Guy Stewart Callendar

• 1. Introduction

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  Guy Stewart Callendar was an English steam engineer who, in 1938, did something no professional climate scientist had managed. He showed that the land surface of the Earth had grown warmer across the previous fifty years. He did it as a hobby, with no computer, while his day job involved turbines and boilers. Callendar did not see danger in what he found. He believed the warming would be welcome, because it might hold off a "return of the deadly glaciers." So how did an engineer with a damaged eye and a certificate in mechanics end up ahead of the experts? Why did the men who ran Britain's weather institutions dismiss him? And how did a lone amateur's idea eventually shape the measurements that the world now relies on?

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• 2. A Laboratory Childhood

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  Guy Callendar was born in Montreal on the 9th of February 1898, in a city where his father, Hugh Longbourne Callendar, held the chair of physics at McGill College. Hugh was an expert in thermodynamics, the science of heat and its movement. His career carried the family back to the United Kingdom, first to University College London as Quain Professor of Physics. After four years there he moved again, taking a personal chair at Imperial College London. The children grew up among visiting members of the scientific elite, so serious science was ordinary dinner-table company. At the age of five, Guy suffered an injury that shaped his whole life. His elder brother Leslie stuck a pin in his left eye, and the damage left Guy partially blinded. That injury would soon decide where he spent the First World War.

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• 3. Steam and the War Years

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  In 1913 Callendar enrolled at St Paul's School, but he left in 1915 as the First World War reshaped every plan. His impaired sight made him unfit for military service. Instead he joined his father's laboratory at Imperial College, working as an assistant to the Air Ministry's X-ray Committee. His tasks included testing varied apparatus, among it aircraft engines at the Royal Aircraft Factory in Farnborough. When peace returned, he began a course in Mechanics and Mathematics at City and Guilds College, part of Imperial, in 1919. Three years later he graduated with a certificate in those subjects. That qualification opened full-time work beside his father, studying how steam behaves under high temperatures and pressures. A research association representing turbine manufacturers, the British Electrical and Allied Industries Research Association, backed this work. Later his research turned toward batteries and fuel cells, though a very different question was already occupying his spare hours.

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• 4. Climate as a Sideline

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  Callendar never held a post as a climatologist; he treated the subject as a pastime. He built on the ideas of nineteenth-century scientists, among them Svante Arrhenius and Nils Gustaf Ekholm. Arrhenius had earlier proposed that carbon dioxide in the air could influence temperature, and the link is now called the Callendar effect. Callendar's own method was patient comparison. He gathered temperature measurements stretching from the 1800s onward and set them beside old readings of atmospheric carbon dioxide. The two records rose together, and he argued that the gas could explain the warming. He also put a number on the Earth's sensitivity to the gas, assessing climate sensitivity at 2 °C. That figure sits at the low end of the range later given by the IPCC. Modern researchers have judged his estimates remarkably accurate, especially given that he worked without a computer. Between 1938 and 1964 he published 10 major scientific articles and 25 shorter ones, covering global warming, infra-red radiation and carbon dioxide produced by human activity.

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• 5. A Slow Vindication

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  Sir George Simpson, then director of the British Meteorological Society, read Callendar's results and concluded they must be a coincidence. His doubt reflected a wider mood. Scientists had argued over the carbon dioxide idea in the early twentieth century, and the following decades leaned sceptical. Even so, Callendar's work changed the conversation. His papers through the 1940s and 1950s slowly persuaded some colleagues that carbon dioxide in the atmosphere needed an organised research programme. That push led, eventually, to Charles Keeling's measurements at the Mauna Loa Observatory, which began in 1958 and proved pivotal for the theory of human-caused global warming. Gilbert Plass and Keeling both expanded on Callendar's work in the 1950s and 1960s. Callendar himself never saw mainstream opinion fully turn. He died on the 3rd of October 1964, still certain his theory was right.

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