The planet has hit a new high. This March, our monthly average carbon dioxide concentrations surpassed 400 parts per million globally. It’s the first time this has happened since we started tracking the greenhouse gas in the atmosphere, according to figures released by the National Oceanic and Atmospheric Administration (NOAA) this week.
“It was only a matter of time that we would average 400 parts per million globally,” Pieter Tans of NOAA’s Global Greenhouse Gas Reference Network says in a news release. “This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120 parts per million since pre-industrial times.” Half of that rise came about after 1980.
The first report of 400 ppm came when all of the network’s Arctic sites reached that value back in the spring of 2012. The next year, the Mauna Loa Observatory crossed that same threshold for the first time. “Reaching 400 parts per million as a global average is a significant milestone,” Tans adds. In fact, the last time it was this high, our species hadn’t evolved yet, the Guardian reports.
For comparison, in March of 2014, the global CO2 was 398.10 ppm. This March, it was 400.83 ppm, according to preliminary data from NOAA. And global concentrations are expected to stay above 400 ppm through May: While decaying plant matter and soil microbes give off CO2 all year long, a dormant period in plant growth means respiration of CO2 is heightened during these months. Levels drop as plants start to bloom late in the spring and summertime, since CO2 is used during photosynthesis.
These CO2 concentrations are based on air samples collected in flasks by scientists in 40 sites around the planet— including the decks of ships (such as the MV Pacific Celebes pictured to the right above) and the shores of faraway islands (such as Easter Island pictured below). “We choose to sample at these sites because the atmosphere itself serves to average out gas concentrations that are being affected by human and natural forces,” NOAA’s Ed Dlugokencky explains. “At these remote sites we get a better global average.” The samples are then shipped to NOAA’s Earth System Research Laboratory in Boulder, Colorado. (That’s why there’s a bit of a time lag.)
Global emissions from burning fossil fuels stalled in 2014, remaining at 2013 levels, the International Energy Agency reported earlier this year. But unfortunately, this stabilization isn’t enough. The growth rate of CO2 concentrations in the atmosphere from 2012 to 2014 averaged 2.25 ppm per year, according to NOAA. That’s the highest ever recorded during three consecutive years.
Reversing greenhouse gas increases will be difficult, to say the least. “Elimination of about 80 percent of fossil fuel emissions would essentially stop the rise in carbon dioxide in the atmosphere,” says James Butler of NOAA’s Global Monitoring Division. “But concentrations of carbon dioxide would not start decreasing until even further reductions are made and then it would only do so slowly.”