Science of Climate Change

In the two-part article on the Science and Economics of Climate Change, we introduced the basic science of climate change, the different world views of climate economists and climate scientists, and the need for them to talk to each other. In this article, we will take a closer look at the work of scientists who established that greenhouse gases were indeed contributing to global warming and how the measurement of carbon dioxide globally was pioneered in early research in the 1960s and 1970s.

First steps to measure CO₂

In 1953, a young researcher at Caltech, Charles David Keeling, needed to measure CO₂ levels in air and water. He developed a precision manometric system for measuring CO₂, which included an infrared gas analyser and gas flasks for air sampling. (A manometer is an instrument that measures pressure using a column of liquid whose height changes with pressure; essentially, the idea is to compare the pressure to the atmospheric pressure.) In the initial years, he found the CO₂ around Pasadena to be around 310 parts per million (ppm). Later, in collaboration with Revelle of the Scripps Institution of Oceanography and Harry Wexler of the US Weather Bureau, it was decided to undertake CO₂ measurement globally and install observation centers at the South Pole and Mauna Loa in Hawaii. Keeling’s infrared gas analyzer was installed at Mauna Loa in 1958, and the first CO₂ reading recorded was 313 ppm. This has given rise to the famous Keeling Curve, which shows the rise in CO₂ levels since 1958 from 313 ppm to 427 ppm in early 2025.

Keeling’s work was taken forward to explore the link between rising levels of the gas and warming, as well as how much of the rise was attributable to human activity. For this, scientists used bubbles in the ice going back 8,00,000 years to measure the carbon dioxide trapped in these bubbles. This data clearly shows rising levels of carbon dioxide and also confirms the Keeling Curve. The data also show that the industrial period has seen an unprecedented rise in CO₂ levels not seen in the past, and that whenever these levels have risen, warming has occurred. Further, the rise in CO₂ levels coincides with the rise in the consumption of fossil fuels.

Fourier’s Contribution

Fourier was a mathematician and physicist in 1824 and was well known for Fourier analysis, which is the basis of much of theoretical physics even today. Fourier asked a simple question: what keeps the Earth warm? If the Earth radiated most of the heat received from the Sun back into space, it would be rather cold; yet, the Earth is warm and habitable, as if it had an insulating blanket. Fourier gave the example of a glass box with a lid and exposed to sunlight. The air in the box heats up, just as the Earth keeps warm. Later, the Swedish meteorologist Nils Gustaf Ekholm gave this phenomenon a name and called it the Greenhouse Effect (named after greenhouses that are glass boxes which store heat from sunlight and create a favourable temperature for plants). Though Lawrence M. Krauss, in his book The Physics of Climate Change, has called this an unfortunate choice of name because a greenhouse only traps warm air, whereas in Earth’s case, the warm air can rise by convection or transport heat up by conduction.

Fourier found that if the Earth emitted back all the radiation it received from the Sun, the Earth’s temperature would be −18°C. He went through the various steps of physics reasoning and found that the Earth absorbed the infrared radiation emitted upward from its surface, but the radiation from the Sun came to the Earth unchecked (ultraviolet or visible). Not only that, the radiation absorbed by the Earth is re-emitted back to space as well as back to the Earth’s surface. This is basically the Greenhouse Effect and keeps the Earth warm and habitable.

It was John Tyndall (who succeeded Faraday at the Royal Institution in 1853), working in the 1840s, who took forward the work of Fourier and studied the absorption of thermal radiation by different gases. Tyndall was the first to measure carbon dioxide using the earliest version of a spectroscope. A hundred years later, Keeling used more sophisticated instruments to undertake spectroscopy.

Still later, in the early 20th century, Swedish scientist Arrhenius demonstrated that when salts dissolve in water, they break up into separate charged particles and that for most chemical reactions to proceed, heat energy is needed.

Conclusion

The science of climate change is well established today and owes it to pioneers such as Fourier, Tyndall, Arrhenius, and Keeling. Measurement of carbon dioxide and other gases, the link between rising greenhouse gases and warming, the ice-albedo effect, and the feedback loops: these are based on solid science, and our public policies should accordingly take these into cognizance while planning for energy transitions, flood control, electric mobility, battery storage, and renewable energy.