.

Last, she measured the effect of different gases against “common air” (the ambient atmosphere) and found “the highest effect of the sun’s rays . . . to be in carbonic acid gas.” She noted that after being removed from direct sunlight, carbon dioxide maintained its high temperature much longer than other gases did. She also tested hydrogen and oxygen but listed only their final temperature values. “What really struck me was the elegance of her experimental design,” particularly her careful attempt to reduce experimental errors through control groups, says Joseph Ortiz, a climate scientist who recently analyzed Foote’s research.

The penultimate paragraph of her short paper summarized her groundbreaking conclusion: Additional carbon dioxide in the atmosphere would cause global warming, “and if as some suppose, at one period of [Earth’s] 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.” Despite Foote’s impressive experiment and prophetic conclusion, she made no attempt to explain the mechanism by which the gases absorbed heat. It would have been difficult for her to do that because of the limitations of her experiment. She did not measure the pressure inside the apparatus, which would impact the temperature as she added various gases. Additionally, we now know the greenhouse effect is caused by infrared (IR) radiation, not visible light. It is unknown if the gases in her experiment were heated by direct sunlight or if the sunlight heated the glass, which in turn radiated in the IR within the jar. Likely it was a combination of various mechanisms. However, those limitations do not change the fact that Foote was the first to discover the heat-absorbing property of the gases and connect it to climate.

A groundbreaking conclusion overlooked

It remains unclear why Henry, a family friend and one of America’s leading physicists, and not Foote presented her findings on that August day in 1856. The attendees of the AAAS meeting, which included New York State officials and established scientists but notably few younger members, speak to the prestige of the event. The meeting was a friendly affair for some; it was “scarcely possible for a warmer or more hospitable welcome to be offered,” one attendee reported in the Canadian Journal of Industry, Science, and Art . But for a woman scientist, that probably was not the case. At the time newspaper reports of scientific meetings would remark on the beauty of the wives and daughters of attendees; one even mentioned a burlesque show held for one of the scientists. Though the AAAS constitution did not explicitly discriminate against women scientists, only a few were extended membership in the 19th century, and those who were members rarely presented their own work.

Henry’s talk was not mentioned in the official proceedings of the meeting. But in his remarks about Foote’s paper, which were reported in the New-York Daily Tribune , he discounted the importance of her findings. Henry reportedly stated “that although the experiments were interesting and valuable, there were [many] [difficulties] encompassing [any] attempt to interpret their significance.”

Foote’s work was not widely publicized after the meeting either. Her paper, titled “Circumstances affecting the heat of the sun’s rays ,” was printed in the American Journal of Science and Arts next to an article published by her husband. It did get noticed in an 1856 Scientific American article, “Scientific ladies.—experiments with condensed gases ,” that contextualized her research as part of the larger body of work dedicated to understanding the climate of the geologic past. The unnamed author also praised the work of women scientists and stated that “the experiments of Mrs. Foot[e] afford abundant evidence of the ability of women to investigate any subject with originality and precision.”

Brief summaries of Foote’s paper appeared in two European publications, one of which miscredited the work to her husband, and neither of which mentioned the paper’s climate conclusion. Henry’s presentation of her work was also covered by the Canadian Journal of Industry, Science, and Art as well as by David A. Wells in his Annual of Scientific Discovery. Wells even mentioned Foote’s research in future publications, but without citation—despite rigorously citing other scientists whose work he referenced, all of whom were men.

Foote’s words had made it to the international scientific stage, but it seems no one was listening. Her discovery was not mentioned again.

What did Tyndall know?

By 1859, when John Tyndall published his preliminary results on the greenhouse effect of carbon dioxide, water vapor, and methane, he was already a well-connected and respected physicist. After observing how altitude affects temperature while spending time in the Swiss Alps, Tyndall conducted an experiment to test how different gases respond to heat. He referred to the contemporary literature on heat by Horace Bénédict de Saussure, Joseph Fourier, Claude Pouillet, and William Hopkins as the basis for his work and was interested in exploring the nature of the interaction of molecules with thermal radiation.

Because of his reputation and connections, Tyndall was able to use state-of-the-art, custom equipment for his experiment. He used “radiant heat,” today known as IR radiation, and a differential spectrometer to obtain high-precision data. When he first measured oxygen, hydrogen, and nitrogen, none showed significant signs of heat absorption. He then measured other atmospheric gases, including water vapor and carbon dioxide, and came to the same conclusion as Foote that both gases contribute to atmospheric heating. In addition, he explicitly attributed the radiant heat of Earth’s surface as the cause for the heating, which is now known as the greenhouse effect. Realizing the importance of his results, he rushed to report his preliminary findings in 1859 and published his full paper, “On the absorption and radiation of heat by gases and vapours, and on the physical connexion of radiation, absorption, and conduction ,” in 1861.

