Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder

Rise of Carbon Dioxide Unabated

Seasonal peak reaches 417 parts per million at Mauna Loa observatory



Atmospheric carbon dioxide measured at Mauna Loa Observatory reached a seasonal peak of 417.1 parts per million for 2020 in May, the highest monthly reading ever recorded, scientists from NOAA and Scripps Institution of Oceanography at the University of California San Diego announced today. 

This year’s peak value was 2.4 parts per million (ppm) higher than the 2019 peak of 414.7 ppm  recorded in May 2019. NOAA scientists reported a May average of 417.1 ppm. Scripps scientists reported an May average of 417.2 ppm. Monthly carbon dioxide (CO2) values at Mauna Loa first breached the 400 ppm threshold in 2014, and are now at levels not experienced by the atmosphere in several million years.

“Progress in emissions reductions is not visible in the COrecord,” said Pieter Tans, senior scientist with NOAA’s Global Monitoring Laboratory. ”We continue to commit our planet - for centuries or longer - to more global heating, sea level rise, and extreme weather events every year.” If humans were to suddenly stop emitting CO2, it would take thousands of years for our COemissions so far to be absorbed into the deep ocean and atmospheric CO2 to return to pre-industrial levels.

No apparent response to economic impact of coronavirus 

The rate of increase during 2020 does not appear to reflect reduction in pollution emissions due to the sharp, worldwide economic slowdown in response to the coronavirus pandemic. The reason is that the drop in emissions would need to be large enough to stand out from natural CO2 variability, caused by how plants and soils respond to seasonal and annual variations of temperature, humidity, soil moisture, etc. These natural variations are large, and so far the emissions reductions associated with COVID-19 do not stand out. If emissions reductions of 20 to 30 percent were sustained for six to 12 months, then the rate of increase of CO2 measured at Mauna Loa would be slowed. 

“People may be surprised to hear that the response to the coronavirus outbreak hasn’t done more to influence CO2 levels,” said geochemist Ralph Keeling, who runs the Scripps Oceanography program at Mauna Loa. “But the buildup of CO2 is a bit like trash in a landfill. As we keep emitting, it keeps piling up. The crisis has slowed emissions, but not enough to show up perceptibly at Mauna Loa. What will matter much more is the trajectory we take coming out of this situation.” 

Even though terrestrial plants and the global ocean absorb an amount of COequivalent to about half of the 40 billion tons of CO2 pollution emitted by humans each year, the rate of CO2 increase in the atmosphere has been steadily accelerating. In the 1960s, the annual growth averaged about 0.8 ppm per year. It doubled to 1.6 ppm per year in the 1980s and remained steady at 1.5 ppm per year in the 1990s. The average growth rate again surged to 2.0 ppm per year in the 2000s, and increased to 2.4 ppm per year during the last decade. “There is abundant and conclusive evidence that the acceleration is caused by increased emissions,” Tans said.

The longest unbroken record of CO2 measurements 

Charles David Keeling of Scripps Oceanography, located at the University of California San Diego, began on-site COmeasurements at a NOAA’s weather building on Mauna Loa in 1958, initiating what has become the longest unbroken record of CO2 measurements in the world. NOAA measurements began in 1974, and the two research institutions have made complementary, independent measurements ever since. CIRES researchers are involved at many stages, from shipping flasks around the world to air sampling and data analysis.


Read more at NOAA Research


CIRES is a partnership of NOAA and CU Boulder.