Despite a massive reduction in commuting and in many commercial activities during the early months of the pandemic, the amount of carbon dioxide in earth's atmosphere in May reached its highest level in modern history, a global indicator indicates.
Scientists from the US National Oceanic and Atmospheric Administration (NOAA) and the Scripps Institution of Oceanography at the University of California San Diego said the findings, based on the amount of carbon dioxide in the air at NOAA's weather station on Mauna Loa in Hawaii, was the highest since measurements began 63 years ago.
The measurement, called the Keeling Curve after Charles David Keeling, the scientist who began tracking carbon dioxide there in 1958, is a global benchmark for atmospheric CO2 levels.
Instruments perched on NOAA's mountaintop observatory recorded carbon dioxide at about 419 parts per million last month, more than the 417 parts per million in May 2020.
Carbon dioxide levels peak every May just before plant life in the northern hemisphere blossoms, sucking some of that CO2 out of the atmosphere and into flowers, leaves, seeds and stems.
The reprieve is temporary, though, because emissions of carbon dioxide from burning coal, oil and natural gas for transportation and electricity far exceed what plants can take in, pushing greenhouse gas levels higher.
Because carbon dioxide is a key driver of climate change, the findings show that reducing the use of fossil fuels, deforestation and other practises that lead to carbon emissions must be a top priority to avoid catastrophic consequences, Pieter Tans, a scientist with NOAA's Global Monitoring Laboratory, said in a report on the emissions.
"We are adding roughly 40 billion metric tonnes of CO2 pollution to the atmosphere per year," Tans wrote.
"That is a mountain of carbon that we dig up out of the earth, burn and release into the atmosphere as CO2 - year after year."
The amount of carbon dioxide in the air now is as much as it was about 4 million years ago, a time when sea level was 24 metres higher than it is today and the average temperature was 3C higher than it was before the Industrial Revolution, the report said.
Despite the pandemic lockdown, scientists were not able to see a drop in the overall amount of CO2 in the atmosphere partly because of wildfires, which also release carbon dioxide, as well as the natural behaviour of carbon dioxide in the atmosphere, the report said.
The carbon dioxide levels measured were not affected by the eruption of Hawaiian volcanoes, Tans said, adding the station is situated far enough from active volcanoes that measurements are not distorted and occasional plumes of carbon dioxide are removed from the data.