How the work of one of the greatest scientists of the 20th century laid the foundation for our modern relationship with the planet.
Geopolitics on the move
Sixty-six years ago, this day exactly, America found itself celebrating one of founding fathers of modern meteorology. For the very first time, on Dec 17th 1956, the coveted cover of Time magazine went to a meteorologist.
This was not the first instance that a scientist had earned such public recognition. Since the inception of the magazine in 1923 there had been a steady stream of science celebrities gracing its cover. But most of them had been associated with the advances of the second industrial revolution, a steady stream of technologists and medical doctors who had improved the material conditions of the magazine’s readers.
There were others too, of course. Albert Einstein had been portrayed at least three times. Sigmund Freud twice. A smattering of explorers with the occasional exotic creature had also been featured. But there had never been someone who had made a career out of thinking about the Earth and how it functions. No one who had trained their inquiry towards the quantitative examination of the planet.
That changed sixty-six years ago. It was a turning point: one could say it was when the concern for the planet made it into the shop window of public culture. And the person who was afforded this honor was the Swedish-American meteorologist Carl-Gustaf Rossby.
The choice and timing were not entirely coincidental. The cover article opened with the first launch of the rocket Viking. Great expectations rested on this mission, for it was going to revolutionize humanity’s ability to monitor the Earth in service of operational weather forecasting. 1956 was a trial, which was supposed to lead, two years later, to taking America’s first satellite to space. But at that point satellites were far more than scientific enterprises. They were the symptoms of a new international order.
Over half a century earlier, another Swede — Rudolf Kjellen — had introduced the idea that the physical nature of geography was a powerful determinant of the relationships between states. He called it “geopolitics.” By the time of the magazine cover featuring Rossby most political scientists had turned against the notion of geopolitics, one that had inspired Hitler in his expansionist dreams. But the fact is that the planet had become the theatre of war, and the relationship between geography and international politics had, if anything, tightened.
Soon after Churchill had announced that an iron curtain had descended across Europe, the Cold War had begun. Its scope was going to be nothing less than the planet itself. The technologies that had been honed during the two previous world wars — the vast modern air carrying fleets that projected power over the seas, the growing arsenal of submarine vehicles that would become the dominant deterrent of the second half of the twentieth century, the long-range planes that could carry the nuclear bomb anywhere on the planet — had expanded the range of power projection, turning the oceans and the atmosphere into the principal theatre of this new war, with the outer reaches of the atmosphere itself as the sole real boundary.
That outer boundary, the imaginary sphere that was the limit of humanity’s range, was a contested space, in which satellites were tactical infrastructure. Indeed, less than a year after the cover of Time, in October 1957, Russia successfully placed its first satellite, Sputnik, on a rapid orbit around the planet. As the tiny spherical satellite made its beeping journey across the sky, Americans panicked. It was the Viking program that was supposed to herald American supremacy in space, not a product of Nikita Kruschev’s planned economy. The arms race had begun.
In this context, Rossby’s square face on Time magazine was a crucial symbol of western scientific supremacy over the global commons. People had begun to look at the planet as a whole and ask questions about how it behaved, because that was now the theatre of a new, simmering conflict. And those who studied that theatre — those armed with the instruments of twentieth century physics and capable of predicting its behavior — were going to take center stage.
Rossby represented a generation of Earth scientists who would be propelled by military funding and geopolitical concerns to the very heart of the Cold War conflict.
An artist’s rendition
The artist Boris Artzybasheff, a Ukrainian-born American illustrator known for his magazine covers and for his curious representations of anthropomorphic war machines, had drawn Rossby’s portrait for the cover of Time. Artzybasheff attempted a synthesis of his subject’s life work, of what it meant to be a “weatherman” in 1956.
The picture has a layered, metaphysical quality to it. In the far background, a split sky: fair weather and a few innocuous white clouds on the right; on the left a storm gathers, as a single stroke of lightning discharges towards the ground through an oblique sheet of rain.
