Charles D. Keeling was an American pioneer in the monitoring of carbon dioxide concentrations in the atmosphere. Widely recognized as the "Keeling curve," the atmospheric carbon dioxide concentration measurements, taken since 1958 at the Mauna Loa Observatory in Hawaii, constitute the longest, continuous record of atmospheric carbon dioxide concentrations available in the world. These measurements are considered to be a reliable indicator of the regional trend in the concentration of atmospheric carbon dioxide in the middle layers of the troposphere. The Mauna Loa record shows a continuous increase in the annual concentration of carbon dioxide, an important greenhouse gas, and thus is one indication of human contribution to global climate change. Each year, the atmospheric carbon dioxide concentration varies between a high value in winter (because of biospheric respiration) and a low value in summer (because of drawdown by photosynthesis); as a result, a wave-like pattern is superimposed on the year-to-year increasing trend. Dr. Keeling's research has shown that the atmospheric concentration of carbon dioxide has grown from 315 parts per million (ppm) in 1958 to 380 (ppm) in 2005 with increases correlated to fossil fuel emissions.

Sources

• Alejandra Roman (Lead Author); Cutler J. Cleveland (Contributing Author); Alan Sweedler and Sidney Draggan (Topic Editors). 2008. "Keeling, Charles D.." 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 September 20, 2006; Last revised August 21, 2008; Retrieved May 17, 2009]. 
• Wikipedia Contributors, Charles David Keeling, Wikipedia The Free Encyclopedia, Accessed 18 May 2009.