A new study believes that an underlying cause of the jump in methane levels recorded between 2019 and 2020 could be reduced nitric oxide emissions from road transportation, railways and airplanes as a result of Covid-19 lockdowns.
The researchers said that reduced transportation emissions led to lower levels of a chemical called the hydroxyl radical, which acts like a detergent to remove methane from the atmosphere.
William Collins, study co-author and professor of climate sciences at the University of Reading in the UK, said, “We saw a large rise in methane during the Covid-19 lockdowns so it was important to understand why this was happening as methane is a potent greenhouse gas responsible for a significant fraction of the current global warming.
“Our research shows that reduced travel during the pandemic played a part in this surge as fewer cars on the road and planes in the sky meant less of this methane-cleaning ‘detergent’ in the atmosphere.
“We can’t rely on this detergent as nitric oxide emissions need to be cut to improve air quality and human health. So this study shows an even stronger need to rapidly reduce emissions of methane from pipeline leaks and agriculture if we are to have any chance to meet the 1.5° climate goal.”
Until now, the causes of the 2020 surge in methane – second only to carbon dioxide as a driver of climate change – had been unclear. Previous research suggested the rise might partly have been the result of increased natural emissions from tropical wetlands.
A team led by a University of Edinburgh scientist used global atmospheric chemistry models to study how lockdown emission changes affected methane levels. These rose to a record 15 parts per billion (ppb) in 2020 – up from 9.7ppb in 2019. Previous studies estimate global nitrogen oxide, carbon monoxide and other transportation-related emissions fell by 10-20% in 2020.
The team’s findings suggest that, of the total 5.3ppb rise in methane growth rate in 2020, reduced transportation emissions led to a 2.9ppb increase. Reductions in nitrogen oxides led to a 4.8ppb increase that year, while reductions in carbon monoxide and other chemicals had the opposite effect, reducing methane growth by 1.9ppb.
Around 30% of the increase in methane in 2020 was caused by lower nitrogen oxide emissions from aviation, which fell by more than one-fifth globally.
To view the complete study published in the journal Atmospheric Chemistry and Physics, click here.