The divided sky was an apt representation for Rossby’s intellectual roots. The Swede’s career had started in Bergen, under the tutelage of Vilhelm Bjerknes, a giant of 20th century science with impeccable scientific lineage. Through his father Carl-Anton, Vilhelm descended from the great nineteenth century mathematical schools of Cauchy and Dirichlet and the physical tradition of James Clerk Maxwell, and had been responsible for bringing meteorology into the seam of modern physical science.
Vilhelm and his son, Jacob Bjerknes, had proposed a theory to explain the behavior of the weather systems that came in from the Atlantic, bringing with them storms over Sweden. They introduced the idea of weather fronts, discontinuities in pressure and temperature fields at the surface resulting from air masses, cold and warm, descending as if on a battlefield, and confronting each other as they swept across the landscape.
In this theory fronts formed along the “Polar front,” a strong north to south temperature gradient in the subpolar region. Initially small perturbations would bend the front, forming cold and warm fronts that would circle around a low pressure like cooked spaghetti circling an open sink drain. From that point on, wartime metaphors were inevitably abundant. The warm, lighter front would lead warm air from the south to slide over the cold air, forming high stratiform clouds.
The cold front, meanwhile, would lead heavy, polar air from the north to “attack” behind the warm front, moving under it and pushing warm, moist air up into cumulus clouds that would release rain or snow. This theory went on to establish the so-called Bergen School, which made of frontogenesis, the life-cycle of a mid-latitude weather system, the center piece of meteorology. And that is what Rossby was trained in.
One of the important characteristics of the Bergen approach was that it increased the predictability of weather. Its supported were keen to make sure that it would spread, so, in 1926, Rossby made it over to the United States on a fellowship. He settled in at the National Weather Bureau, where he intended to proselytize its meteorologists into this new discipline.
As would happen, the sixty-year-old meteorological institution proved impermeable to change, and Rossby struggled to convince his peers. He did not however face the same challenge with the practitioners of the newly established commercial flight sector.
In May of 1927, Charles Lindbergh had flown alone the Spirit of St. Louis from New York to Paris. After the flight, he went on a tour of all states. In the fall of that same year he headed for Mexico and South America. In December of 1927, dissatisfied with the poor forecast of the National Weather Bureau and evidently aware of the potential of the Bergen school’s approach, Lindbergh asked Rossby to provide him with a weather forecast for his trip from Washington DC to Mexico City. The forecast was indeed useful, marking the beginning of an important convergence of interests between the aviation industry and the spread of meteorology.
The incident created a minor scandal, and Rossby left the bureau, but his future in the United States was set.
The industrialization of Earth Sciences
In the center of Artzybasheff’s portrait, a square-faced Carl-Gustaf, pipe in hand, looks on, surrounded by a weather map that spills into the foreground. The picture suggests the great meteorologist is deep in thought, possibly puzzled by the very weather map that surrounds him, a look of bemused disappointment washing over his face.
That may well have been Artzybasheff’s intention, conscious that he had surrounded the most famous meteorologist in America with a somewhat haphazard placement of synoptic elements. It was an artist’s rendition of what a weather map looks like, a fact made clear by the incongruous series of fronts — a sequence of cold, warm, and stationary fronts — drawn to thread through the magazine’s title.
Rossby might have objected to the quality of the map but it did capture the spirit of his work. Early on in his career in Stockholm, he had been a synoptic meteorologist, diligently mapping measurements on maps to support weather forecasting. He was involved in balloon and kite measurements, as well as the odd sea-going campaign, a hands-on meteorologist.
In Artzybasheff’s map, the tiny black and white circles represented weather station measurements of cloud cover and temperature. Their perimeter was tailed by a vector that indicated wind direction and strength. In the picture they are somewhat liberally sprinkled across the pressure field, in some cases looking unsure of which direction to take. There is even a solitary ‘S’, a symbol for a northern hemisphere hurricane, right next to Rossby’s left ear, although the pressure measurements hardly suggest the possibility of hurricane strength winds. Weather measurements, so prominent in the portrait, were central not just to Rossby’s experience but to Earth sciences more broadly.
