Remote detection technique helps quantify methane emitted by wildfires of 2020

New Delhi: Scientists have found, using a new remote method, massive amounts of methane, an immensely potent greenhouse gas to have been emitted by wildfires in the state of California, US.

For 2020, wildfires would have been the third biggest source of methane in the state, the scientists from University of California - Riverside (UCR) said in their study.

The study also calculated that the amount of methane from the top 20 fires in 2020 was more than seven times the average from wildfires in the previous 19 years, even while noting that wildfires emitting methane was nothing new.

The study by UCR, including their new remote methane detection technique, is published in the journal Atmospheric Chemistry and Physics.

Methane warms the planet 86 times more powerfully than carbon dioxide over the course of 20 years, the scientists said and stressed that it would be difficult for the state to reach its required cleaner air and climate goals without accounting for this source.

"Fires are getting bigger and more intense, and correspondingly, more emissions are coming from them," said UCR environmental sciences professor and study co-author Francesca Hopkins.

"Typically, these sources have been hard to measure, and it's questionable whether they're under our control. But we have to try," Hopkins said. "They're offsetting what we're trying to reduce." The researchers found nearly 20 gigagrams of methane emitted by 2020's Sequoia Lightning Fire Complex in the Sierra Nevadas, a mountain range in eastern California, using this remote technique. One gigagram is 1,000 metric tons.

This data, according to the researchers, matched measurements coming from European space agency satellite data, which took a more sweeping, global view of the burned areas, but were not capable of measuring methane in these conditions.

To measure emissions from the Sequoia Lightning Fire Complex, the research team used a remote sensing technique, which is safer for scientists, the researchers said.

This technique, they said, used the sun as a light source, rather than using a laser, as some instruments do. Gases in the plume absorb and then emit the sun's heat energy, allowing insight into the quantity of aerosols as well as carbon and methane that are present.

They also said that the technique was likely more accurate, since it captured an integrated plume from the fire that included different burning phases.

"The plume, or atmospheric column, is like a mixed signal of the whole fire, capturing the active as well as the smoldering phases," said Hopkins said. "That makes these measurements unique." Their technique allowed the team to safely measure an entire plume of the Sequoia Lightning Fire Complex gas and debris from about 65 kilometres away.

Conventionally, scientists measured such emissions by analysing wildlife air samples obtained via aircraft, a method that is costly and complicated to deploy, according to the researchers.

While 2020 was exceptional in terms of methane emissions, scientists expect more megafire years going forward with climate change.