Carbon dioxide at NOAA’s Mauna Loa Observatory reaches new milestone: Tops 400 ppm

NOAA: On May 9, the daily mean concentration of carbon dioxide in the atmosphere of Mauna Loa, Hawaii, surpassed 400 parts per million (ppm) for the first time since measurements began in 1958. Independent measurements made by both NOAA and the Scripps Institution of Oceanography have been approaching this level during the past week. It marks an important milestone because Mauna Loa, as the oldest continuous carbon dioxide (CO2) measurement station in the world, is the primary global benchmark site for monitoring the increase of this potent heat-trapping gas.

Carbon dioxide pumped into the atmosphere by fossil fuel burning and other human activities is the most significant greenhouse gas (GHG) contributing to climate change. Its concentration has increased every year since scientists started making measurements on the slopes of the Mauna Loa volcano more than five decades ago. The rate of increase has accelerated since the measurements started, from about 0.7 ppm per year in the late 1950s to 2.1 ppm per year during the last 10 years.

“That increase is not a surprise to scientists,” said NOAA senior scientist Pieter Tans, with the Global Monitoring Division of NOAA’s Earth System Research Laboratory in Boulder, Colo. “The evidence is conclusive that the strong growth of global CO2 emissions from the burning of coal, oil, and natural gas is driving the acceleration.”

It was researcher Charles David Keeling of the Scripps Institution of Oceanography, UC San Diego, who began measuring carbon dioxide at Mauna Loa in 1958, initiating now what is known as the “Keeling Curve.” His son, Ralph Keeling, also a geochemist at Scripps, has continued the Scripps measurement record since his father’s death in 2005.

“There’s no stopping CO2 from reaching 400 ppm,” said Ralph Keeling. “That’s now a done deal. But what happens from here on still matters to climate, and it’s still under our control. It mainly comes down to how much we continue to rely on fossil fuels for energy.”...

Photo of the Mauna Loa Observatory by NOAA