Composting Contributes to Climate Change?

Composting is good for the earth, right? It takes waste and transforms it into not just something usable, but something that helps us grow food. It has become so popular, that many cities around the world are starting large-scale composting projects. But, Sustainablog reports that even the most conscientious large-scale composting operations emit methane, a greenhouse gas.

From Sustainablog:

There are actually very few published scientific studies about greenhouse gas emissions from composts, but the two that I have been able to find show that around 2-3% of the original carbon in the manure or green waste is emitted as methane (21X carbon dioxide in GHG potential) and there is also a little nitrous oxide as well (310X carbon dioxide in GHG potential).  That doesn’t sound at all bad until you do some math with the values in these publications.

If you think of it in terms of delivering a hundred pounds of nitrogen/acre (as you would for something like an organic vegetable crop) you would need to start with 8600 pounds (on a dry weight basis) of cow manure (because there is a loss of mass and because the compost is only 1.7% nitrogen).  The greenhouse gas emissions are the equivalent of 0.74 lbs CO2 per dry lb of manure.  That means that the “carbon footprint” of the 100 lbs of N in compost fertilizer is 6,403 lbs CO2.  That is 14.6 times as much as for synthetic urea fertilizer! It is the equivalent of burning 331 gallons of gasoline! (if you are interested you can see a more detailed explanation).

Sustainablog’s math was confirmed by USDA scientists.

So, does that mean that those of us with backyard compost piles should stop recycling our food and garden scraps into fertilizer? Definitely not. And it doesn’t mean that large-scale composting operations should be halted either. Sustainablog will have future posts on possible solutions, so stay tuned.

But a commenter named Ken at the Sustainablog website made a great point: “Composting converts what might otherwise be tossed into a landfill (or burned) into useful soil organic matter. Carbon will be released no matter what is done – the proper question is which choice produces the most appropriate benefit along with those costs.”

Link [Sustainablog]
Photo Credit: Flickr user normanack

Related Posts:

Robot Nixes Stench of Indoor Composting
Researchers Collecting Cow Flatulence in Plastic Tanks to Study Global Warming
Cow Burps Responsible for More Greenhouse Gases than Cars
Arctic Sea ‘Foaming with Methane’ as Permafrost Melts
Oozing Methane Has Scientists Worried About Climate Catastrophe