1. 1824 Jean Baptist Joseph Fourier calculates that the Earth is about 33°C warmer than it should be given its distance from the sun and hypothesised that this was due to properties of the Earth’s atmosphere

2. 1859 John Tyndall tests the warming properties of carbon dioxide and finds a reduction in the heat energy (infrared radiation) passing through a test tube containing small amounts of CO 2 – thus demonstrating the heat- trapping properties of this gas

3. 1896 Svante Arrhenius calculates that a 40% decrease or increase in atmospheric CO 2 might cool or warm the world sufficiently to trigger glacial advances or retreats

4. 1938 Guy Callendar calculates that a doubling of atmospheric CO 2 would result in a roughly 2°C rise in average global temperature

5. 1957 Roger Revelle demonstrated that the particular chemistry of sea water prevents it from absorbing all of the excess CO2 emitted through human activities – and that most of the additional CO2 will return to the atmosphere and contribute to warming

6. 1950s and 1960s Charles Keeling begins measuring CO 2 in the atmosphere at Mauna Loa in Hawaii, finding that there are seasonal changes due to uptake and release of CO 2 in the Northern Hemisphere’s forests, but that the atmospheric concentration was rising steadily