The Scripps O2 Program measures changes in atmospheric oxygen levels from air samples collected at stations around the world. This sampling network provides a global and hemispheric perspective on oxygen variability. The Scripps O2 Program is based at the Scripps Institution of Oceanography at La Jolla, California and is under the direction of Professor Ralph Keeling.
Oxygen levels are decreasing globally due to fossil-fuel burning. The changes are too small to have an impact on human health, but are of interest to the study of climate change and carbon dioxide. These plots show the atmospheric O2 concentration relative to the level around 1985. The observed downward trend amounts to 19 'per meg' per year. This corresponds to losing 19 O2 molecules out of every 1 million O2 molecules in the atmosphere each year.