The Keeling curve is a graph showing the variation in concentration of atmospheric carbon dioxide since 1958. It shows that human activities are increasing the greenhouse effect with implications for global warming.

Charles David Keeling of the Scripps Institution of Oceanography was the first person to make frequent regular measurements of the atmospheric carbon dioxide (CO₂) concentration, taking readings atop Mauna Loa in Hawaii from 1958 onwards.

These measurements show a steady increase in mean atmospheric CO₂ concentration from about 315 parts per million by volume (ppmv) in 1958 to over 380 ppmv by the year 2006 ^*. This increase in atmospheric CO₂ is considered to be largely due to the combustion of fossil fuels, and has been accelerating in recent years, most likely due to increased fossil fuel combustion and the release of frozen CO₂ from melting ice caps and permafrost. This is supported by measurements of carbon dioxide concentration in ancient air bubbles trapped in polar ice cores, which show that mean atmospheric CO₂ concentration was between 275 and 280 ppmv for several thousand years but started rising sharply at the beginning of the nineteenth century. Since carbon dioxide is a greenhouse gas, this has implications for global warming.

The Keeling curve also shows a cyclic variation of about 5 ppmv in each year corresponding to the seasonal change in uptake of CO₂ by the world's land vegetation. Most of this vegetation is in the Northern hemisphere, since this is where the majority of the land is located. The level decreases from northern spring onwards as new plant growth takes carbon dioxide out of the atmosphere through photosynthesis and rises again in the northern fall as plants and leaves die off and decay to release the gas back into the atmosphere.

References

• Earthguide educational resource
• Carbon Dioxide Reasearch Group at the Scripps Institution of Oceanography

Atmosphere | Climate | Climate change | History of climate | Carbon_dioxide