It is easy to forget just how transformative the first decades of the twentieth century had been, not just for the war, but for the technological leaps they had witnessed. While Rossby was coming of age as a scientist, in the span of twenty years, commercial flights had gone from a dream to a booming industrializing sector. The United States was the natural home for an industry with the potential of gluing the vast continental nation into an unprecedented cohesive unity.
Aviation was also at the heart of the changing nature of international relations. In the early part of the 20thcentury, and despite the disastrous events of the first world war, the British navy was still the uncontested supreme power on the seas of the world. But aspirations of hegemony on America’s part had far less competition in the sky. It is for that reason that, for example, Roosevelt’s foreign policy all through the Second World War was to secure airport access to American airlines, hoping to expand commercial connectivity.
But to operationalize flights on such a large scale, both domestically and internationally, one had to deal with the fact that the sky did not always cooperate. Reliable weather forecasting was essential, not just for the solitary adventurers like Lindbergh, but for the thousands of crafts that would have to make up the industry.
Having left the bureau in 1928, Rossby ended up going to California to do just that, and set up a weather reporting system. Western Air Express was flying between Los Angeles and San Francisco and needed better forecasts than what one might get by calling up the destination at departure and hoping to encounter the same weather by landing time. Rossby organized a system of reporting, taking advantage of gas stations and other stationary businesses he found along the route.
Flight was still a relative novelty. Rossby resorted to the occasional stunt, borrowing a plane and pilot, to mesmerize rural communities into cooperating with a program of regular weather measurement. It worked. The system was successful. It was eventually adopted by other airlines, the beginning of the dense monitoring system that to this day — although automated — supports the National Weather Service.
But Rossby’s days as an operational practitioner were rapidly coming to an end.
The philosopher kings of the modern age
Maybe the most prominent feature of Artzybasheff’s picture are the long, curved isobars — lines of constant atmospheric pressure at the surface — which form a sequence of high- and low-pressure systems just above Rossby’s head. In fact, those ridges and troughs form a wave train that bears his name. His work on this phenomenon was the foundation of modern dynamic meteorology.
Up to the second world war, the economy of the United States was still heavily dependent on the productivity of its agriculture. The US seemed committed to realizing the vision that John Wesley Powell had laid out decades earlier for the American west: a land tamed by modern arid agronomics and superior water management. The first half of the 20th century was also when the Bureau of Reclamation and the Army Corp built some of the iconic structures of the modern American landscape, from Hoover Dam to the All-American Canal.
Homesteading had created a vast federal nation, moving thousands of citizens westward. It had prepared America to become the breadbasket of the world. The First World War had proved an unexpected geopolitical fracture. The British Empire emerged bankrupt and on its knees. Russia, the other great grain producer of the northern hemisphere, was engulfed in revolution. America had become the producer of last resort, paid in hard currency by a world starved from the war and the collapse of nineteenth century globalization.
But this huge economic and geopolitical dependence on the American landscape had also revealed an extremely vulnerable nation. In 1927, a perfect storm had led to the biggest flood in US history, when levees broke on the lower Mississippi. The costs of that disaster commanded a third of the federal budget, and the recovery he guided propelled Hoover to the presidency. In the 1930s, the dust bowl had shown just how susceptible to drought the extensively farmed landscapes of the Great plains were.
In the face of such destructive forces, weather forecasting was an existential matter. Rossby found himself at the heart of an intellectual call to arms to try and master the behavior of the elements. In 1928, after his western exploits with the airline industry, he had been called to establish the Meteorology department at the Massachusetts Institute of Technology.
Up to then, measurements had been confined to the ground, but at MIT Rossby advocated for airborne measurements. As measurements accumulated, Rossby was able to finally take a huge conceptual leap, developing a theory to explain and predict the long waves — now called the Rossby waves — that encircle the planet, travelling west to east. These are the waves around which Bjerknes’ fronts form, and whose behavior television meteorologists the world over describe every evening.
