There us a widespread impression that the fact of global warming was only discovered recently. This is wrong.
The idea has been around for more than a century but it was only really put on the scientific map through the tremendous research of the British meteorologist and steam engineer Guy Callendar. He published a ground-breaking paper in 1938. A year later he reported a 7% increase in anthropogenic CO2 since 1900, the result of industrial emissions, the burning of fossil fuel:
“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. From the best laboratory observations it appears that the principal result of increasing CO2… would be a gradual increase in the mean temperature of the colder regions of the earth” (too little data was available for the southern hemisphere at that time).
Quarterly Journal Royal Meteorological Society (1939).