The History of the Greenhouse Effect
An early science history from the 1800s through 1963
Revised and adapted from ‘The Discovery of Global Warming’, Spencer Weart (2008)
Origins of the Theory of the Greenhouse Effect
Early in the 1800s, the French scientist Joseph Fourier had asked himself a question. It was a deceptively simple question, of a sort that physics theory was just then beginning to learn how to address: what determines the average temperature of a planet like the Earth? When light from the Sun strikes the Earth’s surface and warms it up, why doesn’t the planet keep heating up until it is as hot as the Sun itself? Fourier’s answer was that the heated surface emits invisible ‘dark radiation’ (what we now call ‘infrared radiation’), which carries the heat energy away into space. If that was so, then why doesn’t Earth cool itself down all the way to the cold temperature of outer space?
The reason, Fourier intuited, was due to the Earth’s atmosphere, which somehow keeps some of the heat radiation in. He tried to explain this by comparing the Earth with its covering of air to a box covered with a pane of glass. The box’s interior warms up when sunlight enters and the heat cannot escape. The explanation sounded plausible, and several decades after Fourier's time, a few scientists had begun to speak of a ‘greenhouse effect’ that keeps the Earth from freezing. Though in fact it is a misnomer, for real greenhouses stay warm for other reasons (the main effect of the glass is to keep the air, heated by sun-warmed surfaces, from wafting away). As Fourier recognized, the way the atmosphere holds in heat on the entire Earth is more subtle. The atmosphere’s trick is to intercept a part of the infrared radiation emitted from the surface, preventing it from escaping into space. Jean-Baptiste Joseph Fourier, ‘On the Temperatures of the Terrestrial Sphere and Interplanetary Space’ (1824).
The correct reasoning for how Earth is kept warm was first explained lucidly by a British scientist, John Tyndall. Tyndall pondered how the atmosphere might control the earth’s temperature, but he was stymied by the opinion, held by most scientists at the time, that all gases are transparent to infrared radiation. In 1859 he decided to check this in his laboratory. He confirmed that the main gases in the atmosphere, oxygen and nitrogen, are indeed transparent. He was ready to quit when he thought to try coal gas. This gas, produced by heating coal and used for lighting, was piped into his laboratory. He found that for heat rays, the gas was as opaque as a plank of wood. Tyndall went on to try other gases, and he found that the gas
A bit of
Tyndall’s interest in all this had begun in a wholly different type of science. He hoped to solve a puzzle that was exciting great controversy among the scientists of his day: the prehistoric ice age. The claims were incredible, yet the evidence was clear. The scraped-down rock beds, the bizarre deposits of gravel found all around northern Europe and the northern United States—these looked exactly like the effects of Alpine glaciers, only immensely larger. Amid fierce debate, scientists were coming to accept an astounding discovery. Long ago—although not so long as geological time went, for Stone Age humans had lived through it—northern regions had been buried kilometers deep in continental sheets of ice. What could have caused this?
Changes in the atmosphere were one possibility, although not a promising one. Of the atmospheric gases,
The riddle of the ice age was taken up in 1896 by a scientist in Stockholm, Svante Arrhenius. Suppose, he said, the amount of
‘Cooling that causes less water vapor in the air that causes more cooling’ this is the kind of self-reinforcing cycle that today we call a ‘positive feedback’. The concept was both elementary and subtle—easy to grasp, but only after somebody pointed it out. In Arrhenius’s day only a few insightful scientists noticed that such effects could be crucial for understanding climate. The first important example had been worked out in the 1870s by a British geologist, James Croll, as he pondered possible causes of the ice age. When snow and ice had covered a region, he noted, they would reflect most of the sunlight back into space. Bare, dark soil and trees would be warmed by the Sun, but a snowy region would tend to remain cool. Once something started an ice age, the pattern could become self-sustaining.
