Eunice Newton Foote’s long-forgotten climate-science discovery.

Today, 11 February, is International Day of Women and Girls in Science, a perfect day to explore the long-overlooked but ground-breaking climate discovery of scientist Eunice Newton Foote.

Born as Eunice Newton on 17 July 1819 in Goshen, Connecticut, Foote was an American amateur scientist, inventor and women’s rights campaigner, but for far too long her contribution to climate science had been lost to history.

Foote was the first scientist to propose the connection between carbon dioxide and global warming by theorising that changing the concentration of CO₂ in the atmosphere would in turn change atmospheric temperature, and thus the climate. She did so three years before John Tyndall proved the physics behind the connection between atmospheric CO₂ and the greenhouse effect.

In 2010, retired petroleum geologist Ray Sorensen came across a summary of Foote’s work published in an 1857 volume of The Annual of Scientific Discovery. It detailed the presentation of her short paper, Circumstances Affecting the Heat of the Sun’s Rays, at the American Association for the Advancement of Science (AAAS) conference in 1856.

The experimental design and her findings

In her 1856 paper, Foote conducted experiments to address a scientific question previously posed to AAAS, regarding whether the heat of the Sun’s rays at the surface of the Earth were affected by the density of the air.

Explained in a short page and a half, her experiment used two glass tubes of the same size, in which she placed a thermometer to measure their temperatures. Filling the tubes with oxygen gas, dry or damp air, or carbonic acid gas (the term back then for carbon dioxide), she also used an air pump to remove the gas from one and to compress it within the other.

She then left the tubes either in full sun or in the shade and measured their temperature change over time, finding that the tubes containing water vapour (damp air) and CO₂ rose in temperature more than those containing normal air, and took much longer to cool back down.

“The highest effect of the sun’s rays I have found to be in the carbonic acid [CO₂] glass,” she wrote. “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.”

Although her experimental design did have many limitations, the results of her experiment allowed Foote to correctly infer the relationship between the concentration of CO₂ in the atmosphere and the temperature of the planet.  

“An atmosphere of that gas would give to our earth a high temperature,” she wrote, “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 own action as well as from increased weight must have necessarily resulted.”

When Foote carried out her experiment in the 1850s, CO₂ levels in the atmosphere were about 190 parts per million (ppm), meaning that for every million air particles, 190 of them were CO₂. Today, atmospheric CO₂ concentrations have climbed to record levels above 400 ppm.

Fourier, Foote and Tyndall

So, did she discover the greenhouse effect?

In the 1820s French mathematician and physicist Joseph Fourier calculated that, if only warmed by incoming solar radiation, the Earth should be much colder than it is. He thought the Earth’s atmosphere might act as a kind of insulator, which is widely recognised as the first proposal of what is now known as the greenhouse effect.

Foote was the first to understand that changing the amounts of certain gases in the atmosphere – such as carbon dioxide and water vapour – could change the temperature of the atmosphere and therefore the climate.

Her paper was published in the American Journal of Science and Arts in 1856. Joseph Henry of the Smithsonian Institute presented Foote’s paper instead of her, though since women were allowed to speak at AAAS conferences at the time, it is unknown why this was done.

Foote’s experiments were not sophisticated enough to isolate and detect the physics behind the greenhouse effect. In 1859, Irish physicist John Tyndall directly showed the physical basis behind the greenhouse effect by demonstrating that some gases – such as CO₂, methane and water vapour – absorb and radiate longwave infrared (thermal) radiation from the Earth’s surface.

Foote was not credited in his work, and it’s not known whether Tyndall knew about it.

It’s important to recognise Tyndall and Foote’s vastly different circumstances. While Foote had formal training in science, having studyied at the Troy Female Seminary and taken classes at the nearby men’s science college, she was an amateur scientist and a woman in a country without much scientific infrastructure. Tyndall had a doctorate from the University of Marburg, had worked with some of the greatest experimental physicists of the day, and had access to the latest equipment.

Campaigner for women’s rights

Foote wasn’t only a scientist; she was also a campaigner for women’s rights. She was present at the first Women’s Rights Convention in the United States in Seneca Falls, New York in 1848.

It was there that the Declaration of Sentiments – a document demanding equality in social status and legal rights for women (including the right to vote) – was presented. She was a signatory on the document written by prominent suffragist Elizabeth Cady Stanton, and was also one of the five women who prepared the proceedings of the convention for publication.

Foote was a distant relative of Isaac Newton and married Elisha Foote, a judge and mathematician. They had a daughter, Mary Foote, who became an artist and writer. Eunice died on 30 September 1888, aged 69 years, and was buried in Green-Wood Cemetery in Brooklyn, New York.

Even though Foote’s work went unrecognised in the scientific community for more than 150 years, the 2011 publication of Sorensen’s findings brought belated public recognition. A short film, Eunice, about her discovery and her fight to be taken seriously as a female scientist, was produced in 2018 and submitted to the year’s SCINEMA International Science Film Festival.