Charles David Keeling was an American scientist whose recording of carbon dioxide at the Mauna Loa Observatory first alerted the world to the possibility of anthropogenic contribution to the "greenhouse effect" and global warming. The Keeling Curve measures the progressive buildup of carbon dioxide, a greenhouse gas, in the atmosphere. He was born on April 20, 1928 in Scranton, Pennsylvania, United States. He obtained his B.S. in chemistry from the University of Illinois in 1948 at age 20, and earned his PhD in chemistry from Northwestern University in 1954. He presented the first evidence that carbon dioxide produced by automobiles and factories was negatively affecting the Earth’s climate. In 1958 he began measuring carbon dioxide in the atmosphere with an instrument that he set up at a weather station on Mauna Loa, a dormant volcano in Hawaii. Over the next 47 years, he charted a steady increase of carbon dioxide levels and raised warnings about global warming and the dangers of continued reliance on fossil fuels. In 2002 Keeling was awarded the National Medal of Science. He died on June 20, 2005 in Hamilton, Montana, United States.