The meetings of the Physical Society consisted of lectures on the latest scientific developments, many given by Arrhenius himself, followed by discussions that often lasted well into the night. Topics ranged widely, from aeronautics to volcanology. The company spent several sessions considering the tools that would be needed by Salomon August Andrée, another early member of the group, who had decided to try to reach the North Pole in a hot air balloon. (Whatever the quality of his tools, Andrée’s journey would entail his death and the deaths of his two companions.)
One issue of particular interest to the Physics Society was the origin of the ice ages. All over Sweden were the marks of the glaciers which had, for long periods of time, buried the country: rocks with parallel scrapes; strange, sinuous mounds of gravel; huge boulders that had been carried away from their source. But what had brought down the great sheets of ice, carrying everything in front of them? And then what had prompted them to withdraw, allowing the rivers to flow once more and the forests to return? In 1893, the society discussed various theories that had been proposed, including one that linked ice ages to slight variations in the Earth’s orbit. The following year, Arrhenius had a different and, he thought, better idea: carbon dioxide.
Carbon dioxide, he knew, had curious heat-trapping properties. In the atmosphere, it allowed visible light to pass through, but absorbed the long-wave radiation that the Earth was constantly emitting into space. And if, Arrhenius hypothesized, the amount of CO2 was it varied in the air? 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. He lacked crucial information about what wavelengths, exactly, CO2 absorbs. The climate system, meanwhile, is immensely complicated, with feedback loops nested within feedback loops.
Arrhenius, who would later win a Nobel Prize for an unrelated discovery, went ahead anyway. On Christmas Eve 1894 he began building a climate model, the first in the world. He collected temperature data from around the world and made ingenious use of a series of measurements that had been made a decade earlier by an American astronomer, Samuel Pierpont Langley. (Langley had invented a device, a bolometer, for measuring infrared radiation and had used it to determine the moon’s temperature.) Arrhenius performed thousands of calculations, perhaps tens of thousands, and often worked fourteen hours a day on this task. . . He was still calculating as his marriage fell apart. In September 1895, Rudbeck moved out. In November, without having seen Arrhenius again, she gave birth to their son. The following month, Arrhenius finished his work. “I certainly would not have undertaken these tedious calculations if there were no extraordinary interest attached to them,” he wrote.
Arrhenius believed he had solved the mystery of the ice ages, an enigma which “had hitherto proved very difficult to interpret”. He was at least partially right: ice ages are the product of a complex interplay of forces, including wobbles in the Earth’s orbit And changes in atmospheric CO2.
His model turned out to have another use as well. Throughout Europe and North America, coal was shoveled into furnaces that emitted carbon dioxide. By thickening the atmospheric blanket that has warmed the Earth, humans must, reasoned Arrhenius, alter the climate. He calculated that if the amount of carbon dioxide in the air were to double, global temperatures would rise by between three and four degrees Celsius. A few quadrillion calculations later, much more advanced climate models predict a doubling of CO2 it will push temperatures between 2.5 and four degrees Celsius, meaning Arrhenius’ pen-and-paper estimate was, to an ominous degree, on target.
Arrhenius thought the future he had conjured would be delightful. “Our descendants,” he predicted, would live happier lives “under warmer skies.” The prospect was, in any case, distant; doubling atmospheric CO2 it would take, according to him, humanity three thousand years.
It’s easy now to make fun of Arrhenius for his radiance. The doubling threshold could be reached within decades and the results risk being disastrous. But which of us is different? We’re all here, watching things fall apart. Yet deep down, we don’t believe it.