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 CO2 record,” 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 CO2 emissions so far to be absorbed into the deep ocean and atmospheric CO2 to return to pre-industrial levels.
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 COVID19 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.”