Such complex effects were far beyond anyone’s ability to calculate at that time. The most Arrhenius could do was to estimate the immediate effects of changing the level of
Were such large changes in atmospheric composition possible? For that question Arrhenius turned to a colleague, Arvid Högbom. Högbom had compiled estimates for how
The idea of humans massively perturbing the atmosphere did not trouble Arrhenius. It was not just that warming seemed a good thing in chilly Sweden. Arrhenius, like nearly everyone at the end of the nineteenth century, expected any technological change would be for the best. Many people believed that scientists and engineers would solve all major problems in the centuries to come. In any case, Arrhenius figured it would take a couple of thousand years to double the amount of
Scientific Skepticism of the Greenhouse Effect of CO2
Even as abstract theory, there were scientific reasons to dismiss Arrhenius’s idea. Most telling was a simple laboratory measurement made by another Swedish scientist, Knut Ångström (son of the more famous physicist Anders Ångström), that seemed to refute the entire principle of greenhouse warming. Ångström sent infrared radiation through a tube filled with
To kill any lingering doubts, other scientists pointed out a still more fundamental objection. They held that it was impossible for
Furthermore, scientists saw that Arrhenius had grossly oversimplified the climate system in his calculations. For example, with more water vapor held in the air as the Earth got warmer, surely the moisture would make more clouds. The clouds would reflect sunlight back into space before the energy ever reached the surface, and so the Earth should hardly warm up after all.
These objections conformed to a view of the natural world that was so widespread that most people thought of it as plain common sense. In this view, the way cloudiness rose or fell to stabilize temperature and the way the oceans maintained a fixed level of gases in the atmosphere were examples of a universal principle: the Balance of Nature. Hardly anyone imagined that human actions, so small among the vast natural powers, could upset the balance that governed the planet as a whole. This view of Nature—suprahuman, benevolent, and inherently stable—lay deep in most human cultures. It was traditionally tied up with a belief in the fundamental stability and order of the universe, a flawless and imperturbable harmony. Such was the public belief, and scientists are members of the public, sharing most of the assumptions of their culture. Once scientists found plausible arguments explaining how the atmosphere and climate would remain unchanged within a human timescale—just as everyone expected—they stopped looking for possible counter-arguments.
Of course, everyone knew climate could vary. From the old folks’ tales of the great blizzards of their childhood to the devastating Dust Bowl drought of the 1930s, ideas about climate included a dose of catastrophe. But a catastrophe was (by definition) something transient; things revert to normal after a few years. A few scientists speculated about greater climate shifts. For example, had a waning of rainfall over centuries caused the downfall of ancient Near Eastern civilizations? Most doubted it. And if such changes really did happen, everyone assumed they randomly struck one region or another, not the entire planet.
To be sure, many knew there had been vast global climate changes in the distant past. Geologists were mapping out the ice age—or rather, ice ages. For it turned out that the tremendous sheets of ice had ground halfway down America and Europe and back not once, but over and over again. Looking still further in the past, geologists found a tropical age when dinosaurs basked in regions that were now Arctic. A popular theory suggested that the dinosaurs had perished when the Earth cooled over millions of years. The most recent ice age likewise had come to a gradual end, geologists reported, as the Earth returned to its present temperature over tens of thousands of years. If a new ice age was coming, it should take as long to arrive.
Ideals of consistency pervaded not only the study of climate, but also the careers of those who studied it. Through the first half of the twentieth century, climate science was a sleepy backwater. People who called themselves ‘climatologists’ were mostly bookkeepers who kept track of average seasonal temperatures, rainfall, and the like. Typical were the workers at the U.S. Weather Bureau, ‘the stuffiest outfit you’ve ever seen’, as one of a later generation of research-oriented geophysicists put it. Athelstan Spilhaus, interview by Ron Doel, Nov. 1989, American Institute of Physics, College Park, Md. Their job was to compile statistics on past weather, in order to advise farmers what crops to grow or tell engineers how great a flood was likely over the lifetime of a bridge. These climatologists’ products were highly appreciated by their customers (such studies continue to this day). And their tedious, painstaking style of scientific work would turn out to be indispensable for studies of climate change. Yet the value of this kind of climatology to society was based on the conviction that statistics of the previous half century or so could reliably describe conditions for many decades ahead. Textbooks started out by describing the term climate as a set of weather data averaged over temporary ups and downs. Climate was stable by definition.
