Initial Conditions Episode 2: Arrhenius, Callendar, and Keeling

Initial Conditions Episode 2: Arrhenius, Callendar, and Keeling

The images, texts, and details that did not make it into this week’s episode of Initial Conditions: A Physics History Podcast

Growing up in the 1990s and 2000s, I thought (for those who “follow the science,” at least) climate change was a long-settled issue. It turns out that, as with many topics in the history of science, it took a while for scientists to agree on the causes of climate change. Even then, it took longer for them to agree about the threat climate change poses. Talk to any climatologist long enough, and you’ll hear that there remain many questions yet to be answered about climate change.

Svante Arrhenius, Guy Callendar, and Charles David “C.D.” Keeling represented three successive generations of climate scientists. Many others helped build the foundations of what we know about climate change, of course, but in this episode we had to simplify our story for the sake of time (check out Spencer Weart’s book The Discovery of Global Warming and website to find out more). Still, the three individuals we focus on this week did a lot to put climate change—anthropogenic climate change, more specifically—on solid ground. Amidst their professional work we can see their personalities emerge, proving that they were fascinating people in their own rights. In the second episode of Initial Conditions: A Physics History Podcast, we inform listeners about how Arrhenius, Callendar, and Keeling were men of their times, for better or worse.

A portrait of Svante Arrhenius, circa 1907.

Portrait of Svante Arrhenius.

Media Credits

AIP Emilio Segrè Visual Archives, Arrhenius Svante A1.

Svante Arrhenius (1859-1927) was born in Sweden, near Uppsala University, where his father held an administrative post. He had a close relationship with his father, who encouraged young Svante to pursue his interest in mathematics. As he grew older, Arrhenius would sometimes take solace in math, especially after a tumultuous divorce from his first wife and former student, Sofia Rudbeck. As the divorce was finalized, Rudbeck took custody of Arrhenius’s firstborn son, moving with him to an island off the Swedish coast. His son’s new home was not terribly far by contemporary standards, but quite far for Arrhenius. During Arrhenius’s lifetime, Sweden industrialized, bringing speedy train service to more and more cities, towns, and villages in the predominantly rural nation.

These two connected factors—industrialization and the ensuing technological changes he witnessed in his native Sweden—contextualize the scientific issues that drew Arrhenius’s attention. In 1896, Arrhenius published a paper titled “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground,” in which he used his outsized mathematical talent to demonstrate how increasing concentrations of carbon dioxide could increase the earth’s average surface temperature. In Worlds in the Making, published for a general audience in 1908, Arrhenius presented the idea that the carbon dioxide that humans generated through the burning of fossil fuels could increase the average global temperature. So began a debate about the causes and effects of anthropogenic climate change that would last for most of the rest of the twentieth century. Arrhenius’s work on anthropogenic climate change (which, I should mention, constituted just a minority of his scientific research–he spent more time studying physical chemistry) was likely influenced by the changes he saw taking place in his native Sweden, which was quickly becoming an industrialized nation.

Arrhenius’s conclusions about the effects of climate change were quite different than the ones we have today. He wrote that a warming Earth could help Sweden by providing longer growing seasons and an abundance of crops. In fact, he was concerned about preserving Swedish coal reserves for future generations, so that they too could experience the benefits of fossil fuels and a warming climate. Again, the place and time where and when Arrhenius studied anthropogenic climate change matter greatly. Sweden is located in Northern Europe. It has a short growing season and long, cold winters. Arrhenius’s ideas about climate change might sound odd to modern readers, but they made sense in a predominantly agricultural society. Nearly a century after his death, Arrhenius’s conclusions have put him at odds with Greta Thunberg, a leading advocate for immediate and drastic steps to combat climate change and his distant relative. 

Arrhenius put anthropogenic climate change on the scientific agenda. Yet, as his thoughts about climate change reveal, the actual effects of a changing climate were still poorly understood in the early twentieth century. Successive generations would continue investigating climate change, revealing that the future might not be quite as rosy as Arrhenius hoped.

Guy S. Callendar sitting outdoors.

Guy S. Callendar sitting outdoors.

Credit: University of East Anglia Archive, contact the University of East Anglia Archive about this image. NBLA may be able to provide copyright contact information. Please contact us. Catalog ID Callendar Guy B2.

Guy Callendar (1898-1964) had no formal scientific training. The highest degree he earned was a certificate in steam engineering from Imperial College, in the United Kingdom, where his father held an academic position. Like Arrhenius, Callendar was studious and driven, spending hours recording tedious details about two subjects in particular: steam engines and weather patterns. Also like Arrhenius, Callendar was encouraged by his father to pursue his research interests. In turn, Callendar would propel the study of anthropogenic climate change forward.

Callendar was born in Montreal but grew up in southern England, where his father, Hugh, accepted a professorship soon after Guy’s birth. Hugh was a trained physicist, and like many of his peers, greatly enjoyed tinkering with mechanical objects. In this episode you’ll hear about some of his follies in that area; he was lucky not to have seriously harmed his wife or children. The same can’t be said of Guy’s older brother Leslie, who blinded young Guy in one eye after sticking a needle in it and later blew up his family’s laboratory while trying to make TNT. Despite his injuries and whatever other trauma Leslie inflicted on him, Guy Callendar went on to have a successful career as a steam engineer. Guy had another passion, however: weather observations. Callendar wrote meticulous journal entries about daily weather conditions, perhaps spurred by his love of tennis, which requires calm weather.

