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Climate Resolve Talk with a Scientist: Riley Duren

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Riley Duren of NASA's Jet Propulsion Laboratory.

 
Riley Duren's job at NASA's Jet Propulsion Laboratory once involved scanning for Earth-like planets around other suns. Now he's turned his attention to watching the one we're on. "How do we keep Earth healthy? It's an important question," says Duren. As the principal investigator at JPL's Megacities Carbon Project, Duren is developing ways to measure and track greenhouse gas emissions from cities — the biggest human contributors to climate change — starting right here in Los Angeles. Duren talked to Climate Resolve about giving form and substance to normally invisible greenhouse gases.
 
Why megacities?
 
Riley Duren: Between 70 and 80 percent of carbon dioxide from fossil fuel combustion comes from urban areas and the power plants that supply them — and a significant amount of methane, too. It's where the people are, and where the most energy-intensive activities take place.
 
What are the goals of the Megacities Carbon Project?
 
RD: We're trying to answer basic questions like how carbon emissions from cities are changing over time, and why. Are emissions increasing because of accelerating development and urbanization — and/or are they decreasing because of efforts to mitigate or reduce greenhouse gas emissions? And can we provide information about those emissions in ways that help inform decisions by local stakeholders, including public and private sector?
 

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It turns out that while we have a really good grasp on how much carbon dioxide and methane is going in the atmosphere at a global scale, as you move to finer scales like an individual city, the uncertainty becomes quite large — just because we don't measure things directly at the city level.

What will cities be able to do with your insights?   

RD: Many cities around the world are serving as first responders to climate change. Mayors, city councils, regional governments are taking steps now, voluntary steps, to reduce their greenhouse gas emissions through various means. And so, by focusing our measurements of greenhouse gases on cities, we can help inform decisions by those cities to assess whether they're having the intended effect, and, if not, why?
 
What's the most exciting thing happening in your field?
 
RD: One of the most exciting things recently has been the application of different atmospheric monitoring methods to actually pinpoint the locations of methane sources in ways that we couldn't just two years ago.

Methane has some differences from CO2 in terms of how it manifests. Carbon dioxide we see from cars and from airplanes and from large stationary sources like power plants… Methane [can be] emitted by leaks in natural gas supply chains or oil production activities; methane is also released from landfills, from wastewater treatment facilities, and from dairies. And all of those sources are present in the LA Basin.

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We're approaching the capability now of being able to continuously monitor the methane emissions of the entire LA basin. So we can see how the emissions are changing on a daily, monthly, annual basis — but we can also detect hot spots, areas in the LA basin where there's more methane than before. And then, using aircraft with remote sensing instruments, we can fly overhead and actually map out those hot spot areas — detect individual methane sources and image the methane plumes that are coming out of the source, as small as a few meters across.
 
So we can go from the scale of the LA basin, 10,000 square kilometers, and zoom in to an area less than 10 meters across. And that's exciting because not only can we improve our understanding of the total methane emissions for LA, we can actually guide facility operators and owners to find leaks and correct them. And that has a lot of potential, I think, for enabling future mitigation.
 
Los Angeles recently experienced the worst single natural gas leak in U.S. history. What did it look like?
 
RD: The Aliso Canyon incident lasted for about four months last year; a number of research groups studied that while it was underway. Our efforts were primarily two-fold. One focus was on looking at the evolution of the emissions over time — before, during and after the event. Our other focus was using airborne and satellite observations of the plume to study in detail the mechanisms behind the leak — where was the plume coming from, and so forth.
 

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What gadgets do you use to see these invisible greenhouse gases?
 
RD: Everything but the kitchen sink! We'll use anything we can get our hands on that's useful. For the Megacities Project, we use everything from land, air, and space.
 
We have a network of commercial greenhouse gas analyzers located on radio towers and rooftops around the LA basin— 15 sites that operate 24/7. They sniff the air and use a technique called spectroscopy to measure greenhouse gases at those locations. We then use that data, together with atmospheric models — essentially the same kind of models used for weather forecasting, except we run them backwards in time — to try to estimate where the emissions of CO2 and methane are coming from across the basin. So that's the surface-based monitoring.

