Cobra Effect · Weather and climate
A year of sums about carbon dioxide
How a chemist with a pencil made the first estimate of global warming.
7 cards, read aloud in 2:48, with a test and sources.
In the 1890s, Svante Arrhenius wanted to know what caused the ice ages.
Arrhenius was a Swedish chemist in Stockholm. Scientists knew that great sheets of ice had once covered much of northern Europe. But nobody knew why the climate could swing so far. Arrhenius suspected the carbon dioxide in the air.
He set out to calculate how much carbon dioxide warms the Earth.
He used measurements of heat rays from the Moon, made by the American astronomer Samuel Langley. From them he worked out how much heat the air absorbs, band by band of latitude and season by season. All of it was done by hand. He later said the calculations took him about a year.
In 1896, he published his answer.
Cutting the carbon dioxide in the air to around half, he calculated, could cool the Earth enough for an ice age. Doubling it would warm the Earth by around five or six degrees. It was the first estimate of its kind.
A colleague pointed out that people were adding carbon dioxide to the air.
Arvid Högbom had been studying where carbon dioxide comes from, including the burning of coal. Factories and furnaces were releasing it on a growing scale. But Arrhenius thought a doubling would take thousands of years.
Arrhenius thought a warmer world would be a good thing.
In a book published in 1908, he wrote that people might enjoy more equable and better climates, especially in the colder parts of the Earth. He hoped warmth might help grow food for a rising population. By then he had won a Nobel Prize, in 1903, for quite different work in chemistry.
He was badly wrong about how fast it would happen, and not far off about how much.
Carbon dioxide has risen far faster than he expected, as the burning of coal, oil and gas grew enormously. By 2025, it was about half as high again as before industry began. Today’s best estimate for a doubling is about three degrees of warming. His figure was on the high side, but close for pencil and paper.
So when a calculation says something surprising, ask what it assumes.
Arrhenius’s physics was broadly sound. What he got wrong was how quickly people would burn fuel. How much warming a gas causes, and how fast the gas builds up, depend on different things. A good forecast needs both.
Sources
- The first paper on carbon dioxide and global warming, British Library Science blog. Arrhenius’s 1896 paper and what it calculated.
- Future Calculations, Science History Institute. How Arrhenius came to his estimate, and what he thought it meant.
- On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground, Svante Arrhenius, 1896, via the Royal Society of Chemistry. The original paper.
Nearby ideas
- The gases that trap heat. How two experiments showed that a few invisible gases keep the Earth warm.
- The curve that tracks carbon dioxide. How patient measurements on a Hawaiian volcano revealed carbon dioxide rising.
- The first public weather forecasts. How a storm, a telegraph and a sea captain gave us the weather forecast.
- The rounded number that changed the forecast. How a rounded number revealed why the weather can't be forecast far ahead.
- The warm water that shifts the world’s weather. How warm water off Peru turned out to steer rain and drought around the world.
- The climate model that passed the test of time. How a simple computer model predicted climate change decades before it arrived.