Greenhouse Theory Restored
Nobody advised Gilbert Plass to study greenhouse warming. In the 1950s the Office of Naval Research supported his work of theoretical calculations for an experimental group at Johns Hopkins University that was studying infrared radiation. As Plass later recalled, he got curious about climate change only because he read broadly about topics in pure science. He happened on the discredited theory that the ice ages could be explained by changes in
Plass knew the old objection to the greenhouse theory of climate change: in the parts of the spectrum where infrared absorption took place, the
Plass could say nothing more specific without extensive computations. Fortunately, he had access to newly invented digital computers. His lengthy calculations demonstrated that adding or subtracting some
Plass’s computation was too crude to convince other scientists, for he had left out crucial factors such as possible changes in water vapor and clouds. But he did prove a central point: the greenhouse effect could not be dismissed with the old argument that adding more
Geochemistry, the Ocean, and the Carbon Cycle
Another question was whether the level of
It happened that the movements of carbon could now be tracked with a new tool, radiocarbon—a radioactive isotope, carbon-14. Such isotopes were studied during the wartime work to build nuclear weapons, and the pace had not slackened in the postwar years. Sensitive instruments were developed to detect radioactive fallout from Soviet nuclear tests, and a few scientists turned the devices to measuring radiocarbon. Their studies also drew support from interests far removed from the Cold War. Archeologists were fascinated by the way radiocarbon measurements could give exact dates for ancient relics such as mummies or cave bones. The carbon-14 isotope is created in the upper atmosphere, when cosmic-ray particles from outer space strike nitrogen atoms and transform them into radioactive carbon. Some of the radiocarbon finds its way into living creatures. After a creature’s death, carbon-14 slowly decays at a fixed rate over hundreds and thousands of years to the stable nitrogen-14. Thus, the less of it that remains in an object, in proportion to normal carbon (carbon-12), the older the object is.
One of the new radiocarbon experts, the chemist Hans Suess, thought of applying the technique to the study of geochemistry. It occurred to him that the carbon emitted when humans burned fossil coal and oil is ancient indeed, its radioactive carbon-14 nearly all gone. He gathered wood from century-old trees and compared it with modern samples. In 1955 Suess announced that he had detected that ancient carbon (with depleted carbon-14 levels) had been added to the modern atmosphere, presumably from the burning of fossil fuels. But he thought that the fossil fuel carbon made up barely 1 percent of all the carbon in the atmosphere—a figure so low that he concluded that most of the carbon derived from fossil fuels was being promptly taken up by the oceans. A decade would pass before he managed to get more accurate measurements, which would show a far higher fraction of fossil carbon.
Everyone knew that radiocarbon measurements were tricky; Suess’s data were obviously preliminary and uncertain. The important thing he had demonstrated was that fossil carbon had shown up in the atmosphere. With more work one might figure out exactly how long it would take the oceans to absorb the carbon derived from burning fossil fuels. The question was intriguing, for as an oceanographer admitted, ‘Nobody knows whether it takes a hundred years or ten thousand.’ Roger Revelle, ‘The Oceans and the Earth,’ talk given at American Association for the Advancement of Sciences symposium, 27 Dec. 1955.
This oceanographer was Roger Revelle, a dynamo of a researcher and administrator who was driving the expansion of the Scripps Institution of Oceanography near San Diego, California. Sitting on a dramatic cliff overlooking the Pacific, the prewar Scripps had been a typical oceanographic establishment, quiet and isolated, with its small clique of a dozen or so gossiping researchers and a single research ship. It relied on private patronage, which faltered when the Depression bit into the Scripps family’s funds. The postwar Scripps was growing into something quite different, a complex of modern laboratories. Revelle won funding for a variety of projects under contracts from the Office of Naval Research, the natural patron for any research related to the oceans. One of Revelle’s many good ideas was to use some of the money to hire Suess to come to Scripps and pursue radiocarbon studies. By December 1955 the two had joined forces, combining their expertise to study carbon in the oceans.
