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A massive gas leak in the Los Angeles area that was first announced in October is still leaking. The company that operates the storage facility where the leak happened says the leak could be capped as early as the end of the week.

Most of the leaking gas is the greenhouse gas methane, which is harmful to the environment. But how harmful is it?

Every week for the past few months, University of California, Davis researcher Stephen Conley has been flying a small, specially equipped plane into a huge plume of methane to measure the gas that has been leaking uncontrollably into the atmosphere.

Conley flies over natural gas storage facilities all the time. And he always sees small gas leaks. But when he was first asked to fly over this big leak in November, he was shocked by what he found.

"I'd never seen measurements like that before," he says. "So my first reaction was crap, what just happened? Did I hit too much turbulence and some laser got out of alignment? So my first question was that something was wrong ... ."

The readings were so high, he thought it was a mistake.

But when he landed he saw that two different instruments were each showing 50 or 60 parts of methane per million. The normal level in Los Angeles is around 2 parts per million.

In Conley's next two flights, the numbers he measured went up. Since late November, the levels have steadily been going down, but Conley says the amount of methane that's leaking out of the facility is enormous.

Once the company that runs the storage facility, Southern California Gas, thinks the well has been capped, Conley will run a test flight to confirm that the leak has stopped.

The company has depressurized the storage facility, which means it's leaking less gas than it was at the peak in November. But again, there's still a lot of gas.

Given those readings, we wanted to know how harmful all that methane is to the atmosphere in California and beyond.

We put that question to Rob Jackson, an environmental scientist at Stanford University.

"Methane is far more potent, molecule for molecule, than carbon dioxide is — the gas that people are used to thinking about in terms of climate change. On a 20-year time scale methane is 80 or 90 times more potent, molecule for molecule, than carbon dioxide. And even at a century time scale, it's 30 or 40 times. That's the reason that we care so much about methane in the atmosphere," he says.

So how big a deal is this gas leak?

"It really depends on the scale that you look. The amount of methane leaking out on a day-to-day basis is comparable to whole countries. If you look in Europe, for instance, countries like Belgium and Austria produce about this much methane on a day-to-day basis from human activities. So it's really big," Jackson says.

"If you look globally, you're not going to see a massive spike when you look back at 2015 and 2016. It's not that huge. It's a huge leak in human terms, but it's not big enough that it will affect the global methane cycle so much that this will be some kind of bellwether year. It's really pretty small in the global scheme of things.

"The issue is more one on a local scale, on a regional scale. It's also a symbol of our reliance on fossil fuels" at a time when California is trying to reduce greenhouse emissions, Jackson says.

"People have been spending millions and millions of dollars to dial back methane leaks around the U.S. and around the world. And one mistake like this comes along and can offset all of that, at least temporarily.

"Long term, those efforts to cut leaks really pay off," Jackson says. "But in the short term, this one mistake kind of offsets all of that. It's a little discouraging.

"The question is will this be some kind of turning point? Will this be a symbol that people use to drive a change, a transformation toward renewables? Or in six months will everybody have forgotten about what's happened? We don't know yet, but I think people will remember this."