Earth’s carbon dioxide levels hit record high in May despite coronavirus-related emissions drop, analysis shows
Monthly carbon dioxide values first breached the 400 ppm threshold in 2014, and are now at levels not experienced by the atmosphere in several million years
Lockdowns and economic slowdown during the coronavirus pandemic have had no visible impact on the amount of carbon dioxide in the Earth’s atmosphere. Atmospheric carbon dioxide continued its rapid rise this year, and hit a record high of 417.1 parts per million (ppm) in May 2020, up from 414.7 ppm in May 2019, according to data published by the National Oceanic and Atmospheric Administration (NOAA) and Scripps Institution of Oceanography at the University of California San Diego.
“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. 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,” said the analysis. While NOAA scientists reported a May average of 417.1 ppm, Scripps scientists reported a May average of 417.2 ppm. The two datasets, however, tell the same story: increasing levels of greenhouse gases are heating Earth’s surface, melting ice, and accelerating sea-level rise.
“People may be surprised to hear that the response to the coronavirus outbreak hasn’t done more to influence carbon dioxide levels. But the buildup of carbon dioxide 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,” said geochemist Ralph Keeling, who runs the Scripps Oceanography program at Mauna Loa, in the report.
The 2019 peak value was 3.5 ppm higher than the 411.2 ppm peak in May 2018 and marked the second-highest annual jump on record. Monthly carbon dioxide 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, say experts. A recent study had said that due to the worldwide lockdown, daily emissions had decreased by 17% -- or 17 million tonnes of carbon dioxide -- globally during the peak of the confinement measures in early April compared to mean daily levels in 2019, dropping to levels last observed in 2006. In individual countries, emissions decreased by 26% on average at the peak of their confinement, said the study published in Nature Climate Change.
However, NOAA scientists said that the progress in emissions reductions is not visible in the carbon dioxide record. They said if humans were to suddenly stop emitting carbon dioxide, it would take thousands of years for carbon dioxide emissions so far to be absorbed into the deep ocean and atmospheric carbon dioxide to return to pre-industrial levels. The team explained that the drop in worldwide emissions due to the Covid-19 pandemic fails to cancel out the large natural variations in carbon emissions caused by how plants and soils respond to seasonal and annual variations of temperature, humidity, and soil moisture, among others. “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% were sustained for six to 12 months, then the rate of increase of carbon dioxide measured at Mauna Loa would be slowed,” said the report.
The research team further said that even though terrestrial plants and the global ocean absorb an amount of carbon dioxide equivalent to about half of the 40 billion tons of carbon dioxide pollution emitted by humans each year, the rate of carbon dioxide 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, shows analysis.
The carbon dioxide data on Mauna Loa constitute the longest record of direct measurements of carbon dioxide in the atmosphere. Charles David Keeling of the Scripps Institution of Oceanography began measurements in 1958 at the NOAA weather station. NOAA started its own carbon dioxide measurements in May of 1974, and they have run in parallel with those made by Scripps since then. According to experts, it is critically important to have these accurate, long-term measurements of carbon dioxide to understand how quickly fossil fuel pollution is changing the climate.
The highest monthly mean carbon dioxide value of the year occurs in May, just before plants start to remove large amounts of the greenhouse gas from the atmosphere during the northern hemisphere growing season. In the northern fall, winter and early spring, plants, and soils give off carbon dioxide, which causes levels to rise through May. Charles Keeling was the first to observe this seasonal rise and subsequent fall in carbon dioxide levels embedded within annual increases, a cycle now known as the Keeling Curve.