The Artificial Production of Carbon Dioxide and its Influence on Temperature
Burning coal is already warming the planet — measured, and put to a number, in 1938.
In 1938 a steam engineer, working in his spare time, claimed that burning coal was already warming the whole planet — and he put a number on it.
The idea, unpacked
Sunlight warms the ground; the warm ground glows back with invisible infrared heat, which escapes to space. Carbon dioxide in the air catches some of that outgoing heat and sends part of it back down — so the more CO₂ there is, the warmer the surface must run to keep its books balanced.
Guy Callendar's key insight was answering an old objection. Water vapour also traps heat, and there is far more of it, so most scientists had decided extra CO₂ couldn't matter. But new measurements showed CO₂ absorbs heat at exactly the wavelengths water vapour lets through. Adding CO₂ closes that window — and Callendar calculated that doubling it would warm the Earth by about 2 °C.
Where it came from
Callendar was a British combustion engineer, not a meteorologist. In his own time he gathered temperature records from some 200 weather stations around the world, collected old measurements of atmospheric carbon dioxide, and showed that both had risen together over the previous half-century — the warming tracking the gas. He presented it to the Royal Meteorological Society in 1938.
The reception was cool. Senior figures like Sir George Simpson doubted that an amateur could overturn the settled view that water vapour ruled the climate and CO₂ was a footnote. The carbon-dioxide theory had been dismissed for decades; Callendar, almost alone, brought it back — which is why the human warming effect still carries his name.
Why it mattered
This was the first real evidence that humans, by burning fossil fuels, were measurably changing the climate of the whole planet. Callendar revived a theory everyone had abandoned, gave it numbers that were close to right, and set the agenda for everything that followed: measure the rising CO₂, pin down how sensitive the temperature is, and build the models. The phenomenon is named the Callendar effect after him.
An analogy
Think of the atmosphere as a pane of glass over the Earth. Sunlight passes straight through and warms the ground; the ground gives off invisible heat that the glass partly blocks, keeping the inside warm — the greenhouse effect. Water vapour is one pane, already there. Callendar's point was that CO₂ is a second pane that darkens a part of the window the first one leaves clear. Add more of that second pane and the room warms — even a little extra is enough. Slide the CO₂ up in the tool below and watch the thermometer climb.
Where it sits
Callendar stands in a clear line. Joseph Fourier first described the greenhouse effect (1824); John Tyndall measured which gases trap heat (1859); Svante Arrhenius made the first calculation of CO₂ warming (1896, in this Library). Callendar revived their idea with real observations in 1938. After him, Gilbert Plass sharpened the physics (1956), Charles Keeling proved CO₂ was rising with his famous curve (1958, in this Library), and Manabe and Wetherald built the first trustworthy climate model (1967, in this Library). He is the bridge between Arrhenius's prediction and Keeling's proof.
By fuel combustion man has added about 150,000 million tons of carbon dioxide to the air during the past half century.
In conclusion it may be said that the combustion of fossil fuel .. is likely to prove beneficial to mankind in several ways, besides the provision of heat and power.