NOAA scientists reported today (May 6, 2015) that global levels of carbon dioxide (CO2) – a heat-trapping gas in Earth’s atmosphere – have passed a significant milestone. These scientists say that, in March, 2015, the global monthly average for carbon dioxide concentration surpassed 400 parts per million (ppm).
That makes March, 2015 the first month since modern records have been kept that the entire globe broke 400 ppm in carbon dioxide levels. CO2 is currently measured at sites around the world, but the longest continuous record of atmospheric carbon dioxide began at Mauna Loa Observatory in Hawaii in 1958.
Using measurements of ancient carbon dioxide found in ice cores, scientists say they believe carbon dioxide has not reached 400 ppm in about 2 million years.
Pieter Tans is lead scientist of NOAA’s Global Greenhouse Gas Reference Network. Tans said:
It was only a matter of time that we would average 400 parts per million globally.
He said that C02 had passed the 400 ppm level for the first time in the Arctic in the spring of 2012, and at Mauna Loa in Hawaii in 2013. Tans said:
Reaching 400 parts per million as a global average is a significant milestone.
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 has occurred since 1980.
Carbon dioxide is a natural part of Earth’s atmosphere but the burning of fossil fuels sends excess amounts into the air and traps more of the sun’s heat.
The International Energy Agency reported on March 13, 2015 that the growth of global emissions from fossil fuel burning stalled in 2014, remaining at the same levels as 2013.
Stabilizing the rate of emissions is not enough to avert climate change, however. NOAA data show that the average growth rate of carbon dioxide concentration in the atmosphere from 2012 to 2014 was 2.25 ppm per year, the highest ever recorded over three consecutive years.
NOAA bases the global carbon dioxide concentration on air samples taken from 40 global sites. NOAA and partner scientists collect air samples in flasks while standing on cargo ship decks, on the shores of remote islands and at other locations around the world. It takes some time after each month’s end to compute this global average because samples are shipped from locations for analysis at NOAA’s Earth System Research Laboratory in Boulder, Colorado.
NOAA scientists expect that the global average will remain above 400 ppm through May, the time of year when global carbon dioxide concentrations peak due to natural cycles on top of the persistent rising greenhouse gases. Decaying plant matter and soil organisms give off carbon dioxide gas all year long, but the dormant period in plant growth allows the respiration of carbon dioxide to dominate during those months. Carbon dioxide levels drop back down as plants begin to bloom, using carbon dioxide for photosynthesis in late spring and summer.
James Butler, director of NOAA’s Global Monitoring Division, added that it would be difficult to reverse the increases of greenhouse gases which are driving increased atmospheric temperatures. He said:
Elimination of about 80 percent of fossil fuel emissions would essentially stop the rise in carbon dioxide in the atmosphere, but concentrations of carbon dioxide would not start decreasing until even further reductions are made and then it would only do so slowly.
Bottom line: NOAA scientists said on May 6, 2015 that, in March, the global monthly average for carbon dioxide concentration surpassed 400 parts per million. That’s the first month in modern record-keeping (which began in 1958) that the monthly average broke 400 ppm. Scientists say they believe the current level of carbon dioxide in Earth’s atmosphere is greater than it has been in 2 million years.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.