Methane concentrations in the atmosphere surged at a record rate in 2020, NOAA scientists announced yesterday.
The Earth-warming gas increased by 14.7 parts per billion, the largest annual rise since scientists started taking measurements in the 1980s.
It’s worrying news for the climate. Methane is a much more potent greenhouse gas than carbon dioxide, especially in the short term. Over a 20-year period, its climate-warming potential is more than 80 times stronger than CO2.
Recent increases in atmospheric methane have been a source of both concern and debate among scientists.
Methane steadily rose in the atmosphere between 1983, when scientists first started measuring it, until about 2000, when it temporarily leveled off. Around 2007, concentrations abruptly started climbing again—and they’ve been rising ever since.
Scientists have found it challenging to explain why.
There are many sources of methane around the globe, some natural and some human-made. They include carbon-rich wetlands, oil and gas operations, and methane-belching cows. Many of these sources are notoriously difficult to monitor. That’s made it hard for scientists to pinpoint which ones are most responsible for the latest spikes.
Still, recent research is slowly starting to reveal a clearer picture of what’s going on.
One study released this week in the journal Nature Geoscience suggests that wetlands may account for a bigger proportion of global methane emissions than scientists previously believed. Aquatic ecosystems could be responsible for as much as half of the world’s methane emissions.
That’s in contrast to other studies, which have suggested that direct human-caused emissions, such as the burning of fossil fuels, account for around 60% of all global methane emissions.
The new research reassesses methane emissions from 15 kinds of aquatic ecosystems, including rivers, lakes, mangrove forests and rice paddies. It takes a bottom-up approach, estimating emissions from each individual source and then adding them together.
The study suggests that aquatic ecosystems may account for a bigger share of global methane emissions than previous studies have indicated. They may be equally as important as direct human sources, or perhaps even more so.
There are still many uncertainties about methane emissions from aquatic environments. But if the new research is on the right track, it still doesn’t mean that all of these emissions are completely natural. The study notes that human activities strongly influence methane emissions from aquatic sources.
Human-made systems, like rice paddies or aquafarms, tend to produce higher emissions than natural ecosystems, like salt marshes or mangrove forests. Fertilizer and other agricultural waste can increase methane production when it runs off into nearby water systems. And other human disturbances, like dams, can also boost emissions.
At the same time, there’s growing evidence that methane from some direct human sources may be higher than previous estimates suggest. A number of recent studies have suggested that methane leaks are widespread in oil and gas infrastructure and that these emissions are often much larger than official estimates would indicate.
“Although increased fossil emissions may not be fully responsible for the recent growth in methane levels, reducing fossil methane emissions are an important step toward mitigating climate change,” NOAA scientist Ed Dlugokencky said in a statement accompanying the new 2020 measurements.
Last year’s methane jump is notable for more than one reason. Not only was it a record spike—it also happened despite the global shutdowns associated with the pandemic.
Studies suggest that global carbon dioxide emissions took a temporary dip in 2020 as a result of the pandemic. That said, CO2 levels still increased in the atmosphere last year, rising by about 2.6 parts per million. Even with the economic turndown, it was still the fifth-highest rate of increase on record.
Meanwhile, carbon dioxide levels are still marching higher in 2021. Just last week, NOAA announced that atmospheric CO2 had exceeded 420 parts per million for the first time since scientists started taking measurements in the 1950s.
Scientists believe that these levels are the highest the Earth has seen in several million years.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.