Ask Umbra: Is my compost pile contributing to climate change?
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Q. Composting has become a basic tenet of sustainable living, but it is also under debate: How irredeemable is its methane bi-production? Is there any way for homeowners to process compost so that methane production is limited or eliminated?
Santa Rosa, Calif.
A. Dearest Adriana,
Backyard composting sounds almost too good to be true, doesn’t it? You divert food scraps from the landfill and create an ultra-enriching soil booster that nourishes crops and gardens — and you do it all right out the back door so there’s no fuel used in shipping. So where’s the catch? Well, under certain conditions, decomposing matter does produce methane — a highly potent greenhouse gas 20 times worse for the climate than carbon dioxide. But here’s the unequivocally good news: Your compost pile doesn’t have to. With the right management, backyard compost can indeed be methane-free.
Here’s why: Methane forms under anaerobic, or zero-oxygen, conditions. Just like what’s found inside a landfill, you say? Exactly. Sealed inside landfills (where 96 percent of our orange peels and coffee grounds go, by the way), food waste slowly rots, spewing methane as it goes. Our trash heaps account for 17 percent of all U.S. methane emissions.
I should point out, Adriana, that not all that methane flies into the atmosphere to further warm the globe. We do have the technology to harvest and burn the gas to generate electricity, reducing it to water and carbon dioxide (which officials don’t count against us on the climate change scale because decomposing organic matter releases it naturally anyway). Happy face: Powering your fridge with methane means you’re not tapping a fossil fuel source. Sad face: These projects are limited in scope.
So back to us homeowners and what we can do: compost! The lovingly tended pile or bin in your backyard is, unlike a landfill, an aerobic (oxygenated) environment. And aerobic decomposition results in carbon dioxide (again, as part of the natural carbon cycle, a sort of climactic freebie), not methane. Nurturing that healthy, aerobic compost bin requires a little work on our part, but it’s not hard. And besides protecting the planet, the maintenance will keep your bin smelling, well, if not exactly fresh, at least not rotten-egg awful.
Here’s what you do: Make sure your bin is at least a cubic yard in size to ensure it’s big enough to build up to the proper temperature. Then fill it, tiramisu-style, with alternating layers of “browns” and “greens.” By browns, I mean dry, carbon-rich materials like cardboard, dry yard waste, potting soil, leaves, sawdust, and wood chips. These help aerate the pile, keeping it hospitable to the right kinds of decomposers. With greens, we’re talking wet, nitrogen-rich organics like food scraps and grass clippings. Aim for a brown-to-green ratio of three to one. And don’t include dairy, meat, bones, oils, or pet poop, as your compost won’t get hot enough to destroy any pathogens in them, and they tend to get stinky.
Then, every time you make a deposit, grab a shovel or pitchfork and give your pile a few turns or fluffs to infuse oxygen and discourage any anaerobic, methane-producing bacteria that might be hanging around looking for a new place to shack up. Alternately, you can set up your bin with pipes or a turner to accomplish the same thing. The bottom of the pile is often at the highest risk for low-oxygen conditions, so you can also set the bin on a wooden pallet, a pile of wood chips, or a layer of criss-crossed sticks to promote airflow.
And really, that’s it. Composting takes a little trial and error to get right, but that’s essentially what it takes to run a tight, methane-free ship. The steps are simple, yet classically important. You think the fact that a pitchfork has a starring role in America’s most iconic artwork is a mere coincidence?