By Sherry Listgarten
The Other Greenhouse GasUploaded: Feb 17, 2019
One of the things that I think has given global warming a bad name (besides, well, the fact that it’s global warming), is that it can seem like everything causes global warming. We are told: No red meat! Remember to compost! Less dairy! Don’t waste food! And you begin to suspect that someone is pushing their own agenda. Is global warming going to make us gluten-free, too? I mean, at one level, we understand that when you burn things, it creates carbon dioxide, which insulates the planet, so things get warm, snow disappears, etc. That all kind of hangs together, and using less gas and coal makes sense. But what’s the deal with food and composting? There must be something else going on...
So this blog is an introduction to methane, the second biggest contributor to global warming (behind carbon dioxide), and what is behind many of these activities. I’m not going to footnote everything, but the sources in the notes are good references if you want to learn more.
What is methane? It is a very simple molecule (CH4), typically a gas, that is formed when organic matter decomposes in an oxygen-free environment. Think, for example, of a big marshy area, or the bottom of a compost pile. (1) Some of these environments are natural, and some of them are man-made. Here are some places where you’ll find a lot of methane:
- Wetlands. These are typically natural. You might think of a rice paddy, though, as a sort of man-made wetland.
- Landfills. Our buried trash releases a lot of methane, because it contains food, paper, yard waste, and other organic material. The oxygen is quickly depleted in landfills, and organic matter there decays over time to release methane.
- Geological formations. Methane generated deep in the earth from buried sediment forms large natural gas deposits. Sometimes it comes out through volcanoes, or leaks out through seeps. This is considered a natural emission of methane stored in the earth. But …
- Fossil fuel production and distribution systems. When we extract and distribute fossil fuels like natural gas, methane leaks out at various points of the process. The new kinds of extraction (e.g., fracking) are particularly leaky, and gas distribution infrastructure like pipes can get leaky as it ages. (2)
- Cow stomachs. This one is surprising! Cows (and other ruminants) have special stomachs (rumens) where microbes live and help digest the grasses and other tough fibers that the animals eat. This emits methane. The volume is pretty amazing: a typical cow generates over 60 gallons of methane gas every day. And there are over one billion(!) cows on Earth. It turns out they also each generate over 100 pounds of manure per day, which brings us to …
- Manure lagoons. Ugh, yes, they are really called that. Waste treatment (cow or human) generates methane, since it is often done in oxygen-free environments, like the big manure ponds at large feedlots. Izh.
So why do we care? Methane is a much more powerful greenhouse gas than CO2 -- about 86 times worse, when measured over a 20 year period. (3) That is why, even though there is much less of it in our atmosphere, it is the second largest man-made contributor to global warming, accounting for about 20% of greenhouse gas emissions. (4) The trends over the past ten years show a steady increase that we need to reverse.
Where does all the methane come from? Globally, about 40% comes from natural sources, mostly wetlands, and 60% from human-related activities: over half from livestock management and fossil fuel processing, but also things like rice cultivation and termite digestion. Locally, though, the story is pretty different, since we live in a more urban environment. If you look just at Santa Clara and San Mateo counties, 70% of our methane emissions come from landfills, and most of the rest (21%) from leaky gas infrastructure. This is why our cities are encouraging us to reduce food waste, recycle paper, and keep yard waste out of the trash.
Our two counties do not have much in the way of livestock, but the state of California has over half of its methane emissions from livestock digestion and management. You can see a breakdown of California’s methane emissions here (you’ll see “enteric fermentation”, which is livestock digestion). When you consider our indirect emissions -- emissions that are a result of our activities, but may not be emitted where we live -- you can understand the impact that our consumption of beef, dairy, and natural gas have on emissions in our state and beyond.
Reducing methane emissions can have many nice side-effects. These include improving safety and reducing air pollution when we fix gas leakages, reducing water pollution and odors when we improve livestock waste management, and improving soil composition by composting. There is much to be gained by working on this.
The next few blogs will take a closer look at some of these methane sources, in terms of technologies that are being applied to reduce emissions (e.g., “clean cows”), relevant public initiatives (e.g., gas line replacement), and actions we can take. I’d be interested to hear in the comments if there is anything you’d specifically like to learn more about.
References and notes
(1) There are two common ways methane is produced: (a) microbial or methanogenesis, in which microbes produce methane when they digest organic material; and (b) thermogenic, in which very high temperatures and pressures cause organic matter to decay. The first occurs in places as varied as wetlands and cow stomachs. The second type occurs deep in the earth.
(2) Natural gas is around 90% methane.
(3) Methane decays more quickly than CO2 (its lifetime is around 10 years), so if you look at it over a 100-year period, it is only about 34 times more powerful. This factor of 34 or so is the “equivalence” that is typically used when reporting emissions in CO2 equivalents. But right now many mitigation efforts are focused on a much shorter time frame than 100 years, so the impact of methane is often greater than what is reported.
(4) The title of this blog is a bit misleading, because there are many greenhouse gases besides carbon dioxide, including nitrous oxide, chlorofluorocarbons, and even water vapor. But this blog focuses on methane, since it is the second biggest contributor to anthropogenic climate change.
(5) If you are interested in learning more about our methane emissions, here are some good sources:
- NOAA’s Earth Systems Research Lab has a good overview here.
- The EPA has a high-level overview here.
- Detailed information about global methane emissions can be found at Global Carbon Atlas’s methane page.
- You can find out more about Bay Area methane emissions here (60-page PDF) and here (shorter, more focused article).
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