Global warming: Monthly average atmospheric CO2 levels exceed 400 ppm at remote sites for the first time on record

‘The path we’re on is foolish and dangerous and will lead to unacceptable changes’

By Bob Berwyn

SUMMIT COUNTY —Underscoring the inexorable increase in atmospheric carbon dioxide pollution, the National Oceanic and Atmospheric Administration reported today that average monthly concentrations of CO2 in the air around Barrow, Alaska reached 400 parts per million for the first time ever.

Carbon dioxide, emitted by fossil fuel combustion and other human activities, is the most significant greenhouse gas contributing to climate change.

The record-high readings came in April and May, at a time of year when CO2 levels are highest in the northern hemisphere just before plants start to absorb the gas as part of their growing cycle, but are worrisome nonetheless as an indicator of global CO2 levels.

“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 in Boulder. “We will likely see global average CO2 concentrations reach 400 ppm about 2016.”

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.

“It’s central evidence that the path we’re on is foolish and dangerous and will lead to unacceptable changes,” said Rocky Mountain Climate Organization director Stephen Saunders. “What’s little understood is that our current emissions are on the upper end of the spectrum,” said Saunders, whose organization assesses and publicizes potential global warming impacts in the greater Rocky Mountain Region.

Saunders said scientists usually look to the middle-of-the-road scenario when making projections about global warming impacts like sea level rise or precipitation changes. The current rate of emissions could lead to a much faster rate of warming, with significant impacts coming sooner than generally expected he said.

Together with other organizations and partners, Saunders’ organization has published reports showing how snowpack and streamflows could be affected by rising temperatures. Most recently, a report outlined how global warming may affect water supplies in key Colorado river basins.

NOAA said CO2 levels as six other remote high latitude sites also reached 400 ppm at lease once this spring, including monitoring stations in Canada, Iceland, Finland, Norway, and an island in the North Pacific.

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.

“Turning up the levels of greenhouse gases in our atmosphere is like turning up the dial on an electric blanket,” said Jim Butler, director of the ESRL Global Monitoring Division. “You know it will keep getting warmer, but you don’t know how quickly the temperature will rise, and it can take awhile for the blanket – or the atmosphere – to heat up.”


Scientists with ESRL’s Global Monitoring Division keep track of CO2 and other greenhouse gases in the atmosphere in two ways. First, the group coordinates an international cooperative flask sampling network in which scientists and volunteers at more than 60 sites around the world collect air samples weekly, shipping them back to Colorado for detailed laboratory analysis. Secondly, the group maintains six baseline observatories around the world, where staff collect flasks for analysis and also measure CO2 continuously, along with many other aspects of the atmosphere and solar radiation.

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.

This spring’s numbers are technically “preliminary,” and will not be finalized until next year, but rarely change more than 0.2 ppm, Tans said.  

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 YouTube at


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