absorbed most of the CO2 that came from people burning fuel. Accordingly, human activity that released carbon would have very little, if any effect at all, on climate because the ocean, as a giant sink, would capture most of it. That was the dominant view over the next several decades.4
“A LARGE-SCALE GEOPHYSICAL EXPERIMENT”
Over the years, Revelle had given some intermittent thought to the Callendar Effect—the argument made by Guy Callendar that increasing CO2 concentrations would raise the earth’s temperatures. His response, based upon his own research going back to his Ph.D., was that Callendar was probably wrong, that Callendar didn’t understand that the ocean would absorb CO2 from the atmosphere. But by the mid-1950s Revelle was beginning to change his mind. The reason emerged from his research on nuclear weapons tests in the Pacific.
After World War II, the Navy enlisted Revelle to help understand the oceanographic effects of those tests. Revelle’s assignment was to devise techniques to measure the waves and water pressure from the explosions. This would enable him to track radioactive diffusion through ocean currents. In the course of this work, Revelle’s team discovered “sharp, sudden” variations in water temperatures at different depths. This was the startling insight—the ocean worked differently from what they had thought. In Revelle’s words, the ocean was “a deck of cards.” Revelle concluded that “the ocean is stratified with a lid of warm water on the cold, and the mixing between them is limited.” That constrained the ability of the ocean to accept CO2.5 It was this period, in the mid-1950s, that Revelle, collaborating with a colleague, Hans Suess, wrote an article that captured this insight and would turn out to be a landmark in climate thinking.
The title made clear what the article was all about: “Carbon Dioxide Exchange Between Atmosphere and Ocean and the Question of an Increase in Atmospheric CO2 During the Past Decades.” Their paper invoked both Arrhenius and Callendar. Yet the article itself reflected ambiguity. Part of it suggested that the oceans would absorb most of the carbon, just as Revelle’s Ph.D. had argued, meaning that there would be no global warming triggered by carbon. Yet another paragraph suggested the opposite; that, while the ocean would absorb CO2, much of that was only on a temporary basis, owing to the chemistry of sea water, and the lack of interchange between warmer and cooler levels, and that the CO2 would seep back into the atmosphere. In other words, on a net basis, the ocean absorbed much less CO2 than expected. If not in the ocean, there was only one place for the carbon to go, and that was back into the atmosphere. That meant that atmospheric concentration of CO2 was destined, inevitably, to rise. The latter assertion was a late addition by Revelle, literally typed on a different kind of paper and then taped onto the original manuscript.
Before sending off the article, Revelle appended a further last-minute thought: The buildup of CO2 “may become significant during future decades if industrial fuel combustion continues to rise exponentially,” he wrote. “Human beings are now carrying out a large scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future.” This last sentence would reverberate down through the years in ways that Revelle could not have imagined. Indeed, it would go on to achieve prophetic status—“quoted more than any other statement in the history of global warming.”6
Yet it was less a warning and more like a reflection. For Revelle was not worried. Like Svante Arrhenius who had tried 60 years earlier to quantify the effect of CO2 on the atmosphere, Revelle did not foresee that increased concentrations would be dangerous. Rather, it was a very interesting scientific question. “Roger wasn’t alarmed at all,” recalled one of his colleagues. “He liked great geophysical experiments. He thought that this would be a grand experiment . . . to study the effect on the ocean of the increase of carbon dioxide in the atmosphere and the mixing between the ocean reservoirs.” (Even a decade later, in 1966, Revelle was arguing that “our attitude” toward rising carbon dioxide in the atmosphere “brought about by our own actions should probably contain more curiosity than apprehension.”)7
At the time, Revelle was deeply involved in planning for an unprecedented global study of how the earth worked that might answer some of the climate questions. This was the IGY—the International Geophysical Year.8
THE UNEXPECTED IMPACT OF THE INTERNATIONAL GEOPHYSICAL YEAR
The International Geophysical Year (IGY)