Lifting the fog of war and climate

FIDO (Fog Investigation Dispersal Operations) petrol burners are ignited on either side of the main runway at Graveley, Huntingdonshire, as an Avro Lancaster of No. 35 Squadron RAF takes off in deteriorating weather, 28 May 1945. Guy Callendar helped devise the FIDO system.

• This is part two of a two-part post. Read part one here.

In November 1943, the British Royal Air Force used a new secret weapon in anger for the first time. Called FIDO, or Fog Investigation and Dispersal Operation, it was a system of petrol burners that cleared fogbound airfields by raising their temperatures several degrees. It let the Allies launch and land warplanes safely when their enemies were still grounded by poor visibility. Newspapers billed it as near miraculous, crediting it with shortening the war and saving the lives of 10,000 airmen. But for one of the engineers behind it, Guy Callendar, it was just another way to combine his interest in weather and climate with his heat expertise.

From 1922-1941 Guy had worked on the Callendar Steam Tables, which he filled with data to help other engineers and scientists working with steam equipment. But after a decade carefully measuring the interaction between temperature, pressure and other properties in steam, his thoughts turned increasingly to climate. By 1938 he had stood up in front of a room of sceptical meteorologists, telling them that the world was warming, and burning fossil fuels was the cause. And while that marked a key turning point in identifying and understanding global warming, his later work in collecting evidence for that argument may have been still more important.

With his CO2 theory getting a frosty reception, and with his steam work winding down, Guy scoured scientific papers for evidence to back his argument. Since scientists like Svante Arrhenius had first suggested an important role for CO2 in climate in the 19^th century and even earlier, physics had made some important advances. Earlier scientists knew that gases like CO2 absorbed infrared radiation but in the 1920s they made leaps forward in understanding why.

The frequency of the wave of infrared radiation, the number of oscillations it goes through per second, matches motions in the gas molecules that absorb it. For example, if the molecules spin at a similar frequency to the radiation’s oscillations, they can absorb the its energy. Also, atoms such as oxygen and carbon in the molecule can move, pushed by thermal energy and pulled by chemical bonds between them. That creates a vibration, and if the frequency of the vibration matches that of the infrared radiation, the vibration can absorb the radiation’s energy

Good vibrations

Understanding this, scientists were soon using infrared frequencies that different chemicals absorb to find out more about how atoms were connected up in them. But to be definite about the chemical structures, the frequency measurements had to be spot-on. By 1936, physicists at the University of Michigan made final measurements confirming that CO2 was basically a straight line – a carbon atom between two oxygens.

Initially, Guy was less concerned by CO2’s structure than the precise data, and getting it into a format that could be used to study its role in the atmosphere. He gathered measurements on CO2 from reports written in several languages together in one place where others could get them easily, much like he had for steam. From that he estimated that at atmospheric temperatures, CO2, water and other gases absorbed as much as 2/3 of the energy the warm Earth emitted as infrared radiation. Preventing that energy reaching space makes the planet warm enough for us to live on, but adding more CO2 by burning traps yet more heat.

Atmospheric windows: Wavelengths where electromagnetic radiation penetrates the Earth’s atmosphere (grey) and where gases absorb it (black). Chemical notation (CO2, O3) indicates the gas responsible for blocking a particular wavelength. Credit: NASA

When Guy took these insights to the Royal Meteorological Society in 1941, as he had before, he found a much less hostile audience. One member even stood up to congratulate Guy on showing that CO2 absorption was “rather more important than had been thought in the past”. And knowing that his career was about to change direction, Guy even hinted that he might be able to help out when another scientist stressed the need for more data. “The problem of improving on existing data is rather formidable and would require strong financial support on a five or ten year basis,” he said. “But it would be well worthwhile in providing a greater understanding of fundamental processes.”

