PBS高端访谈:美国科学家测量空气中的甲烷气体（在线收听）

JUDY WOODRUFF: We heard in the last segment a little about natural gas produced in the U.S. It turns out it is a big factor in the overall growth of energy production in this country over the past decade. But producing and transporting that gas releases methane, a potent greenhouse gas that's gotten a lot less attention when it comes to climate change. Miles O'Brien reports on how California is zeroing in on this issue. It's part of our weekly segment on the Leading Edge of science, medicine and technology.

MAN: This is Honor Rancho. This is about 10 clicks north or so.

MILES O'BRIEN: It's time for a preflight briefing at Burbank Airport.

MAN: We're going to get plenty of data over the over the site.

MILES O'BRIEN: I'm flying with a team from NASA's Jet Propulsion Laboratory. A place that specializes in exploring distant planets today is focused on our own. They're taking flight over Southern California, hunting one of the most potent greenhouse gases of all, methane. It accounts for one-fifth of the global warming we are experiencing now.

RILEY DUREN, Jet Propulsion Laboratory: You can't manage what you don't measure.

MILES O'BRIEN: Riley Duren is the chief systems engineer for JPL's Earth Science Directorate. He and technologist Andrew Thorpe are using a state-of-the-art infrared imaging spectrometer to find plumes of methane invisible to the human eye. Nationally, the EPA estimates about one-third of methane emissions come from oil and gas production, another third from the methane created by the belches and manure of livestock, and about 16 percent from organic waste dumped in landfills. So, today, we are flying over fertile methane territory. There are 200,000 oil and gas wells, almost 2,000 dairy farms and hundreds of landfills in California.

RILEY DUREN: Think of it as a baseline medical exam. No one has done the first methane assessment of the state of California, and maybe this ought to happen every year.

MILES O'BRIEN: California is funding the flights to find and stop methane leaks. There is good reason to focus on methane in the fight against climate change. Lasting only a decade or so, it is shorter-lived than carbon dioxide, which persists for a century or more. But during its lifespan, methane is about 85 times more potent at trapping heat than carbon dioxide.

RILEY DUREN: What the state is trying to do is to get an initial assessment of how many strong methane sources are there in the state, where they're located, how much are they emitting?

MILES O'BRIEN: In 2016, researchers from Harvard used satellite and ground observations to determine methane emissions steadily increased in the past decade, and they concluded the EPA is underestimating methane leaks from all sources by 30 to 50 percent. More recently, the Environmental Defense Fund published a study in the journal "Science" concluding the EPA is underestimating methane leak in oil and gas production by about 60 percent. The first step to plugging these methane leaks is pinpointing them. On flights like these, JPL is using the Airborne Visible/Infrared Imaging Spectrometer, or AVIRIS, to do just that. It can detect gases by analyzing the spectrum of light transmitted by the atmosphere. The spectrum of methane is like a fingerprint. Like every other gas, methane absorbs a unique slice of the full spectrum coming from the sun.

RILEY DUREN: This is the most active producing part of the state right now, is this county that we're heading towards. So, when you add it all up, there are literally millions of potential emission sources in the area that we're mapping.

MILES O'BRIEN: The AVIRIS team routinely shares what it learns with those emitters, including the operators of the huge Sunshine Canyon landfill in Los Angeles. On an earlier flight, the team saw a huge plume of methane billowing from areas where the topsoil had been stripped away in advance to make space for more dumping. So, the landfill changed its routine, keeping the topsoil in place until just before the trash is dumped, greatly reducing methane emissions. AVIRIS was also deployed to capture images of a massive natural gas blowout. It happened at a Southern California gas company storage facility near Porter Ranch. It was captured on video using an infrared camera as well. It began in October 2015 and lasted four months. Nearly 100,000 tons of methane were released, about 5 percent of the gas that SoCal delivers annually, the worst natural gas leak in U.S. history.

DEANNA HAINES, Southern California Gas Company: It was something that was disheartening for all of us.

MILES O'BRIEN: Deanna Haines is director of gas engineering for SoCal. It is the largest gas distribution company in the United States, maintaining over 100,000 miles of gas mains.

DEANNA HAINES: It didn't negate all the good that we have been doing over the last decades to mitigate methane, but it certainly, it didn't feel great.

MILES O'BRIEN: I met her at the training center they call Situation City. Here, they practice maintenance and repair techniques and test new technology. The tried-and-true method for finding leaks is the human nose, which can detect the sulfur smell that the company adds to the odorless methane, also called natural gas. But they augment that with some technology, fixed sensors at strategic locations, a van that can detect even very tiny amounts of methane, infrared cameras to inspect pipes, and a drone outfitted with a small laser. They say the priority is avoiding natural gas explosions, and it is not cost-effective to fix every leak.

