The purpose of this site is to present data on changes in the atmospheric O2 abundance as measured by the Scripps O2 Program, and to provide context for understanding its importance.
The Scripps O2 Program was an outgrowth of Ph.D. thesis project of Ralph Keeling, which involved developing a method for measuring the O2 concentrations that was precise enough to track the miniscule variations in unpolluted air. Starting in 1989, regular sampling began at La Jolla. Over the next few years, the network grew to nine stations. A main goal is to quantify the yearly global O2 loss to improve understanding of the processes controlling the buildup of carbon dioxide. Since 2005, Ralph Keeling has also run the Scripps CO2 Program, initiated by his father, Charles D. Keeling, in 1956.
As CO2 rises, O2 falls, both driven largely by fossil-fuel usage. The O2 loss is very small compared to the large O2 background of the atmosphere, and therefore not an environmental concern by itself. What we gain from the O2 measurements is the ability to partition the sinks of CO2 between land and ocean: land plants take up CO2 by photosynthesis, which produces O2, whereas the oceans take up CO2 primarily by physical processes that have no effect on O2. By comparing the change in O2 with the change expected from fossil-fuel burning alone, we can gauge the strength of the land source for O2 and therefore also the land sink for CO2.
The measured trends in atmospheric O2 since 1989 confirm that O2 has been decreasing slightly slower than expected from fossil-fuel burning, and therefore that land plants have been producing small amounts of O2 and acting as a weak sink for CO2. This sink is occurring despite the direct human impacts on land, such as the clearing of land for agriculture, which by themselves would cause the land to be a CO2 source. Evidently, other processes on land are counteracting the direct human impacts. Continued measurements of O2 will help us track these processes into the future.
This material is based upon work supported by the National Science Foundation under Grant No. ATM-00330096 and National Oceanic and Atmospheric Administration under grant NA77RJ0453A. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or NOAA. These environmental data have not been formally disseminated by NOAA, and does not represent and should not be construed to represent any agency determination, view, or policy.