Two NASA Studies Find Lower Methane Emissions in Los Angeles Region

Researchers found that emissions of the powerful greenhouse gas dropped for several years near the nation’s second-largest metropolitan area.

Two recent studies by researchers at NASA’s Jet Propulsion Laboratory in Southern California used contrasting approaches to measure drops in human-caused emissions of the potent greenhouse gas methane in recent years in the Los Angeles region.

In the first study, published in February in Environmental Research Letters, scientists analyzed data from ground-based sensors scattered around four counties in densely populated Southern California: Los Angeles, Orange, San Bernardino, and Riverside. They found emissions fell by about 7% between 2015 and 2020 – a reduction of 33 million pounds (15 million kilograms) of methane released per year.

The second study, published in March in Environmental Research Communications, compared emissions from a belt of oil refineries across the South Bay area of Los Angeles during the first summer of the COVID-19 pandemic to those observed three years earlier. Using data from a NASA airborne instrument, researchers saw that most of the facilities they identified as methane sources in the earlier campaign were no longer emitting the greenhouse gas, leading to a 73% reduction in measured emissions. While such a reduction around COVID disruptions was not necessarily surprising, the result was important for demonstrating scientists’ ability to track point sources of methane.

Methane has a much shorter atmospheric lifespan than carbon dioxide – around 12 years, compared to centuries for carbon dioxide – but it absorbs much more energy while it exists in the atmosphere. Therefore, reducing human-caused emissions of the gas is a particularly effective way to make significant, short-term impacts on global climate change.

“These papers demonstrate that methane reductions are not only possible, they’re measurable through persistent monitoring,” said Andrew Thorpe, lead author of the COVID-period study and a JPL research technologist.

That two studies could use different techniques to identify and quantify emissions trends is crucial for generating confidence in the conclusions drawn from methane observations, added Vineet Yadav, a JPL data scientist and lead author of the first paper.