Thinking About and Measuring Another Greenhouse Gas – Methane

            In my podcast series of “conversations on policy and practice,” whenever we have talked about global climate change, the focus has been on one very important greenhouse gas – carbon dioxide (CO2), linked primarily with the combustion of fossil fuels.  And nearly all of my guests have been economists, political scientists, legal scholars, policy makers, or industry leaders.  Only one guest has come from the academic world of the natural sciences, and that was early in 2020, when David Keith was with me.  In my most recent podcast, I finally break the mold, by hosting Daniel Jacob, the Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at Harvard, a world leader in the development of powerful inverse methods to infer from satellite observations of atmospheric concentrations reliable estimates of emissions of another very important greenhouse gas – methane. 

My conversation with Professor Jacob is featured in the latest episode of “Environmental Insights: Discussions on Policy and Practice from the Harvard Environmental Economics Program,” a podcast produced by the Harvard Environmental Economics Program. Our complete conversation is here.

In the podcast, Daniel Jacob explains how we should think about the relative importance of methane, compared with carbon dioxide (CO2), in regard to impacts on climate change.  He also provides insight about:  why there is great uncertainty regarding methane emissions; how technologies for detecting atmospheric concentrations of methane with satellites have been improving; and – importantly – how he and his research team use such satellite observations to infer spatially and temporally differentiated estimates of ground-based methane emissions.

Daniel explains that methane comes from a variety of sources: “There’s a natural source from wetlands. That’s about one third of the total source of methane right now. Two thirds are sources from human activity, and those sources include livestock, and in particular cattle, landfills, wastewater treatment plants, coal mines, oil and gas operations, and rice paddies.”

He goes on to explain that as a greenhouse gas, methane has impacts on climate similar to CO2, but there are very significant differences between the two.  First, methane is a vastly more potent greenhouse gas.  Its global warming potential is about 30 times that of CO2 over a 100-year period, and measured over a 20-year period that ratio grows to about 80 times the effect of a unit of CO2. The reason for the difference when measuring impacts over varying time scales is the significant difference in the atmospheric residence times of the two gases.

“Methane has a 10-year lifetime in the atmosphere because it gets oxidized.  CO2 is more complicated, but you can think of it as having about a 200-year lifetime,” Jacob explains. “What that means is that methane is responsible more for near term climate change, but also it means that acting on methane can give us a short-term response to climate. So, if we are trying to address climate change over the next decade or two, methane is a very powerful lever.”

From my perspective, Daniel Jacob’s work with satellite observations of methane is extremely important, because under the terms of the Paris Climate Agreement there is a need to accurately assess the national greenhouse gas (GHG) inventories that are reported by individual countries. Accurate measurements are also necessary under the terms of the new Global Methane Pledge, in which 119 countries have agreed to cut global emissions by 30 percent by 2030. But there has been tremendous uncertainty regarding the quantity and location of emissions.

As I noted above, Professor Jacob and his Harvard team use satellite observations of methane concentrations in specific locations at particular points in time, combined with additional information, to infer statistically, geographically and temporally differentiated emissions patterns.

“One of the things we can do uniquely from satellites is to look at recent changes in emissions, because the emission inventories that are coming out of individual countries are based on statistics that will typically be two or three years old,” Professor Jacob remarks. “But if we’re going to try to change the emissions rapidly, and to verify those changes in emissions, the only way that I can think of is to do it from satellites.”

Jacob recognizes that his satellite observations research could have substantive impacts on climate policy in the years ahead:  “What I would like to see is that we can contribute to continuous monitoring of emissions, to be able to detect changes in emissions, particularly if those are correctable, and point to the need for action. Say for example, if you have a flare that goes off, we should be able to see it from space, and then be able to take action on that.”

You can also see a brief video of Daniel Jacob talking about his research.

For all this and much more, I hope you will listen to my compete conversation with Daniel Jacob, which is the 39th episode in the Environmental Insights series, with future episodes scheduled to drop each month.  You can find a transcript of our conversation at the website of the Harvard Environmental Economics Program.  Previous episodes have featured conversations with:

“Environmental Insights” is hosted on SoundCloud, and is also available on iTunes, Pocket Casts, Spotify, and Stitcher.

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