Today Guy Callendar is a historical footnote, but tomorrow he will have a chapter of his own. Born in 1898, Callendar was the son of Britain’s leading steam engineer, a successful academic and inventor who raised his children in a 22-room mansion. A greenhouse on the grounds was converted into a laboratory for the children until one of Callendar’s three brothers blew it up trying to make TNT. The same brother put out Callendar’s left eye. Undeterred by the subsequent lack of depth perception, he became his father’s successor as the nation’s most important steam engineer. None of this is why Guy Callendar’s name will be boldfaced in tomorrow’s textbooks. Instead it will be because he was willing to delve into fields he knew nothing about, atmospheric science among them. Nobody knows why he got so interested in the air. Callendar himself attributed it to ordinary curiosity: “As man is now changing the composition of the atmosphere at a rate which must be very exceptional on the geological time-scale, it is natural to seek for the probable effects of such a change.” In the early 1930s Callendar began collecting measurements of the properties of gases, the structure of the atmosphere,…