DEANNA HAINES: There are some leaks that it's been either very difficult to go after, it costs a lot of money to go after, but, more importantly, we need to prioritize safety first. When we find leaks, we need to fix them in a reasonable amount of time.

MILES O'BRIEN: In the aircraft, AVIRIS has spotted methane leaks in SoCal pipelines that the company has repaired, proof there is the value to this type of survey. But it is, after all, just a narrow snapshot of a global problem. So the team is proposing a similar instrument be launched into space. They think methane mitigation is a good place to start stemming greenhouse gasses.

RILEY DUREN: CO2 emissions have to be addressed. But CO2 emissions involve economy-wide processes. They involve our power generation, our transportation, like the airplane we're flying on right now. And those are going to require economy-wide shifts in technology. And it's happening, but it may take a long time. Methane in the meantime has potentially near-term climate benefits over the next few decades.

BARACK OBAMA, Former President of the United States: 2014 was the planet's warmest year on record.

MILES O'BRIEN: During the Obama administration, regulators were enticed by that argument. The Department of Interior and the Environmental Protection Agency had imposed rules forcing gas and oil producers to detect and repair methane leaks.

DONALD TRUMP, President of the United States: With today's executive action, I am taking historic steps to lift the restrictions on American energy.

MILES O'BRIEN: But the Trump administration has tried to reverse all of that, facing pressure from industry, which insists the regulations impose too great a financial burden. But this might seem surprising. It's just a little odd to me that a company would just say, oh, I don't need even want to know how much of my product I'm losing.

DEANNA HAINES: Yes, it seems odd to me too. It's like it's nonintuitive. If you're in any business, you want to keep your product intact.

You don't want to lose it.

MILES O'BRIEN: Congress and the federal courts have offered contradictory votes and rulings on the Obama era rules. The net effect, much of the regulations remain in place, for now. But there is no scientific debate that reducing the amount of methane in the atmosphere can make a significant dent in greenhouse gases. In the seemingly insurmountable fight against climate change, methane may be the low-hanging fruit.

For the "PBS NewsHour," I'm Miles O'Brien in Burbank, California.

这是荣耀Rancho。大概北向10点。

迈尔斯·奥布赖恩：现在是伯班克机场进行飞行前注意事项播报的时候了。

男人：我们将从那里获得大量数据。

迈尔斯·奥布赖恩：我与美国宇航局喷气推进实验室的成员同机飞行。今天，这个专于探索遥远星球的机构将把焦点放在我们自己身上。他们正在南加州上空飞行，寻找最强大的温室气体之一——甲烷。在我们现在正在经历的全球变暖中，它的贡献占到五分之一。

赖利·杜伦，喷气推进实验室：你不测量，就无法管理。

迈尔斯·奥布赖恩：赖利·杜伦是喷气推进实验室地球科学部的首席系统工程师。他和技术专家安德鲁·索普正在使用最先进的红外成像光谱仪来探测人眼看不见的甲烷。在全国范围内，美国环境保护署估计约有三分之一的甲烷排放来自于石油和天然气生产，另有三分之一则来自于畜栏的打嗝和粪便，而大约16％来自垃圾填埋场倾倒的有机废物。所以，今天我们正在飞越一片肥沃的甲烷之土。加利福尼亚州有20万个油气井，近2,000个奶牛场和数百个垃圾填埋场。

赖利·杜伦：我们将其视为一个基线体检。此前从没有人对加利福尼亚州进行过甲烷评估，而也许这种评估每年都应该去做。

迈尔斯·奥布赖恩：加利福尼亚州正在资助一些航班，寻找并阻止甲烷泄漏。在抗击气候变化的斗争中，我们有充分的理由关注甲烷。甲烷问题持续仅有十年左右，相比二氧化碳，时间尚短，二氧化碳问题则持续了一个世纪或更长时间。但在使用甲烷期间，甲烷在捕获热量方面比二氧化碳强大约85倍。

赖利·杜伦：加利福尼亚州试图做的是，初步评估该州有多少强甲烷源，它们位于何处，它们排放多少？

迈尔斯·奥布赖恩：2016年，哈佛大学的研究人员们，通过卫星以及地面观测，确定甲烷排放在过去十年中稳步增加，他们得出的结论是，针对所有甲烷来源，美国环境保护署对泄漏率低估了30％至50％。最近，美国环保协会在《科学》杂志上发表了一项研究，其结论是美国环境保护署低估了石油和天然气生产中的甲烷泄漏，其低估率约达60％。堵塞这些甲烷泄漏的第一步是确定它们的位置。在像这样的航班上，喷气推进实验室正在使用机载可见光/红外成像光谱仪（AVIRIS）来实现这一点。它可以通过分析大气传输光谱来检测气体。甲烷的光谱就像一个指纹。与其他所有气体一样，甲烷会吸收来自太阳的全部光谱。