Historians disagree on whether Tyndall knew of Foote’s work. Not only was Tyndall a well-informed physicist who would likely be interested in reading the literature on topics he was exploring, but he was on the editorial board of Philosophical Magazine. The publication reprinted the paper by Foote’s husband that was directly next to hers in the American Journal of Science and Arts, though that paper had less significant results. Someone at the Philosophical Magazine saw her work and chose not to publish it, and it seems plausible that Tyndall could have been exposed to her paper through his position on the editorial board.

Nonetheless, there is no evidence that Tyndall read Foote’s paper. He makes no mention of her work in any correspondence. He even performed his experiment in a way that indicated he did not know her conclusions. If he was aware that water vapor and carbon dioxide would absorb heat, it is likely he would have tested those first. Instead, he started with gases like oxygen and hydrogen, which Foote explicitly mentioned did not display any significant heat-absorbing properties, and seemed surprised by his results. Roland Jackson, who wrote a biography of Tyndall, concluded in a 2019 paper that it is unlikely Tyndall knew of Foote’s work. Tyndall “thought of himself as an upright moral character,” Jackson says. “He defended people he thought had been overlooked. [He was] not someone who would purposefully plagiarize.”

Tyndall’s paper was celebrated as a scientific breakthrough and quickly became part of the climate science canon. Lord Kelvin remarked that the findings were novel, suggesting he, too, did not know of Foote’s work. Jackson notes that even mathematical physicist Peter Guthrie Tait, “an absolute sworn enemy of Tyndall,” never brought up Foote’s work. “If he had thought that Tyndall had essentially stolen Foote’s work,” says Jackson, Tait “would have gone to town.” It is possible that readers saw Foote’s name and skipped over her paper because of her gender. Perhaps European bias came into play as well. Much like the country itself, the scientific infrastructure in the US was relatively new, and many European scientists looked down on the work of American scientists, Jackson says. Though those explanations are reasonable, it is still a puzzling oversight. “The whole thing is most curious,” Jackson says. “I cannot explain why nobody, including Henry, knew of the significance of Foote’s work. I don’t think it is just because she is a woman or an amateur. If you look at the Scientific American article, [the author] recognized the work was interesting, and still nobody picked up on it.”

Remembering Foote and her impact

[This section was edited to clarify that Foote presented her second article at a AAAS meeting]

Foote published one more paper, in 1857, “On a new source of electrical excitation ,” in which she measured the static electricity of different conditions. This time, she presented her own paper for AAAS. Once that work was complete, she returned to campaigning for women’s suffrage and did not publish in a scientific journal again. Instead, her scientific contributions continued in the form of inventions. She has three patents in her name, and it is suspected she assisted her husband in some of his inventions. She died in 1888.

Foote’s daughters, Mary and Augusta, also left their mark. Mary Foote Henderson was a social activist, author, and real-estate developer. She married John B. Henderson, the US senator who introduced to Congress the Thirteenth Amendment abolishing slavery. Augusta Foote Arnold was an author and a trustee of Barnard College. She wrote cookbooks and shared her parents’ interest in science, publishing The Sea Beach at Ebb Tide: A Guide to the Study of the Seaweeds and the Lower Animal Life Found Between Tide-Marks under the pen name Mary Ronald.

In the years following Foote’s resurfacing in 2011, historians and climate scientists started digging to find more information about the woman who predicted climate change, but the work was difficult. Some articles and books that referenced her research did not cite her name, and there is no known image of her. Liz Foote, a PhD candidate studying environmental science and behavioral science and a distant relative of Elisha Foote, learned about Eunice Foote only accidentally, while watching a keynote address by climate scientist Katharine Hayhoe at a 2018 AAAS meeting. Foote recognized her name, dug into her family history, found her connection, and joined the search for an image.

Ortiz and Jackson teamed up to study Foote after a Twitter correspondence spurred by a tweet by climate scientist Sarah Myhre. They gleaned as much information from primary sources as possible and published their analysis last year.

Foote’s story is important for many reasons. Amid an overwhelming number of floods, heat waves, and wildfires, the effects of human-caused climate change have never been so apparent . In 1856 Eunice Newton Foote was able to conclude that increasing carbon dioxide levels in Earth’s atmosphere would cause warming. She did not mean for it to be a warning, but perhaps, in the midst of America’s industrial revolution, it should have been. “Scientists have known for a long time that humans impact climate,” Ortiz says. Foote’s words are a reminder that the notion of global warming has been in scientific circles for more than 150 years.

Perhaps more poignant, Foote’s fall into obscurity is part of a larger narrative of women’s disenfranchisement in the scientific establishment. It might not be a coincidence that Foote was fighting for women’s voices to be heard by the government while hers was being overlooked by the scientific community. Says Liz Foote: “From what I know about Eunice’s life, she benefited from a great deal of privilege. . . . But as a woman in the 1800s her professional options were nevertheless limited. To accomplish what she did, despite the realities of her time, is very impressive and should inspire anyone.”