From measurements of radiocarbon in seawater and air, Suess and Revelle deduced that the ocean surface waters took up a typical molecule of
The only question left, it seemed, was whether it would accumulate near the surface, or whether currents would carry it deep into the oceans. Revelle’s group was already studying the question of how fast the ocean surface waters turned over. It was a matter of national interest, for the navy and the U.S. Atomic Energy Commission were concerned about the fate of nuclear fallout from bomb tests. The Japanese were in an uproar over contamination of the fish they relied on. Moreover, if the ocean currents were slow enough, radioactive waste from nuclear power plants could be dumped on the ocean floor. Measurements of radiocarbon at various depths and other studies, pursued at Scripps and elsewhere in the 1950s, showed that on average the ocean waters turn over completely in several hundred years. That seemed fast enough to sweep the
But the ocean is not just salt water, but a complex mix of chemicals, so it was not obvious that seawater could actually hold on to the
It was now 1957, and Revelle and Suess were ready to send off for publication their paper describing how the oceans would promptly absorb all the extra
That reassuring conclusion was a gross underestimate. Revelle was assuming that industrial emissions during the coming centuries would continue at the 1957 rate. Scarcely anyone had yet understood that both population and industrialization were exploding in exponential growth. Between the start of the twentieth century and its end, the world’s population would quadruple, and the use of energy by an average person would quadruple, making a sixteen-fold increase in the rate of emission of
Different ideas were beginning to stir. The geochemist Harrison Brown was sketching out a vision of a future with exploding population and industrialization. Revelle had heard these ideas, and before he sent off for publication the paper he had written with Suess, he added a remark: the accumulation of
Revelle meant ‘experiment’ in the traditional scientific sense, a nice opportunity for the study of a geophysical process. Yet he did recognize that there might be some future risk. Other scientists too began to feel a mild concern as they gradually assimilated the meaning of Plass’s and Revelle’s difficult calculations. Adding
Revelle and Suess, like Arrhenius, Plass, and everyone else who up till then had made a contribution toward the discovery of global warming, had taken up the question as a side issue. They saw in it a chance for a few publications, a detour from their main professional work, to which they soon returned. If just one of these men had been possessed by a little less curiosity, or a little less dedication to laborious thinking and calculation, decades more might have passed before the possibility of global warming was noticed. It was also a historical accident that military agencies were scattering money with a fairly free hand in the 1950s. Without the Cold War there would have been little funding for research on a subject nobody had connected with practical affairs. The U.S. Navy had bought an answer to a question it had never thought to ask.
Revelle and Suess were now eager to learn more about the ‘large scale geophysical experiment’ of greenhouse warming. Few others paid much attention to their difficult technical paper. Government agencies like the navy could hardly be expected to devote much more money to a question that seemed unlikely to yield anything useful, or even more scientific information, without great effort. Fortunately, just then another purse opened up. The new funds came (or seemed to come) from peaceful internationalism, altogether apart from national military drives.
Measuring Atmospheric CO2
After the Second World War, governments saw new reasons to support international cooperation in science. This was the era that saw the creation of the United Nations, the Bretton Woods financial institutions, and many other multilateral efforts. The aim was to bind peoples together with interests that transcended the self-serving nationalism. In the mid-1950s a small band of scientists worked out a scheme to boost cooperation among the various geophysics disciplines. They hoped to coordinate data gathering on an international scale and—no less important—to persuade governments to add an extra billion or so dollars to their funding of geophysics research, thereby allowing for the hiring of more scientist researchers and funding for more experiments. Their plans culminated in the creation of the International Geophysical Year (IGY) of 1957–1958. The IGY would draw together scientists from many nations and a dozen different disciplines, to interact in committees that would plan and carry out interdisciplinary research projects grander than any attempted before.
Climate change ranked low on the list of IGY priorities. But with such a big sum of new money, there was bound to be something for climate-related topics. In the committees that allocated the U.S. share of funding, Revelle and Suess argued for a modest program to measure the gas in the ocean and air simultaneously at various points around the globe. It wouldn’t cost much, so the committee granted some money.
Revelle had David Keeling in mind for this work. Keeling was a young geochemist interested in understanding the processes that affect the level of
Keeling thought he could do better than that. The greatest accuracy called for expensive new instruments, far more precise than most experts thought were necessary to measure something that fluctuated as widely as
Keeling’s costly equipment, together with his relentless pursuit of every possible source of error, paid off. In Antarctica, he tracked down variations in the
But the IGY was winding down. By November 1958 the remaining funds had fallen so low that

Although some scientists immediately recognized the importance of Keeling’s work, no agency felt responsible for funding a climate study that might run for many years. In 1963 the work almost had to shut down. Keeling turned to the National Science Foundation, a U.S. federal agency established back in 1950 on a modest budget. The 1957 launching of the Soviet Sputnik satellite had spurred Americans, fearful of trailing behind their Communist enemy, to boost funding for all areas of science. The National Science Foundation took over from military agencies much of the nation’s support of basic research. One minor consequence was that Keeling got funds to continue the Mauna Loa measurements.
As the Mauna Loa data accumulated, the record grew increasingly impressive, showing

Keeling’s data put a capstone on the structure built by Tyndall, Arrhenius, Plass, and Revelle and Suess. This was not quite the discovery of global warming. It was the discovery of the possibility of global warming. Experts would continue for many years to argue over what would actually happen to the planet’s climate. But no longer could a well-informed scientist dismiss out of hand the possibility that our emission of greenhouse gases would warm the Earth. That odd and unlikely theory now emerged from its cocoon, taking flight as a serious research topic.