When was global warming discovered?

The first serious research conducted on the effect of changes in CO2 levels was in 1896, when Arrhenius completed a laborious numerical computation which suggested that cutting the amount of CO2 in the atmosphere by half could lower the temperature in Europe some 4-5°C (roughly 7-9°F) - that is, to an ice age level. Arrhenius made a calculation for doubling the CO2 in the atmosphere, and estimated it would raise the Earth's temperature some 5-6°C (averaged over all zones of latitude). Arrhenius did not see that as a problem. He figured that if industry continued to burn fuel at the current (1896) rate, it would take perhaps three thousand years for the CO2 level to rise so high. In any case Arrhenius and other researchers were only interested in explaining the Ice Ages. No one seriously believed that global warming was coming. After much criticism, the work of Arrhenius was ignored by the scientific community.

In 1931, an American physicist, E.O. Hulburt, produced calculations supported Arrhenius's estimate that doubling or halving CO2 would bring something like a 4°C rise or fall of surface temperature, but he was a relatively uknown scientist and published his work in a little known Journal.

In 1938 an English engineer, Guy Stewart Callendar, compiled measurements of temperatures from the nineteenth century onwards and confirmed that there was a warming trend. He went on to evaluate old measurements of atmospheric carbon dioxide concentrations and concluded that over the previous hundred years the concentration of the gas had increased by about 10 per cent. Callendar asserted that this could explain the observed warming.

Nevertheless, it was not until the 1970s that scientists began to take the possibility of global warming seriously.