What would a depressed Swedish chemist, alone in the Nordic winter as his marriage to his beautiful research assistant collapsed, do on a Christmas Eve? Go out on the town and find himself a new partner? Give way to maudlin sentiment? Well, in Svante Arrhenius鈥檚 case, no. On 24 December 1894, he rolled up his sleeves and began a marathon of mathematical calculation that took him more than a year, often working 14 hours a day.
By the end he had virtually invented the theory of global warming caused by the greenhouse effect, and with it the principles of modern climate modelling. Not only that, his figure for the intensity of warming for a given increase of carbon dioxide in the atmosphere is almost identical to that calculated by the Intergovernmental Panel on Climate Change. Unfortunately, when Arrhenius completed his sums nobody was remotely interested.
SVANTE ARRHENIUS was an obdurate fellow with a long-standing reputation for rubbing his colleagues up the wrong way. As day-long darkness gave way to months of midnight sun, he laboured on, filling book after book with tedious calculations of the impact of changing concentrations of greenhouse gases on every part of the globe 鈥� calculations that would take today鈥檚 supercomputers only seconds.
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鈥淚t is unbelievable that so trifling a matter has cost me a full year,鈥� he later confided. But with his wife Sofia gone he had few distractions. And the calculations had become an obsession.
What initially spurred the work was the urge to answer a popular riddle of the day: how the world might have cooled during the ice ages. His calculations showed that a reduction in atmospheric CO2 levels of between a third and a half would cool the planet by 4 to 5 掳C 鈥� enough to cover most of northern Europe in permanent ice. Eighty years later, researchers found just such levels of CO2 in air trapped in Antarctic ice during the last ice age.
But as he reached the end of his calculations, Arrhenius was also becoming intrigued by the potential of rising concentrations of greenhouse gases to trigger global warming. He concluded that a doubling of atmospheric CO2 would raise world temperatures by an average 5 to 6 掳C.
How did he do it? His methods were remarkably close to those used by modern modellers. He started with some basic formulae on the ability of gases such as CO2 and water vapour to trap heat in the atmosphere, derived by 19th-century luminaries such as French mathematician Jean Baptiste Fourier.
The gases, as Fourier knew, let through ultraviolet radiation from the Sun. But the Earth鈥檚 surface converted much of this radiation into infrared heat, which greenhouse gases could trap in the atmosphere, causing it to warm. Fourier never explored this. It was Arrhenius who first realised that the effect was a kind of atmospheric thermostat.
The temperature at which the thermostat was set, he saw, depended on how much ultraviolet radiation the surface of the Earth reflected back into space, and how much it converted into infrared heat. And that depended on whether the surface was coated in ice or ocean, forest or grassland or was shrouded in cloud.
Armed with Fourier鈥檚 equations, Arrhenius set about dividing the surface of the planet into small squares and assessing the capacity of each segment to absorb and reflect solar radiation. From this he produced a series of temperature predictions for different latitudes and seasons determined by atmospheric concentrations of CO2 that varied from two-thirds to three times the then current value.
Most remarkably, his calculation that a doubling of CO2 levels would cause a warming of around 5 to 6 掳C almost exactly mirrors the Intergovernmental Panel on Climate Change鈥檚 most recent assessment, which puts 5.8 掳C at the top of its likely warming range.
Arrhenius published his findings in a paper, 鈥淥n the influence of carbonic acid in the air upon the temperature of the ground鈥�, presented to the Stockholm Physical Society in 1895. As well as getting the global numbers spectacularly right, he picked out many of the same key elements as modern predictions. High latitudes would experience greater warming than the tropics, he said. Warming would be more marked at night, in winter and over the land.
But he had cracked a problem that seemed to interest no one else. So everyone forgot all about it 鈥� until the 1990s, when his century-old work on global warming became one of the most referenced scientific sources of the decade.
Luckily, this labour was but a sideshow in Arrhenius鈥檚 career. Not long after completing his work on climate, he found fame as the winner of the 1903 Nobel Prize for Chemistry, for work on the electrical conductivity of salt solutions. Soon, too, he had a new wife and child.
Arrhenius was a polymath, dabbling in everything from immunology to electrical engineering. He was an early investigator of the Northern Lights and a proponent of the idea that the seeds of life could travel through space.
But after the First World War, his mood changed. The optimism of his generation, who had believed that science and technology could solve every problem, crumbled in the face of anxieties about the future. He took up political causes and was an outspoken critic of attempts by both religions and business to stifle the publication of inconvenient scientific results. He campaigned for immunisation against smallpox, and had a passionate interest in agricultural self-sufficiency, fired by the hunger suffered by Swedes during the war.
He railed against the wastefulness of modern industrial society and began to fear that the world would run out of key resources. 鈥淐oncern about our raw materials casts a dark shadow over mankind,鈥� he wrote. 鈥淥ur descendants surely will censure us for having squandered their just birthright.鈥�
Arrhenius鈥檚 great fear was that oil supplies would dry up, and he predicted that the US might pump its last barrel in 1935. He advocated energy efficiency and proposed the development of renewable energy, such as wind and solar power, and engines that ran on alcohol. He sat on a government commission that made Sweden one of the first countries to develop hydroelectric power.
Many Swedes see Arrhenius as a pioneer of modern environmentalism for his efforts to counter the threat of global warming with new forms of energy. But it was not so simple. For one thing, he never made the connection between his work on the greenhouse effect and his later nightmares about disappearing fossil fuels.
He knew well enough that burning coal and oil generated greenhouse gases that would build up in the air. But in his earlier writings he had concluded that it would probably take a millennium to cause a significant warming. And when he later began to perceive the scale of industrial exploitation of fossil fuels, he failed to add up the facts: his fear was solely that the resources would run out.
The main reason for his blindness was probably that he thought a spot of warming might be rather a good thing. In 1908 he wrote: 鈥淲e may hope to enjoy ages with more equable and better climates, especially as regards the colder regions of the Earth, ages when the Earth will bring forth much more abundant crops for the benefit of a rapidly propagating mankind.鈥�
It is possible that as he wrote this he was harking back to the time he embarked on his mathematical marathon. To someone sitting alone in the bitter cold with an inadequate coal fire, a little heat may well have seemed enticing.
