How long have we known that human-driven climate change could be a catastrophe?

In the last few decades, there have been plenty of modern warnings. Perhaps the most famous was in 1988, when James Hansen—then a NASA scientist—told Congress “the evidence is pretty strong that the greenhouse effect is here.” Since then, the consensus from scientists has only increased, and polls show that 3 in 4 Americans agree that human activity is warming the climate, not least because the ravages are already here, with Key Largo neighborhoods underwater and California wildfires raging. There’s arguably never been as much public attention to the existential problem of runaway greenhouse gases.

But the road to understanding climate change stretches back to the tweed-clad middle years of the 19th century—when Victorian-era scientists conducted the first experiments proving that runaway CO2 could, one day, cook the planet.

In other words, “global warming was officially discovered more than 100 years ago.”

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Early climate research grew out of the astonishing ferment of science in that century. Scientists were formulating the basis of our modern understanding of thermodynamics, and its connection to chemistry and molecular physics. One was Joseph Fourier, a French mathematician and physicist who spent his career pondering the mechanics and equations governing heat transfer. He was intrigued by a puzzle: Why was the Earth as warm as it was? When he estimated how much energy from the sun hit our planet, he figured the Earth ought to be colder than it is.

The answer, he proposed, must be the atmosphere: It was somehow preventing heat from escaping. In an 1824 paper, he hypothesized that gases in the atmosphere must create barriers that acted to trap heat. Fourier didn’t yet know what molecular mechanisms were trapping the heat. But in an 1837 paper for The American Journal of Science and Arts, he surmised that over a long period of time, the amount of heat held in by the atmosphere could change — altered by both the Earth’s natural evolution and human activity. “The establishment and progress of human society, and the action of natural powers, may, in extensive regions, produce remarkable changes in the state of the surface, the distribution of the waters, and the great movements of the air,” he predicted. “Such effects, in the course of some centuries, must produce variations in the mean temperature for such places.”

It was one of the first predictions that climate change could occur—though it wasn’t clear quite how or why it would happen. What precise gases could have such an effect?

“An atmosphere of that gas,” Eunice Newton Foote noted, “would give to our earth a high temperature.”

The answer began to emerge in 1856, when the results of a remarkable experiment were unveiled. Eunice Newton Foote, an amateur scientist and prominent suffragette, for the first time tested the heat-trapping abilities of different gases. She took several glass cylinders, put a thermometer in the bottom, and then filled them with gas combinations ranging from very thin air to thicker air, humid air, and air with “carbonic acid,” or what we now call CO2. Foote placed the cylinders in the sun to heat up, then in the shade to cool down. When she observed how the temperatures changed, she found that the cylinder with CO2 and water vapor became hotter than regular air, and retained its heat longer in the shade. In other words, wet air and CO2 were heat-trapping gases.

When she wrote up her experiment for an 1856 issue of The American Journal of Science, Foote made an eerily prophetic observation: What happened inside the CO2 jar could also happen to our planet. “An atmosphere of that gas,” she noted, “would give to our earth a high temperature.”

Foote had launched the first true experimental work in climate physics, but, tragically, it was lost to history. When time came to present her research before the American Association for the Advancement of Science—among the country’s most eminent scientific gatherings—they didn’t allow women to speak, so it was read by a male colleague. Climate scientists for more than a century, clustered in the early decades primarily in Europe, did not appear to discuss or cite Foote’s work. “She had three strikes against her,” as John Perlin, a researcher at the University of California in Santa Barbara notes. “She was female. She was an amateur. And she was an American.” Her work only resurfaced in the last decade, as papers uncovering it emerged.

Instead, the climate-science spotlight was quickly grabbed by the Irish scientist John Tyndall. He was a wide-ranging researcher with a knack for building precision experimental equipment (and for discrediting the hot trend for seances and communicating with the spirit world). Tyndall was also consumed with a question that loomed large in Victorian science: What had caused the world’s previous ice ages? Geologists had been uncovering evidence that suggested the earth had, at various points in the past, been covered by mammoth amounts of ice. It was an exciting discovery, but it wasn’t clear precisely why the planet’s temperature had fluctuated so wildly.

One theory followed Fourier’s line of reasoning, and argued the composition of the atmosphere was the culprit. If it changed, it could begin holding—or losing—significant amounts of heat. Tyndall thought this was the most plausible answer, and in 1859 wanted to figure out which gases were the heat-trappers.

(This was, of course, precisely the same thing Foote had explored only three years previously! But in Tyndall’s later writings, he claims he’d never heard of her. This presents historians with a murky question: Was Tyndall telling the truth? Or had he ripped off Foote’s work and intentionally cut her out of any mention in his work? There’s some debate about that. Some think he deliberately omitted mentioning her experiments when he wrote up his own. Others argue that he was simply unaware of her paper, and that if he had known of it, he’d have designed a more efficient set of experiments for his own explorations.)

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Either way, between 1859 and 1860, Tyndall created some ingenious precision equipment to test gases. He crafted a long tube of glass, and heated up one end via devices ranging from a hot cube of metal to boiling water. He put various gases inside the tube, sealing them in with rock salt, and then measured how much heat could travel through the gas. Much like Foote, he found that water vapor and CO2 were remarkably powerful at trapping heat: Indeed, CO2 could trap 1,000 times as much as dry air.

