Svante Arrhenius was, by nature, an optimist. He believed that science should – and could – be accessible to everyone. In 1891 he got his first teaching job at an experimental university in Stockholm called Högskola. That same year, he founded the Stockholm Physics Society, which meets every other Saturday evening. For a fee of one Swedish krona anyone could join. Among the earliest members of the society was a Högskola student named Sofia Rudbeck, who was described by a contemporary as both “an excellent chemist” and “a ravishing beauty”. Arrhenius began to write his poetry, and soon the two were married.
Physics Society meetings consisted of lectures on the latest scientific developments, many of which were delivered by Arrhenius himself, followed by discussions that often lasted late into the night. The subjects were very varied, from aeronautics to volcanology. The company devoted several sessions to examining the instruments needed by Salomon August Andrée, another early member of the group, who had decided to try to reach the North Pole by balloon. (Regardless of the quality of his instruments, Andrée’s trip will result in his death and that of his two companions.)
A question which particularly interested the Physical Society was the origin of the ice ages. Everywhere in Sweden, signs of the glaciers which had, for long periods, buried the country: parallel scraping rocks; strange winding heaps of gravel; huge boulders that had been transported far from their source. But what had caused the great ice caps to descend, taking everything before them? And then what had driven them back, allowing the rivers to flow again and the forests to return? In 1893, the society debated various theories that had been proposed, including one linking ice ages to slight variations in Earth’s orbit. The following year, Arrhenius came up with a different and, according to him, better idea: carbon dioxide.
Carbon dioxide, he knew, had curious heat-trapping properties. In the atmosphere, it lets visible light through, but it absorbs the longer wave radiation that the Earth is constantly emitting into space. What if, Arrhenius speculated, the amount of CO2 in the air had varied? Could this explain the ebb and flow of glaciers?
The mathematics involved in testing this theory went far beyond what was possible at the time. Arrhenius didn’t have a calculator, let alone a computer. It lacked crucial information about the wavelengths of, exactly, CO2 absorbed. The climate system, on the other hand, is extremely complicated, with feedback loops nested within feedback loops.
Arrhenius, who would later win a Nobel Prize for an unrelated discovery, dived anyway. On Christmas Eve 1894, he began building a climate model, the first in the world. He gathered temperature data from around the world and made ingenious use of a set of measurements taken a decade earlier by an American astronomer, Samuel Pierpont Langley. (Langley had invented a device – a bolometer – to measure infrared radiation and used it to determine the temperature of the moon.) Arrhenius performed thousands of calculations – perhaps tens of thousands – and often worked on this task for fourteen hours a day. . He was still calculating as his marriage fell apart. In September 1895, Rudbeck moved. In November, without having seen Arrhenius again, she gave birth to their son. The following month, Arrhenius completed his work. “I certainly would not have undertaken these tedious calculations if an extraordinary interest had not been attached to them”, he writes.
Arrhenius believed he had solved the mystery of the ice ages, a riddle which had “so far proved the most difficult to interpret”. He was at least partly right: ice ages are the product of a complex interplay of forces, including oscillations in Earth’s orbit. and variations in atmospheric CO2.
His model also turned out to have another use. Throughout Europe and North America, coal was shoveled into kilns that emitted carbon dioxide. By thickening the atmospheric blanket that has warmed the Earth, humans must, Arrhenius reasoned, alter the climate. He calculated that if the amount of carbon dioxide in the air were to double, global temperatures would rise between three and four degrees Celsius. A few quadrillions of calculations later, much more advanced climate models predict that the doubling of CO2 will cause temperatures to soar between 2.5 and 4 degrees Celsius, meaning Arrhenius’ estimate with pen and paper was, to an odd degree, on target.
Arrhenius thought the future he had conjured up would be delightful. “Our descendants,” he predicted, would live happier lives “under warmer skies.” The prospect was, in any case, distant; double atmospheric CO2 would take, according to him, three thousand years to humanity.
It’s easy now to mock Arrhenius for his sunshine. The doubling threshold could be reached in a few decades, and the results could be disastrous. But who among us is different? We’re all here watching things fall apart. And yet, deep down inside, we don’t believe it.