“The northern sites in our monitoring network tell us what is coming soon to the globe as a whole,” said Pieter Tans, an atmospheric scientist with NOAA’s Earth System Research Laboratory (ESRL) in Boulder, Colo. “We will likely see global average CO2 concentrations reach 400 ppm about 2016.”
Measurements at all those remote sites reflect background levels of CO2, influenced by long-term human emissions around the world, but not directly by emissions from a nearby population center. At other more locally influenced sites in NOAA’s network, such as Cape May, N.J., upwind cities influence CO2 concentrations, which have exceeded 400 ppm in spring for several years.
Average global levels of CO2 were 390.4 ppm in 2011, according to NOAA measurements, and will likely reach 400 ppm about 2016. Before the Industrial Revolution of the 1880s, global average CO2 was about 280 ppm.
Every year since 1959, when David Keeling of the Scripps Institution of Oceanography made the first accurate measurements of CO2 in the atmosphere, the concentration of the greenhouse gas has increased. In the early 1960s, it rose about 0.7 ppm per year. For the last decade, it has been rising at about 2 ppm per year. That observed increase, independent of the seasonal ups and downs described above, is due to the accelerating pace of emissions from human activities, particularly the burning of fossil fuels.
Carbon dioxide is not the only greenhouse gas. NOAA calculates the Annual Greenhouse Gas Index every year, which takes into account the heating effects of other gases that are emitted from human activities (e.g., methane, nitrous oxide, and chemicals called chlorofluorocarbons). When those gases are also considered, the global atmosphere reached a CO2 equivalent concentration of 400 ppm in 1985; and 450 ppm in 2003. Atmospheric CO2 levels are currently higher than they have been at any time during the last 800,000 years. Watch a NOAA Earth System Research Laboratory animation of carbon dioxide levels for the past 800,000 years on
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