Our understanding of how certain atmospheric gases trap heat dates back almost 200 years to 1824 when Joseph Fourier described what we know as the greenhouse effect. Fourier, a French mathematician and physicist, asked what seems to be a simple question: why doesn’t the planet keep heating up as it receives sunlight? What is regulating our atmospheric temperature?

Knowing that heated surfaces emit radiation (thermal energy), Fourier reasoned that the Earth would emit radiation absorbed by the Sun back into space – resulting in an icy planet. There must be something regulating the temperature – emitting enough thermal energy to keep the planet from freezing and overheating. Not too hot, not too cold.

Fourier’s answer to these questions is formalized in what we now call the greenhouse gas effect. From the American Institute of Physics history of climate change page:

How does the Earth’s blanket of air impede the outgoing heat radiation? Fourier tried to explain his insight by comparing the Earth with its covering of air to a box with a glass cover. That was a well-known experiment — the box's interior warms up when sunlight enters while the heat cannot escape. This was an over simple explanation, for it is quite different physics that keeps heat inside an actual glass box, or similarly in a greenhouse. (As Fourier knew, the main effect of the glass is to keep the air, heated by contact with sun-warmed surfaces, from wafting away. The glass does also keep heat radiation from escaping, but that's less important.) Nevertheless, people took up his analogy and trapping of heat by the atmosphere eventually came to be called "the greenhouse effect.

Fourier’s work was instrumental in understanding climate change. Years after Fourier’s death on May 16, 1830, scientists continued to ask questions about the greenhouse gas effect. In 1862, John Tyndall discovered that certain gases (water and carbon dioxide) help trap heat from escaping the atmosphere. Later, in 1895, Swedish Chemist Svante Arrhenius observed the infrared-absorbing properties of carbon dioxide and water molecules.

We still see the impact of Fourier’s answer today, with the recent news that atmospheric carbon dioxide measurements surpassed 400 parts per million, and the ongoing debates of how to limit and adapt to a changing climate. It is, you might say, a hot topic.