Lockdowns reduced air pollution from transport in 2020, but that helped methane concentrations rise, researchers said – Copyright AFP Sergei SUPINSKY
A mysterious rise in planet-warming atmospheric methane in 2020 despite Covid lockdowns that reduced many human-caused sources may be explained by a greater release from nature and, surprisingly, a reduction in air pollution, scientists have said. on Wednesday.
Methane stays in the atmosphere for only a fraction of the time as carbon dioxide, but it is much more efficient at trapping heat and is responsible for about 30 percent of the global rise in temperatures to date.
Released from the oil and gas, waste and agriculture sectors, as well as through biological processes in wetlands, the powerful greenhouse gas is a key target for efforts to curb global warming.
But a new study published in the journal Nature suggests that reducing methane may be an even bigger challenge – and more urgent – than is currently believed.
Researchers in China, France, the US and Norway found that efforts to reduce CO2 emissions and air pollution will affect the atmospheric process that removes methane from the air. That means the planet-warming gas will stick around longer and build up faster.
If the world wants to meet the challenge of keeping warming below 2 degrees Celsius since pre-industrial times, “we will have to act even faster and stronger to reduce methane,” said Philippe Ciais, co-leader of the research. at the French Laboratory of Climate and Environmental Sciences (LSCE).
The researchers zeroed in on the mystery of atmospheric methane concentrations in 2020, which had their biggest rise on record even as Covid-19 lockdowns saw carbon dioxide emissions plummet.
– ‘Bad news’ –
What they found is potentially two “bad news” for climate change, said co-author Marielle Saunois of (LSCE).
First, they looked at inventories to assess agricultural and fossil fuel methane emissions and found that human sources of methane actually fell slightly in 2020.
They then used ecosystem models to estimate that warmer and wetter conditions in parts of the northern hemisphere caused an increase in emissions from wetlands.
That confirms other research and is concerning because the more methane is released, the more warming potentially creates a feedback loop largely outside of human control.
But that’s only half the story, the researchers found.
The researchers also looked at changes in atmospheric chemistry, because this provides a “sink” for methane, effectively removing it from the air in a relatively short period by converting it to water and CO2 when it reacts with the hydroxyl (OH) radical.
These hydroxyl radicals are present in trace amounts and have a lifetime of less than a second, but they remove about 85 percent of methane from the atmosphere.
They are the “Pac-Man of the atmosphere,” said Ciais: “As soon as they see something they eat it and then they disappear.”
– ‘Dramatic’ –
The researchers simulated changes in OH using human sources of carbon monoxide, hydrocarbon, and nitrogen oxide emissions that together affect the production and loss of hydroxyl radicals in the atmosphere.
They found that OH concentrations fell by around 1.6 percent in 2020 from the previous year, largely due to a drop in nitrogen oxide (NOx) emissions caused by Covid lockdowns. Nitrogen oxide is emitted into the air primarily from the burning of fuel.
A 20 percent reduction in NOx could increase methane twice as fast, Cias told a news conference, adding: “This has surprised us a lot.”
The researchers said their study helps solve the puzzle of the rise in methane in the atmosphere by 2020.
But they acknowledged that more work would need to be done to answer the next mystery: why the rise in methane concentrations reached a new record in 2021.
Ciais said lower nitrogen oxide emissions from transportation in the United States and India, as well as continued low levels of air travel due to the pandemic may have played a role.
Euan Nisbet, a professor of Earth Sciences at Royal Holloway University who was not involved in the research, said the methane surge in 2020 was a “big shock.”
“Even more worrying is the rise in methane in 2021, this was after the major coronavirus lockdowns when the economy was picking up,” he told AFP.
“So far we don’t have detailed studies, but it seems that something very dramatic is happening.”