In May, the Mauna Loa Observatory in Hawai'i recorded a seasonal peak in the atmospheric carbon dioxide (CO2) of 417.1 parts per million (ppm). This is the highest monthly reading of atmospheric CO2 ever recorded, 2.4ppm higher than the 2019 peak.
Annual CO2 level growth averaged 0.8 ppm in the 1960s, 1.6 ppm in the 1980s, and 2.0 ppm in the 2000s. Over the last decade, it has averaged a 2.4 ppm increase annually. The cause, undisputably, is human-made emissions from energy production, transportation, and industry. Global attempts to curb emissions have so far been limited.
“Progress in emissions reductions is not visible in the CO2 record,” Pieter Tans, a senior scientist with NOAA’s Global Monitoring Laboratory, said in a statement. “We continue to commit our planet – for centuries or longer – to more global heating, sea-level rise, and extreme weather events every year.”
Due to the Covid-19 global pandemic causing a global economic reduction across all sectors, the daily emissions across most human sectors were much smaller in 2020. This is not currently reflected in the measurement from Mauna Loa and may not make any difference in the long run. While the reduction was dramatic across March, April, and May, it is not a long-term trend, and with the easing of lockdown measures in attempts to restart economies around the world, it is unlikely to be carried forward.
“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.”
Measurements of CO2 concentration on Mauna Loa began in 1958, and from 1974 the National Oceanic and Atmospheric Administration (NOAA) and two other research institutions have made complementary, independent measurements. This is the longest unbroken measurement of carbon dioxide in the atmosphere.
The measurements were started by American scientist Charles David Keeling, who first realized that CO2 levels rose steadily year after year. He also noticed that the measurements showed a seasonal variation that peaked in May, before the increase in absorption of carbon dioxide from plants during the Boreal summer. The two effects produce a zig-zagging curve known as the Keeling Curve.