The results stunned him, as he later explained in an 1861 lecture describing the results. As he noted, science hitherto had assumed that colorless gases like CO2 allowed heat to slide easily past. “Those who, like myself, have been taught to regard transparent gases as almost perfectly diathermanous (transparent to heat), will probably share the astonishment with which I witnessed the foregoing effects,” he said. In fact, the power of CO2 was so baffling that he repeated the experiment hundreds of times to make sure the results were solid. Tyndall was probably experiencing the incredulous reaction that many laypeople still feel today, as they ponder how such tiny amounts of CO2—a few hundred parts per million—could so alter the planet.

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The final advance in climate science arrived in 1896, when the Swedish physicist Svante Arrhenius created what was, in effect, the first model of climate change.

Arrhenius was, like Tyndall, was mostly interested in settling the debate about ice ages. The fight had produced several competing explanations. One argued that ice ages were caused by perturbations in Earth’s orbit; Arrhenius didn’t think that was plausible. Another theory chalked it up to changes in the atmosphere, including CO2, which made much more sense to Arrhenius. So what he wanted to calculate was how much CO2 it would take to alter global temperatures.

Thankfully, he had some interesting recent data to work with. A Swedish scientist, the geologist Arvid Högbom, had recently published an essay estimating how much CO2 existed on the planet throughout history. Another researcher, Samuel Pierpont Langley, had also recently invented a highly precise thermal detector that he used to measure how much energy the atmosphere allows through, and inhibits from leaving. Armed with that info, Arrhenius began calculating how much heat would be trapped if levels of CO2 and water vapor—“selective absorbers,” as he called them—changed.

Arrhenius reached “a conclusion that millions of dollars worth of research over the ensuing century hardly changed at all.”

It was a grind. Arrhenius, as the historian Elisabeth Crawford writes, had to perform by hand “calculations estimated to have been between 10,000 and 100,000.” He spent all of 1895 hunched over his figures, and Arrhenius himself complained loudly about the “tedious” work to friends in letters, at one point miserably noting how it was “unbelievable that so trifling a matter has cost me a full year”.

When he was done, he made a striking prediction: If you doubled the amount of CO2 in the atmosphere, it would raise the world’s temperature by 5 to 6 degrees Celsius. Remarkably, that analysis holds up pretty well today, even in an age where climate analysis involves far more information and variables and are crunched by cloud supercomputers. Despite having done his work by hand, using data that even he regarded as woefully inadequate, Arrhenius reached “a conclusion that millions of dollars worth of research over the ensuing century hardly changed at all,” as Isabel Hilton wrote in 2008. The era of modern climate modeling was born.

Nonetheless, Arrhenius and his peers did not actually worry about global warming, or fret about industrialization cooking the planet. Certainly, the industrial revolution was well underway, burning oodles of coal. But the scientists didn’t imagine the consumption of fossil fuels could ever become huge enough to seriously alter the planet. They couldn’t imagine what then next century would bring, with millions of automobiles on the road, coal-burning plants pumping out electricity, and deforestation ravaging the world’s carbon-sinks. So Arrhenius predicted that climate change would happen, sure, but awfully slowly: He expected it would take 3,000 years—fully 30 centuries—for CO2 levels in the atmosphere rise by 50%. Instead, we shot up by 30% in only one century.

When it came to disaster, he and his peers were rather more concerned by the possibility of volcanic eruptions disrupting the climate. Only a few years earlier, the island of Krakatoa had exploded in a volcanic fury, dumping so much sulphur dioxide into the sky that it cooled the Northern hemisphere for over a year and killed thousands. They understood that the lethal danger of sudden climate change. But they couldn’t imagine the dangers of gradual heating. To be sure, the burning of so much coal seemed like a problem, because even back then people knew fossil fuels weren’t renewable. What would happen when they’re gone?, pondered pundits of the day. But they didn’t foresee the far more wicked problems that a warming climate would bring—the challenges of migrating invasive species, say, or the complex feedback loops that emerge as glaciers vanish.

Actually, Arrhenius thought a warmer world would have big upsides. In his 1908 book Worlds in the Making (which was primarily about Arrhenius’ passion for panspermism, the theory that life arrived on Earth via bacteria transported by solar winds), he wrote:

We often hear lamentations that the coal stored up in the earth is wasted by the present generation without any thought of the future, and we are terrified by the awful destruction of life and property which has followed the volcanic eruptions of our days. We may find a kind of consolation in the consideration that here, as in every other case, there is good mixed with the evil. By the influence of the increasing percentage of carbonic acid in the atmosphere, we may hope to enjoy ages with more equable and better climates, especially as regards the colder regions of the earth, ages when the earth will bring forth much more abundant crops than at present, for the benefit of rapidly propagating mankind.

It was a nice idea at the time—but nature, as is now dangerously clear, had different ideas. We’re now faced with the challenge of mitigating as much climate change as possible, while adapting to what’s already set in place. The onset of a warmer planet can seem sudden, if you judge by today’s panicked headlines. But the science predicting that it would occur? It is, alas, generations’ old.