Methane is a naturally occurring organic compound, but human activity has increased the amount of this potent greenhouse gas that goes into the atmosphere. Most of the methane that humans emit comes from natural gas, landfills, coal mining and manure management, but methane is almost everywhere and it comes from some surprising sources. Here are a few that you might not expect.


Hydroelectric dams: A risk and an opportunity

The 8,000 hydroelectric dams in the U.S. generate a huge amount of sustainable electricity, but they also produce methane. How? It's all part of the process to create a dam in the first place.


When a dam is built, the area behind the dam is flooded by water that can no longer travel where it used to flow. That leaves a potentially huge amount of vegetable matter — plants and trees that use to exist in the open air — rotting beneath the surface of the water. Rotting vegetation produces methane, and in normal situations that methane would escape into the atmosphere in incremental doses. But the rotting plants behind a dam store up their methane in the mud. When the supply of water lowers behind a dam, all of that stored-up methane can suddenly be released.


The amount of methane a dam could release varies depending on where and how the dam was built. A 2005 study published in the journal Mitigation and Adaptation Strategies for Global Change found that the Curuá-Una dam in Pará, Brazil, actually released three-and-a-half times more methane than an oil-based power plant generating the same amount of electricity. A study this year by a doctoral student at Washington State University found the mud behind one dam in Washington released 36 times more methane than normal when water levels were low.


But don't worry. Some scientists are already looking into this problem, suggesting the methane could be captured and turned into electricity.


The Arctic's growing methane problem

Just as methane is escaping from the mud behind dams, the gas is escaping from underneath Arctic ice and permafrost due to global warming. A study published this May in the journal Nature Geoscience found that methane gas, which had been trapped under the ice, is now escaping into the atmosphere as the Arctic region heats up. This, in turn, could speed up further warming.


The potential impact of all of this Arctic methane is still being studied, but it seems to be one of the bigger and most immediate dangers of climate change.


Ocean microbes: A new discovery in methane

As much as 4 percent of the planet's methane comes from the ocean, and a study published in August finally may have figured out how it gets there in the first place. According to scientists from the University of Illinois and Institute for Genomic Biology, the ocean-based microbe Nitrosopumilus maritimus produces methane through a complex biochemical process the researchers referred to as "weird chemistry." It was a totally unexpected discovery for two reasons. One, the researchers were actually looking for clues to create new antibiotics. And two, all other microbes known to produce methane can't tolerate oxygen, which is found in both the air and water.


Since N. maritimus happens to be one of the most abundant organisms on the planet, this could be a valuable discovery that will lead to a better understanding of the Earth's natural systems and climate change.


Composting: It has its downsides

Home or business composting is a great way to get rid of organic waste such as yard trimmings and food scraps and transform them into something useful. But it's not without its downside: The act of composting produces both carbon dioxide and methane. According to an EPA report (pdf), the amount of material composted in the U.S. from 1990 to 2010 increased 392 percent and methane emissions from composting have increased about the same percentage.


This shouldn't be a deterrent to composting, though. The amount of methane produced by composting is less than 1 percent what is produced by natural gas systems.


Oddly enough, the EPA estimates that composting levels have actually decreased by about 6 percent since 2008, so if you don't currently compost, you might want to consider starting. Compostable material you throw away will just end up emitting methane in landfills anyway, so you may as well do some good instead of sending your table scraps to the dump.


Rice: You're soaking in it

Rice may be one of the biggest food staples around the world, but its cultivation produced the third-highest levels of methane from all agricultural processes in 2010, according to an EPA report (pdf). 


Rice is grown in flooded fields, a situation that depletes the soil of oxygen. Soils that are anaerobic (lacking oxygen) allow the bacteria that produce methane from decomposing organic matter to thrive. Some of this methane then bubbles to the surface, but most of it is diffused back into the atmosphere through the rice plants themselves.


The cultivate manner matters, according to the EPA, which found that rice plants growing in especially deep water tend to have dead roots, which blocks the methane from diffusing through the plants. In addition, nitrate and sulfate fertilizers appear to inhibit the formation of methane. In the U.S., states such as Texas and Florida practice what is known as a ratoon (or second) rice crop using regrowth from the first crop which produces higher levels of emissions.


Rice production was up in most of the eight U.S. states that grow it from 2006 to 2010, resulting in a 45 percent increase in methane emissions.


Semiconductors: You're using one right now

Guess what: the device you're using to read this article was manufactured with the help of methane. Specifically, the semiconductors in computers and mobile devices are produced using several different methane gases, including trifluoromethane, perfluoromethane and perfluoroethane. Some of this gas escapes in the waste process. According to an EPA report (pdf), the total of all of these gases released in 2010 was the equivalent of 5.4 teragrams of carbon dioxide.


There's good news, though: The semiconductor industry has made consistent improvements to reduce waste and emissions, reducing them by 26 percent between 1999 and 2010.


No matter where you go, methane is a part of life on this planet. Understanding where it comes from can help us to reduce manmade emissions in the future and reduce the amount of greenhouse gases we are putting into the atmosphere.


Related story on MNN: What is methane and why should I care?


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