赖利·杜伦：这是现在该州最活跃的泄露部分，我们正在前往这个县。因此，当你整体来看时，我们正在绘制这个区域中，数百万个潜在的排放源。

迈尔斯·奥布赖恩：机载可见光/红外成像光谱仪团队经常会将他们对排放源的了解分享出来，包括洛杉矶巨大的阳光峡谷垃圾填埋场的操作员们。在早些时候的飞行中，该团队看到了一大团甲烷，这些甲烷从预先剥离表土的地方滚滚而来，剥离表土的目的是为更多的倾倒腾出空间。那么，这个垃圾填埋场一改常规，垃圾倾倒之前，不进行表土剥离，这种做法大大减少了甲烷的排放。机载可见光/红外成像光谱仪还用于捕获大规模天然气井喷的图像。这种应用见于波特牧场附近南加州天然气公司的储存设施。它也是使用红外摄像头拍摄的视频。这场拍摄始于2015年10月，历时四个月。近10万吨甲烷遭到泄露，是南加州天然气公司每年交付天然气总量的约5％，是美国历史上最严重的天然气泄漏。

迪安娜·海恩斯，南加州天然气公司：这对我们所有人来说都是令人沮丧的。

迈尔斯·奥布赖恩：迪安娜·海恩斯是南加州天然气公司的天然气工程总监。它是美国最大的天然气配送公司，拥有超过100,000英里的燃气总管。

迪安娜·海恩斯：这并没有否定我们过去几十年来为减少甲烷所做的全部贡献，但它肯定 - 它感觉不太好。

迈尔斯·奥布赖恩：我在训培训中心遇到了她，他们称之为情境城。他们在这里练习维护和修理技术并完成新技术测试。发现泄漏，我们有一种经过验证的方法就是利用人的鼻子，它可以检测公司添加到无味甲烷（也称为天然气）中的硫磺气味。但它们通过一些技术，在战略位置布设固定传感器，还有可以检测极微量甲烷的货车，用于检查管道的红外摄像机以及配备小型激光器的无人机来加强检测效果。他们说他们优先考虑的问题是避免天然气爆炸，对泄漏点进行逐个修复不符合成本效益。

迪安娜·海恩斯：有一些泄漏，要么很难追踪，要么要花很多钱，才能追踪得到，但更重要的是，我们需要优先考虑安全性。当我们发现泄漏时，我们需要在合理的时间内修复它们。

迈尔斯·奥布赖恩：在飞机上，机载可见光/红外成像光谱仪已经发现，南加州天然气公司已修复了其管道中的甲烷泄漏，证明此类调查具有价值。但毕竟，这只是全球问题中一个范围狭小的快照。因此，该团队正在提议将类似的仪器发射到太空。他们认为减少甲烷是开始遏制温室气体排放的一个好的开端。

赖利·杜伦：二氧化碳排放问题必须得到解决。但二氧化碳排放问题涉及整个经济过程。它们涉及到我们的发电，我们的运输，就像我们现在乘坐的飞机一样。这些将需要整个经济的技术转变。这种转变正在发生，但可能需要很长时间。与此同时，甲烷在未来几十年内具有潜在的近期气候效益。

巴拉克·奥巴马，美国前总统：2014年是这个星球上有史以来最温暖的一年。

迈尔斯·奥布赖恩：在奥巴马执政期间，监管机构被这一论点所吸引。其内政部和环境保护局制定了强制规定，迫使天然气和石油生产商检测和修复甲烷泄漏。

唐纳德·特鲁普，美国总统：在今天的行政行动中，我正采取历史性措施解除对美国能源的限制。

迈尔斯·奥布赖恩：但特朗普政府面临来自行业的压力，试图扭转这一切，该行业坚持认为，法规给它们施加了太大的财务负担。但这似乎令人惊讶。对我来说，公司只会说，哦，我甚至不想知道我失去了多少产品，这有点奇怪。

迪安娜·海恩斯：是的，这对我来说似乎很奇怪。这就像它不直观。如果您从事任何业务，您希望保持产品的完整性。您不想失去它。

迈尔斯·奥布赖恩：国会和联邦法院对奥巴马时代的法规做出了相互矛盾的投票和裁决。目前，净效应，大部分法规仍然存在。但是没有科学争论，认为减少大气中甲烷的含量会对温室气体影响巨大。在应对气候变化的斗争中，我们看似无法克服，而甲烷可能是容易摘到的果子。“新闻一小时”，我是来自加州伯班克的迈尔斯·奥布赖恩。