Aerial Scans Help Bust California’s Worst Methane Leakers

Small victories, to be sure, but they show some of the potential for more persistent, verifiable monitoring. “They looked at hundreds of thousands of these things. That’s the breakthrough. So now you have way better stats, and you’re not driving a truck around to wellpads and asking permission or whatever,” says Steven Wofsy, an atmospheric scientist at Harvard who also studies methane emissions. “They were able to detect large point sources where the operators didn’t know about them and mitigate them. I’m not aware that this has been done with an airborne sensor before.”

The scale of the study means its findings could have far-reaching effects. Even though Duren’s California Methane Survey looked only at focused point-source emissions, because it looked at so many and for so long, Duren’s team was able to conclude that by themselves those sources coughed out 500,000 metric tons of methane a year, give or take, and that just 10 percent of the emitters were responsible for 60 percent of the total. That confirms other research that has suggested that methane emissions have a “heavy tail,” which is to say, a small class of super-emitters are disproportionately responsible for the majority of gas in the air.

The team also found what it called “discrepancies” between its numbers and self-reported emissions from facilities like power plants in the Environmental Protection Agency’s Greenhouse Gas Reporting Program. More than half of the paper point-source emissions came from oil and gas tech and “manure management,” but those mostly don’t report to California’s GHGRP, according to the new paper. So current estimates for how much methane California emits in total could be lowballs.

“They sampled an enormous amount of infrastructure over numerous years,” says Adam Brandt, an environmental scientist at Stanford. “Also, they found that the super-emitter phenomenon holds across the whole state survey. Most of the emissions come from a small fraction of sources.” In other words, cap the top ten percent of methane emitters and you stop as much as a quarter of total methane emissions overall. Again: more bang for the buck.

That heavy tail seems to hold in California, full of agriculture and waste management with a little bit of oil and gas, and in the Four Corners area, with a lot more oil, gas, and coal infrastructure. It’ll take more research to figure out if the pattern holds in other regions—with even more sensitive instruments, maybe on higher-altitude aircraft or even satellites. “I’m really curious what this distribution of super-emitters would look like if you went to the East Coast, where you don’t have the same intensity of oil refineries and agriculture, but we do have a very different profile of landscape, age of infrastructure, and the distribution networks,” says Lucy Hutyra, a biogeochemist at Boston University. “I think area emissions will be a much bigger part of the rest of the country.”

But that doesn’t change the good news from California here. “It’s really amazing, as you see the plumes moving and the level of resolution and detail,” Hutyra says. “In terms of policy and science communication and just explaining what the problem is, this is astounding. I think they did a fantastic job.” When so much of the climate change fight often devolves into arguments over units and models, a clear visualization of wafting plumes of greenhouse gases can make it easier to understand the problem—and that’s the first step in fixing it.

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