Scientists have understood the basic physics of climate change for roughly 200 years. The idea that certain gases in the atmosphere trap heat dates to the 1820s, and the first experimental proof that carbon dioxide warms the air was published in 1856. Far from being a recent discovery, the science of human-caused warming built steadily across two centuries, with each generation adding sharper detail to a picture that was already taking shape long before the first coal-fired power plant.
The 1820s: Heat Trapped by the Atmosphere
The story begins with French mathematician Joseph Fourier, who in the 1820s proposed that Earth’s atmosphere retains heat from the sun, keeping the planet warmer than it would otherwise be. Fourier didn’t have the tools to identify which gases were responsible, but he recognized that the atmosphere acts as an insulating layer. His cryptic references to the way a greenhouse traps warmth gave later writers the term “greenhouse effect,” even though Fourier himself never used that phrase in the modern sense.
1856: The First CO₂ Experiment
American scientist Eunice Newton Foote conducted the earliest known experiment linking carbon dioxide to atmospheric warming. In 1856, she placed glass cylinders filled with different gases in direct sunlight and measured how hot they got. Her conclusion was blunt: “The highest effect of the sun’s rays I have found to be in carbonic acid gas,” the old name for carbon dioxide. She went further, writing that an atmosphere rich in CO₂ “would give to our earth a high temperature,” and that higher concentrations of the gas in the geologic past could explain why the planet was once warmer. This is the earliest experimentally verified statement that CO₂ concentrations drive global warming.
Three years later, Irish physicist John Tyndall built a more sophisticated apparatus, the first ratio spectrophotometer, to measure how different gases absorb heat radiation. He confirmed that oxygen, nitrogen, and hydrogen are essentially transparent to heat, while water vapor, carbon dioxide, and ozone absorb it strongly. Tyndall identified water vapor as the most powerful heat-trapping gas and speculated that fluctuations in water vapor and CO₂ could drive changes in climate. By 1859, the core mechanism of the greenhouse effect had been demonstrated in a laboratory.
1896: The First Warming Calculation
Swedish chemist Svante Arrhenius took the next logical step. In 1896, he sat down with pencil and paper and worked out what would happen to global temperatures if the amount of CO₂ in the atmosphere doubled. His answer: Earth’s surface would warm by 11°F to 14.5°F. That estimate was too high by modern standards, but the direction was right, and the calculation showed for the first time that burning fossil fuels could, over time, meaningfully change the climate. Arrhenius saw this as a slow process playing out over thousands of years. He didn’t foresee how quickly industrialization would accelerate.
1938: Connecting Fossil Fuels to Measured Warming
By the late 1930s, enough temperature records existed for someone to check whether the warming Arrhenius predicted was actually happening. British engineer Guy Stewart Callendar compiled global temperature data and matched it against fossil fuel combustion figures. He calculated that humanity had added about 150 billion tons of CO₂ to the atmosphere in the preceding half-century, roughly three-quarters of which had stayed in the air. From this, he estimated temperatures were rising at about 0.003°C per year. The number sounds tiny, but Callendar’s key insight was that the warming was real, measurable, and tied directly to the burning of coal and oil. The phenomenon became known as the Callendar Effect.
1958: Tracking CO₂ in Real Time
Everything before this point relied on snapshots and estimates. That changed in 1958, when geochemist Charles David Keeling set up instruments at the Mauna Loa Observatory in Hawaii to measure atmospheric CO₂ continuously. On the first day of operation, the equipment recorded a concentration of 313 parts per million. Keeling kept measuring, and within a few years the data revealed a relentless upward trend overlaid with seasonal breathing (CO₂ dips each spring as Northern Hemisphere plants absorb it, then rises again in fall). The resulting graph, now called the Keeling Curve, became one of the most iconic datasets in all of science. Today the reading at Mauna Loa exceeds 420 ppm.
1965: The White House Gets a Warning
The U.S. government was formally told about the risks of climate change in 1965, when President Lyndon B. Johnson’s Science Advisory Committee published a report titled “Restoring the Quality of Our Environment.” The report stated plainly that fossil fuel combustion was the only major new source of atmospheric CO₂ and that it had increased the total amount of CO₂ in the atmosphere and ocean by roughly 7% between 1860 and 1960. The authors predicted melting ice caps, rising sea levels, and acidification of water sources. They warned that by the year 2000, atmospheric CO₂ would increase by close to 25%, enough to produce “measurable and perhaps marked changes in climate.” They also posed a question still relevant today: what happens if all recoverable fossil fuel reserves are burned? At then-current rates of consumption growth, they estimated that threshold could be reached within 150 years.
1979: Pinning Down the Numbers
By the late 1970s, computer models had matured enough to give more precise estimates. In 1979, the National Academy of Sciences convened a panel led by meteorologist Jule Charney to assess the state of the science. The resulting Charney Report concluded that doubling atmospheric CO₂ would warm Earth’s surface by 1.5°C to 4.5°C, with the most probable value near 3°C. Greater warming was expected at high latitudes, near the poles.
That range, 1.5°C to 4.5°C for a doubling of CO₂, proved remarkably durable. It held up through four decades of subsequent research and was only narrowed slightly (to 2.5°C to 4°C) by the Intergovernmental Panel on Climate Change in its 2021 assessment. The fact that scientists in 1979 landed on essentially the same answer as scientists with supercomputers in 2021 speaks to how well the underlying physics was already understood.
1988: Climate Change Enters Public Debate
The moment climate change shifted from a scientific concern to a public and political one is often traced to the summer of 1988. NASA climate scientist James Hansen testified before the U.S. Senate during a punishing heat wave, telling lawmakers that the warming of Earth’s surface over the past century was well established and that there was “a high degree of confidence that humans have been a significant contributor to this warming.” Hansen’s testimony made front-page news and catalyzed the creation of the IPCC that same year, establishing the framework for international climate assessments that continues today.
What the Timeline Reveals
The physics of the greenhouse effect is older than the light bulb. The first experimental proof that CO₂ warms the air predates the Civil War. The first quantitative prediction of fossil-fuel-driven warming came before the invention of the automobile. A formal warning reached the president’s desk in 1965, when atmospheric CO₂ was still below 320 ppm. By 1979, the scientific community had converged on a temperature sensitivity range that has barely shifted since. The science of climate change is not new, uncertain, or sudden. It is one of the longest-running research programs in modern science, built layer by layer across two centuries by physicists, chemists, meteorologists, and geologists working on different continents and in different eras, all arriving at the same fundamental conclusion.