The Callendar effect: Here's how this man connected humans to global warming in 1938

Feb 25, 2022

Guy Callendar theorized that humans were unknowingly raising Earth’s temperature by burning fossil fuels in furnaces and factories. Image: UNSPLASH/Chris LeBoutillier

Sylvia G. Dee

Assistant Professor of Earth, Environmental and Planetary Sciences, Rice University

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Extract page from a book about global warming.

A page from Guy Callendar’s 1938 paper shows how he tracked and calculated CO2 changes, all in his spare time. Image: GS Callendar

A tweet with graphs showing changes in global temperature.

Callendar found global average temperatures that match with current estimates of the average temperatures of the time. Image: Ed Hawkins/Twitter

A black and white photo of a man, Guy Callendar.

Guy Stewart Callendar in 1934. Image: G.S. Callendar Archive/University of East Anglia

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