In the 1820s, Joseph Fourier proposed the greenhouse effect to explain why Earth’s temperature was higher than the sun’s energy alone could explain. Earth’s atmosphere is transparent to sunlight, so sunlight reaches the surface where it is converted to heat. However, the atmosphere is not transparent to heat radiating from the surface, and captures some of that heat which warms the planet.[337] In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide. She concluded that “An atmosphere of that gas would give to our earth a high temperature…”[338][339] Starting in 1859,[340] John Tyndall established that nitrogen and oxygen—together totalling 99% of dry air—are transparent to radiated heat. However, water vapour and some gases (in particular methane and carbon dioxide) absorb radiated heat and re-radiate that heat within the atmosphere. Tyndall proposed that changes in the concentrations of these gases may have caused climatic changes in the past, including ice ages.[341]

Svante Arrhenius noted that water vapour in air continuously varied, but the CO2 concentration in air was influenced by long-term geological processes. At the end of an ice age, warming from increased CO2 levels would increase the amount of water vapour, amplifying warming in a feedback loop. In 1896, he published the first climate model of its kind, showing that halving of CO2 levels could have produced the drop in temperature initiating the ice age. Arrhenius calculated the temperature increase expected from doubling CO2 to be around 5–6 °C.[342] Other scientists were initially sceptical and believed the greenhouse effect to be saturated so that adding more CO2 would make no difference. They thought climate would be self-regulating.[343] From 1938 onwards Guy Stewart Callendar published evidence that climate was warming and CO2 levels rising,[344] but his calculations met the same objections.[343]

In the 1950s, Gilbert Plass created a detailed computer model that included different atmospheric layers and the infrared spectrum. This model predicted that increasing CO2 levels would cause warming. Around the same time, Hans Suess found evidence that CO2 levels had been rising, and Roger Revelle showed that the oceans would not absorb the increase. The two scientists subsequently helped Charles Keeling to begin a record of continued increase, which has been termed the “Keeling Curve”.[343] Scientists alerted the public,[345] and the dangers were highlighted at James Hansen’s 1988 Congressional testimony.[21] The Intergovernmental Panel on Climate Change, set up in 1988 to provide formal advice to the world’s governments, spurred interdisciplinary research.[346] https://en.m.wikipedia.org/wiki/Climate_change