Dear Umbra,

I was explaining to my neighbor (who doesn’t even recycle) why he shouldn’t throw out a bag of leaves with his trash. Just to clarify, he asked what to do with it. I explained composting; he doesn’t want to. I explained the energy expended in transporting his leaves and that landfills emit greenhouse gases as the materials break down. It got me thinking. Why is it better for my kitchen scraps and leaves, etc., to break down in my compost pile vs. in a landfill? Doesn’t it emit greenhouse gases at home?

Continually composting,
Sue R.
St. Paul, Minn.

Dearest Sue,

Maybe you should write in again with a verbatim account of how you approached your neighbor, so that we all can understand how to have a civil, neighborly, curbside discussion about waste disposal. Not an easy thing to do. What was the end result, by the way? Did he throw the leaves out?

Like a good neighbor, compost is there.

There are many reasons, including those you have already mentioned, for keeping organic wastes out of the solid waste stream. Solid waste goes to either a landfill or an incinerator, each costly and polluting in its own way, which is why many cities now invest in curbside yard waste and even food waste pickup. The major global warming issues with organic matter in landfills include the fuel-using machines on the road and at the site. In a landfill there is some anaerobic decomposition, which releases CO2, methane, and nitrous oxides. In 2001, the IPCC told us that U.S. landfill methane emissions were higher than agricultural methane emissions and just barely lower than energy-related methane emissions. Step aside, cows — our garbage is worse than your burps and your pies.

To compost at home is to move toward a closed system of inputs and outputs, where less goes out and less is bought or brought in. In addition to reducing the general solid waste burden on your community, your organic discards don’t emit any transportation-related emissions.

Studies on the greenhouse-gas emissions of compost itself have largely focused on commercial composting operations (understandably). The IPCC again, referring to commercial systems, says food waste composting results in “significantly lower” emissions than landfilling, whereas the greenhouse-gas emissions from yard waste composting are similar to those from landfills. The Compost Council argues that keeping food and grass clippings out of landfills significantly reduces methane emissions, and that the CO2 produced, being from plants, does not count as anthropogenic gas.

Home compost techniques and systems vary so widely that we can only tentatively generalize: They are insignificant producers of greenhouse gases. An aerobic compost pile has oxygen available to the decomposing organisms — either because the composter (you) turns the pile regularly, or because of worms — and hence avoids the methane production that would occur in an anaerobic landfill setting. Any methane produced in an anaerobic pile (one that just sits there with no help from you and that likely smells of ammonia) will develop in the stinky core of the pile and may vanish as it travels through the more aerobic outer layers, reacts with oxygen, and transforms into some other compound.

A pile of brown leaves has wonderful purposes in the garden, either used fresh in the autumn or stored for a bit and used in its leaf mold state. Pile leaves loosely to let air circulate, and your Climate Conscience should be trouble-free. As to your neighbor, if his leaves are clean, take them, too, to supply your garden with even more excellent mulch. Or just leave him to do as he wishes, but feel free to point out the beauty and low expense of your own yard.