Keeling Curve

The Keeling Curve is a graph which plots the ongoing change in concentration of carbon dioxide in Earth's atmosphere since 1958. It is based on continuous measurements taken at the Mauna Loa Observatory in Hawaii that began under the supervision of Charles David Keeling. Keeling's measurements showed the first significant evidence of rapidly increasing carbon dioxide levels in the atmosphere. Many scientists credit Keeling's graph with first bringing the world's attention to the current increase of carbon dioxide in the atmosphere.

Charles David Keeling, of Scripps Institution of Oceanography at UC San Diego, was the first person to make frequent regular measurements of the atmospheric carbon dioxide (CO₂) concentration, taking readings at the South Pole and in Hawaii from 1958 onwards.

Measurements of carbon dioxide concentrations in the atmosphere had been taken prior to the Maunu Loa measurements, but on an ad-hoc basis across a variety of locations. Guy Stewart Callendar had shown a steady increase in concentrations since the 19th century. Keeling had perfected the measurement techniques and observed "strong diurnal behavior with steady values of about 310 ppm in the afternoon" at three locations: Big Sur near Monterey, the rain forests of Olympic Peninsula, and high mountain forests in Arizona. By measuring the ratio of two isotopes of carbon, Keeling attributed the diurnal change to respiration from local plants and soils, with afternoon values representative of the "free atmosphere". By 1960, Keeling and his group had determined that the measurement records from California, Antarctica, and Hawaii were long enough to see not just the diurnal and seasonal variations, but also a year-on-year increase that roughly matched the amount of fossil fuels burned per year. In the article that made him famous, Keeling observed, "at the South Pole the observed rate of increase is nearly that to be expected from the combustion of fossil fuel".