In 1896, Swedish scientist Svante Arrhenius took off into the atmosphere. Or at least into an immense calculation about the atmosphere that might distract him from having divorced his wife Sofia, who had taken custody of their baby son Olof. He looked to the skies to settle a key argument: How can landscapes around the world show evidence of ice scraping over it?
At the time, the idea of an ice age was controversial, and the world’s great minds struggled to explain the mile-thick sheets clues suggested had existed. For months Svante laboured by hand to calculate how tiny reductions in a gas called carbon dioxide – CO2 – could team up with water vapour to cool down the world. He didn’t produce an immediate answer to the riddle of the ice age, and he may or may not have escaped the woes of his personal life. But Svante Arrhenius did lay a foundation that climate science still rests upon today.
The tools that Svante used had recently been forged in the furnace of scientific progress that was the 19th century. Until then, even an effect as seemingly basic as heat had been poorly understood. Only slowly had the idea that it was a kind of fluid or gas been replaced by the modern understanding that it’s a flow of energy. In the 1820s French mathematician Joseph Fourier helped drive that shift. He also mused on why, when the Sun heats the Earth, doesn’t the Earth get as hot as the Sun?
The opaque greenhouse
Joseph’s answer was another relatively recent discovery – infrared radiation. But when he calculated what Earth’s temperature would be after emitting heat energy into space as invisible infrared, he got an answer well below freezing. Knowing something must be wrong, Joseph realised that Earth’s atmosphere keeps some infrared radiation in. He likened it to a pane of glass over a box that keeps the air beneath warm. Svante and other scientists repeatedly returned to this idea, partly explaining why today we call the extra warming from the atmosphere the ‘greenhouse effect’.
Most scientists thought that infrared radiation and the gases mingling in the atmosphere didn’t affect each other, but British physicist John Tyndall went hunting for absorbers regardless. Yet even after hundreds of experiments he found it passed straight through the atmosphere’s main gases, oxygen and nitrogen. On the point of giving up, the story goes, he turned to coal gas. Then used for lighting and piped straight into his lab, this was a mixture including mainly methane, also the main component of natural gas. When it came to stopping infrared, he found coal gas was ‘as opaque as a plank of wood’.
That success drove John on to try other gases, finding water vapour and CO2 were infrared absorbers, among many others. As the atmosphere holds between twice and 100 times as much moisture as CO2, its overall greenhouse warming effect is therefore much larger. But Svante realised that CO2’s seemingly tiny role was a crucial one, because of one important fact: warmer air holds more moisture. Any slight temperature shifts that changes in CO2 levels brought would change air’s moisture content, creating an extra effect on temperature. So perhaps CO2 produced by volcanoes could create significant warming on the planet, and a period without eruptions could spiral down into an ice age. That insight remains important today, with the amplification that water creates called feedback, and CO2′s driving influence called forcing.
By including humidity in some epic computations, Svante showed that CO2 could have a surprisingly large impact on the Earth’s surface. Much like climate modellers today divide the world into zones for their calculations, he divided it into strips of latitude. For each one he made two main calculations: heat energy entering and leaving as radiation, and moisture levels in the air. And while the knowledge he was armed with meant he couldn’t include many aspects of the real world, he did reveal CO2’s potential power.
Halving CO2 levels would reduce temperatures by 5°C, equivalent to the ice age in parts of the world, Svante wrote. Meanwhile, trebling CO2 levels could increase temperature by up to 9°C. To check that such a CO2 change could be possible he asked a colleague, Arvind Högbom, who said there was “no conceivable hindrance to imagining” different levels. He also noted that beyond natural sources like volcanoes, humans were also adding CO2. The coal burned each year equated to about one-thousandth of the level in the air in that period, Arvind worked out.
Though Svante was a leading scientist of his age, becoming the first Swede to be awarded the Nobel Prize in chemistry in 1905, his CO2 work was soon considered completely wrong. Experiments seemed to prove the world already had the greatest greenhouse effect it could, though these were later also shown to be flawed. And with people generally believing that any technological change was for the better, they were unaware that burning coal might be a problem.
Today Svante’s idea has been proved right, with CO2’s climate forcing role well-established, and a matter for great concern. It’s also part of the answer to the riddle of how ice ages happen, though it took decades more for the full picture to emerge. Through the rest of the year I’ll be charting this journey, and others that sprung from it. I’ll be writing monthly blog entries tracking how we got from the 18th century’s first steps to modern climate science, through individual scientists’ stories. I think it will be interesting, and I’ve got good company in that. Svante himself liked to write about science by considering researchers who came before. “The study of the views and reasonings of past ages sheds a remarkable light on our own,” he wrote in his book, The Life of The Universe. “It allows us to trace… our modern theories from the shadowy notions of antiquity.” And there’s a lot to look back on, with almost 200 years of lessons from climate research to prepare us for the future.
Spencer Weart’s book, ‘The Discovery of Global Warming’ is the source of much of the historical material in this post.
Burgess, E. (1837). “General Remarks on the Temperature of the Terrestrial Globe and the Planetary Spaces; by Baron Fourier.” Translation from the French, of Fourier, J. B. J., 1824, “Remarques Générales Sur Les Températures Du Globe Terrestre Et Des Espaces Planétaires. American Journal of Science, 32, 1-20
Tyndall, P. (1860). The Bakerian Lecture: On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation, Absorption, and Conduction. Proceedings of the Royal Society of London, 11, 100-104 DOI: 10.1098/rspl.1860.0021
Arrhenius, S. (1896). On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground Philosophical Magazine Series 5, 41 (251), 237-276 DOI: 10.1080/14786449608620846