At some point in his life, Guy turned his attention to atmospheric carbon dioxide concentrations. He pursued his study of accurate annual atmospheric carbon dioxide measurements with as much determination as he did steam tables and the weather. Callendar eventually established a measure of the average concentration of atmospheric carbon dioxide in the nineteenth century at 290 parts per million. After doing so, he was able to show how the concentration of carbon dioxide had increased during the twentieth century, and determine what that might mean for the average global surface temperature. His work culminated in an important paper that he presented at the 1937 meeting of the Royal Meteorological Society. Guy’s work was received with some praise and much criticism. The scientific community was not ready to accept Callendar’s conclusions, which ran against the common assumption at the time that the oceans, among other carbon sinks, could absorb excess carbon dioxide from fossil fuels. Guy, furthermore, believed that global warming might not be the worst thing for the planet; perhaps, he thought, it could help prevent another ice age, which scientists at the time understood were periodic events. Of course, our understanding of the potential hazards of increasing concentrations of carbon dioxide in the atmosphere has improved since Callendar’s time.

Guy refined his research over the next two decades. By the 1950s he came to believe that climate change might pose a more serious threat than he had initially thought. In the meantime, climatology had started to emerge as a field in its own right, and some scientists were beginning to agree that anthropogenic climate change was, if anything, a subject worth studying. Guy did a great deal to move the field of climate change research in new directions. His accomplishments are all the more remarkable when we remember that he did so without holding any advanced scientific degrees.

A portrait of Charles David Keeling.

Portrait of Charles Keeling of Scripps Institution of Oceanography, University of California, San Diego and winner of American Geophysical Union (AGU) Maurice Ewing Award, 1991.

Media Credits

American Geophysical Union (AGU), courtesy AIP Emilio Segrè Visual Archives.

As with Arrhenius and Callendar, Ralph Keeling, C.D.'s father, supported his son's interest in science. In turn, C.D. Keeling did much to encourage his son Ralph (likely named for his grandfather) to study climate change; Ralph would later take his father’s position at the Scripps Institution of Oceanography. In that way, Keeling fits into the pattern of fathers and sons and climate change research.

C.D. Keeling (1928-2005), like Callendar, was quite observant. He loved the outdoors and built instruments that would allow him to capture and analyze the fresh air of the Pacific Northwest.  After taking a position at Scripps, Keeling had access to monitoring stations around the world, and—like Callendar—began to try to figure out how the concentration of carbon dioxide in the Earth’s atmosphere was changing. Keeling conducted his research at a time when climate science was beginning to emerge as a fully-fledged field. It would take time and money—money was a perennial problem if you listen to meteorologist Lester Machta here—to bring the field to where it is today. Keeling helped put climate change research on a solid footing by showing in a simple and concise way that a real and fundamental change was happening in the earth’s atmosphere.

Keeling is best known for the Keeling curve, a simple yet powerful graphic representation of carbon dioxide concentrations in the atmosphere over time. It reveals that the concentration of carbon dioxide in the atmosphere has been increasing (at an increasing rate) since the mid-1950s, when Keeling began his research. It vindicates Callendar and Arrhenius by showing that they were right, and many proto-climatologists were wrong; the oceans could not absorb all of the additional carbon dioxide being put into the atmosphere by fossil fuels. Keeling resolved that debate, but the question of what all that CO2 meant for the climate and life on Earth was yet to be fully understood. Before passing away in 2005, Keeling was able to glimpse how climatologists were beginning to answer that question.

The Keeling Curve, which shows the atmospheric concentration of carbon dioxide from 1958 to the present day.

The Keeling Curve, which shows the atmospheric concentration of carbon dioxide from 1958 to the present day.

Media Credits

Scripps Institution of Oceanography

Arrhenius, Callendar, and Keeling represented three successive generations of climate science. Each put a finer point on the question of what all of those fossil fuels were doing to the atmosphere. They revealed—slowly, over time, and moving from the realm of mathematics to natural phenomena that could be observed and measured—that much of the carbon dioxide released from burning fossil fuels was staying in the atmosphere. Their work also shows how science changes and adjusts as new information becomes available. Individuals who have been born since the late twentieth century have grown up knowing about the reality of climate change (if the community they were raised in “followed the science”--an important caveat). This was not the case for most of the twentieth century, and in fact it has been a fairly recent development. The history of physics is full of such changes, as well as the coincidences and patterns we discuss in this episode. 

To learn more about climate history, visit

You can listen to Initial Conditions: A Physics History Podcast wherever you get your podcasts. A new episode will be released every Thursday so be sure to subscribe! On our website, you will find transcripts, show notes, and our suggested resources to learn more about each topic we discuss. 


Crawford, Elizabeth. Arrhenius: From Ionic Theory to the Greenhouse Effect. Canton, MA: Science History Publications, 1996.

Fleming, James Rodger. The Callendar Effect: The Life and Work of Guy Stewart Callendar (1898-1964), The Scientist Who Established the Carbon Dioxide Theory of Climate Change. Boston: American Meteorological Society, 2009.

Fleming, James Rodger. Historical Perspectives on Climate Change. New York and Oxford: Oxford University Press, 1998.

Weart, Spencer. The Discovery of Global Warming: Revised and Expanded Edition. Cambridge: Harvard University Press, 2008.


About the Author

Justin Shapiro

Justin Shapiro outside portrait

Justin Shapiro. Image credit: Hyun Joo Kim

Justin Shapiro is a historian of the environment and technology. His interests include environmental justice, climate history, the environmental history of cities, and the history of infrastructure. His most recent publication can be found in the October 2022 issue of the Journal of Transport History. During his time at NBL&A, Justin has enjoyed researching the history of climate science, the history of the African American presence in physics, and pseudoscience, among other topics.

See all articles by Justin Shapiro.

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