Guy Stewart Callendar was a British steam engineer who was the first to empirically connect rising CO2 concentrations in the atmosphere with the increase in the Earth’s temperature. Callendar was the first scientist to study climate change in a rigorous and systematic way. In 1938 Callendar published a paper titled The Artificial Production of Carbon Dioxide and Its Influence on Temperature, the first of many articles on the subject. He noted a significant upward trend in temperatures for the first four decades of the 20th century and a continuously rising concentration of atmospheric CO2 since pre-industrial times. He linked this to the combustion of fossil fuels, describing it as an enhanced "greenhouse effect" where infrared radiation is both absorbed and emitted by the extra CO2, causing warming at the Earth's surface. For decades scientists ignored, criticized, or downplayed Callendar’s work, yet research in the 1990s proved his early work to be amazingly accurate considering the level of data monitoring available in the early 1900's.

Sources

• Cleveland, Cutler (Lead Author); Tom Lawrence (Topic Editor). 2008. "Callendar, Guy Stewart." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth December 7, 2006; Last revised August 23, 2008; Retrieved May 16, 2009]. 

Wikipedia Contributors, Guy Stewart Callendar, Wikipedia The Free Encyclopedia, Accessed 16 May 2009.