A belief that carbon dioxide and its radiative properties may be important in regulatingclimate and its variability is not new. In 1859, the Irish-born John Tyndall began studying theradiative properties of various gases ^[31]. Tyndall constructed the firstratio spectrometer to measure the absorptive power of gases, including water vapour and carbondioxide, and identified significant differences in the abilities of various gases to absorb andtransmit radiant energy. He showed that molecules of water vapour, carbon dioxide and ozone are thebest absorbers of heat radiation, and that even in small quantities these gases absorb much morestrongly than the atmosphere itself. Tyndall concluded that, among the constituents of theatmosphere, water vapour is the strongest absorber of radiant heat and is therefore the mostimportant gas controlling the surface temperature of the earth. Without water vapour, he concluded,the earth s surface would be held fast in the iron grip of frost . He later speculated on howfluctuations in water vapour and carbon dioxide could be related to climate change.