We also have instruments on aircraft. I mentioned the ones that we flew over Aliso Canyon. These are called imaging spectrometers, and the way to think about them is [as] a camera that can see many different wavelengths at once. We were able to produce images of plumes of methane gas and other gases that would otherwise be invisible, and we can do very fine scale imaging using those. But they're flown infrequently, and we can only fly them over certain areas. To date, we've surveyed only a small fraction of the LA basin with those aircraft.

And then the third approach we use are satellites. At the moment we're somewhat limited by the available state of the art. Current satellites that can measure methane and CO2 from space aren't designed to provide very high resolution — we can get a decent idea of the overall LA basin footprint, if you will, but it's difficult to see individual sources.
 
The exception to that was the Aliso Canyon event. That source was so strong, and the plume was so intense, we could see it from space. It's really not applicable everywhere else, because Aliso Canyon was unprecedented in its size. But it proved that we can scale these methods that we're using on aircraft to space. And we're working now on next generation satellites that will be able to do that for many sources around the world.
 
What kind of detail do all these instruments show?

RD: You can literally see patterns associated with traffic. You can see how CO2 emissions change by time of day, by day of week, by month of year, and how they change over time. You can see very strong point sources, like power plants and refineries. Similarly, you can see the footprints of large methane emitters, like landfills and wastewater treatment plants and dairies. Even dairies. We have those here in LA.
 
What's one of your favorite places in Los Angeles?
 
RD: One place that springs to mind are the mountains around Los Angeles, the San Gabriels. On clear days you have a panoramic view of the LA Basin, and in one vista you can see the ocean, you can see Catalina Island, you can see Palos Verdes, you can see all the way down to Orange County. And you can see a combination of urban sprawl and, surprisingly, green spaces, including places that still have a lot of trees. And then you can see the haze — you can see the atmosphere. That vista is very interesting, because it just shows how complex LA is.
 
A genie grants you two wishes that will help fight climate change. What do you ask for? The third wish is for anything you want.
 
RD: I would say that if I could have one wish to fight climate change, it would be improved knowledge and understanding of the earth as a system. You can't manage what you don’t measure and while we've made enormous strides in recent years, over the coming decades society will face increasing demands for better data about how the earth is changing in response to human activity and climate change. Informed decision-making requires a comprehensive, nimble and sustained "climate dashboard" for planet earth. That, in turn, will require detailed and long-term measurement of the earth’s land, atmosphere, and oceans. It's similar in concept to today’s operational weather services but would involve sustained monitoring of additional regions and processes as well as improving the skill of forecasts and projections.

Second: As an engineer, I would say that there needs to be more focus on technological innovation in carbon removal and the infrastructure to do it at scale. Reducing emissions through cleaner technology and conservation is absolutely necessary but probably not sufficient. That's because CO2 in particular has a very long lifetime and there’s already a substantial carbon burden in the atmosphere and oceans that will impact the earth’s climate and ecosystems for many years to come. So I think society also needs methods to safely and efficiently remove carbon from the atmosphere and oceans. The challenge here is time — the carbon mitigation and removal efforts will need to ramp up much faster than the history of growth in carbon emissions to avoid bad outcomes. 
 
For the third wish, sky's the limit.

I'd like some way to rewind the clock for the earth's biosphere to circa 1800 — before the industrial revolution began to literally transform the planet's landscape, atmospheric composition and energy balance. I realize we can't bring back extinct species, but there are ways to preserve and strengthen ecosystems and biodiversity. A healthy biosphere is essential both for managing carbon — for example, growing forests remove and store atmospheric carbon — and sustaining a wide range of societal needs. I also think most people resonate with the idea of preserving and restoring earth’s wild places because of their intrinsic value and beauty. I know from personal experience working on conservation projects that individuals can make a difference, but the scale of this challenge and competing pressures is daunting. If I could ask for [anything] it would be for our society to make understanding and improving biodiversity a top priority, and to do that today — not wait for future generations.
 

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