In a 1939 seminal paper Rossby provided an elegant and profound synthesis of Newtonian physics applied to the macroscopic behavior of the planet’s atmosphere. The basic principle was as old as Newtonian physics: conservation of angular momentum, the same principle that a skater uses to increase her spin by drawing her arms close to her body.
Rossby realized that the atmosphere is a fluid moving on a rotating planet. As such, it possesses a background vorticity, a spin that is determined by compounding its movement with the movement of the planet itself. He also know from looking at all the data that the high and low pressures on synoptic maps were simply vortices, themselves endowed with a certain amount of rotation.
Because the atmosphere is squashed by gravity to mostly travel along the surface of the planet, as it moves north or south in latitude it moves closer or further away from the axis of rotation, thus acquiring or loosing background spin as it does. Therefore, any atmospheric vortex — with its own spin relative to the surface of the planet — would have to accelerate or slow accordingly, in order to compensate for the change. This basic insight provided Rossby with the physical basis for explaining a wave motion, one in which the restoring force that produces the oscillation is the background gradient in the spin imparted to the atmosphere by the rotation of the planet.
The paper was deceptively simple. Rossby had opened the door to a formalization of atmospheric science which would lead only a few years later to the first computer models of the atmosphere. The project, sponsored by John von Neumann, would be led by one of Rossby’s most famous students, Jule Charney.
That was not the only insight Rossby brought to the field. His 1939 paper was not published in an obvious atmospheric journal. Rather, it was published in the Journal of Marine Research. By then Rossby had realized that many of the results that were relevant to the atmosphere would have found application in the ocean too. These were the first steps towards a unification which would happen only a few years later with the first coupled models of the climate system.
Rossby’s contributions continued into the Second World War and included some of the first explanations for the jet stream. But his most lasting legacy is a clever application of classical physics to the problems of the atmosphere, the same physics of the Manhattan project, of the rocket scientists, of NASA. That application had opened the door to a new field, a mathematically described planet Earth, one in which the most salient phenomena could be predicted and — it was thought at the time — maybe controlled.
The physics that had delivered the nuclear age was, it turns out, also responsible for a new mode of understanding our home, and Rossby was possibly its greatest interpreter.
Rossby died unexpectedly less than a year after the 1956 issue of Time magazine that had him on the cover. His legacy on meteorology and climatology is so foundational that it is impossible to imagine our understanding of the climate system without him.
The story of science is often told as one of singular heroes. In reality, it is mostly a process of incremental accretion, one in which the scientific endeavor finds its strength. But occasionally some people do embody the confluence of both historical and intellectual events of such importance as to become motors of progress. Carl-Gustaf Rossby was one of those people.
The Time magazine cover article ends with Rossby’s work on carbon emissions, to which he devoted the last years of his life. “There is a good possibility that man’s fires and engines are adding so much of it [CO2] to the atmosphere that the world’s climate may be changed drastically by the solar heat that it traps. Rossby wants to find out about this little matter too” quipped the article. The sixty-sixth anniversary of that cover is a useful reminder of the fact that the risks we face today had not escaped him. He sounded the alarm long, long ago.
Rossby understood that changing the chemistry of the atmosphere could be dangerous. Thanks to his work, dynamic meteorology — one of the great scientific advances of the twentieth century — had established a quantitative link between sunlight, the thermal structure and movement of the atmosphere, and how it weather events could change in ways that were economically salient.
The fact that predicting rain and wind or estimating the likelihood of floods or droughts could be framed as a physical problem, susceptible to the mathematical instruments of modern physics, had transformed meteorology into an operational field. It had also provided the instruments to peer quantitatively into the future. And what Rossby saw already then was that the radiative effect of long-lived greenhouse gases in the atmosphere was of grave concern.
Rossby warned us of the risks. The article closed on Rossby’s prescient words: “Tampering can be dangerous. Nature can be vengeful. We should have a great deal of respect for the planet on which we live.” Indeed.
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