That call appears to have been well received. In 1942, the Royal Society asked him to do a similar job for many other chemicals found floating in the atmosphere. But with the Second World War in progress, Guy was assigned to defence research soon after, where he helped use infrared radiation to understand the chemical structure of German fuel. Then, for his work on FIDO he moved to the Armament Research Department at Langhurst in south-east England, where he worked until his retirement in 1958.

The final analysis

Guy Callendar clearing snow at his house after a blizzard in December 1962, part of a short-term cooling trend that shook his confidence in his theories. Credit: The Callendar Effect, American Meterological Society, see citation below.

Though defence research was his full-time job, Guy continued his work on climate in his spare time. And soon after the Second World War ended, other scientists started reporting rising temperatures, retreating glaciers in Iceland and decreasing Arctic ice thickness. Against that backdrop, Guy started trying to get his message out to a wider audience. In 1949, he wrote a defining explanation of what burning more fossil fuel does in Weather magazine.

“Reduced to its simplest terms this theory depends on the fact that, whereas CO2 is almost completely transparent to solar radiation, it is partially opaque to the heat which is radiated back into space from the earth. In this way it acts as a heat trap, allowing the temperature near the earth’s surface to rise above the level it would attain if there were no CO2 in the air. It may be said that the climates of the world are behaving in a manner which suggests that slightly more solar heat is being retained in the atmosphere. This could be due to its increasing opacity to terrestrial heat as a result of the additions of CO2.”

Guy’s ideas spread, and he was happy when Charles Keeling set up a permanent base to measure CO2 in 1958, ultimately confirming his own effort to bring together other observations that showed rising levels. And after his retirement, he returned to his classic 1938 paper in 1961, more than doubling the number of weather stations he used to construct a worldwide temperature average. Despite the masses of manual calculations this must have taken, he was modest with his findings, merely concluding that they didn’t rule out his CO2 theory. In fact, a recent reanalysis has showed that they agree closely with modern records showing clear warming.

That modesty may have reflected an element of self-doubt, as the Earth embarked on a period of cooling in the 1950s and 1960s that shook his confidence. That trend continued as he finally finished recording his beloved personal weather journal in October 1964. The month shows just one entry in an almost empty grid, as Guy died on October 3. But even if he did doubt the value of his work in his last days, Guy Callendar had almost single-handedly made clear that CO2 could drive climate change. His work has influenced scientists ever since – notably Charles Keeling, who later wrote to Guy’s daughter Anne, looking to access his papers on CO2 levels before 1900. “There is currently much interest on the possible impact of increasing atmospheric CO2 on climate,” he wrote. “Considerable attention is focussed on the detail of your late father’s pioneering work.”

Further reading:

Spencer Weart’s book, ‘The Discovery of Global Warming’ has been the starting point for this series of blog posts on the key players in the history of climate change.

This post’s length can be blamed on James Fleming’s fascinating biography of Guy Callendar, called “The Callendar Effect”.

Callendar, G. (1938). The artificial production of carbon dioxide and its influence on temperature Quarterly Journal of the Royal Meteorological Society, 64 (275), 223-240 DOI: 10.1002/qj.49706427503
Callendar, G. (1941). Infra-red absorption by carbon dioxide, with special reference to atmospheric radiation Quarterly Journal of the Royal Meteorological Society, 67 (291), 263-275 DOI: 10.1002/qj.49706729105
Sutherland, G., & Callendar, G. (1942). The infra-red spectra of atmospheric gases other than water vapour Reports on Progress in Physics, 9 (1), 18-28 DOI: 10.1088/0034-4885/9/1/304
Callendar, G. (1949). CAN CARBON DIOXIDE INFLUENCE CLIMATE? Weather, 4 (10), 310-314 DOI: 10.1002/j.1477-8696.1949.tb00952.x
Callendar, G. (1961). Temperature fluctuations and trends over the earth Quarterly Journal of the Royal Meteorological Society, 87 (371), 1-12 DOI: 10.1002/qj.49708737102