Mowing Down Greenhouse Gases

Global warming finally captured mainstream news headlines last week when reality star President Trump declared he would pull the United States from the Paris Climate Agreement. While withdrawing from the agreement will have negative environmental and economic ramifications that won't manifest themselves for years, maybe even decades, I won't pretend to be surprised by this turn events, just like I wasn't surprised by the Dakota Access Pipeline getting rammed through. I've long believed that any meaningful action to curb global warming would come from the private sector and local efforts.

To that end, it's been encouraging to see cities like Pittsburgh pledge to go 100% renewable, and cities like Oakland block the construction of coal terminals in their ports, largely thanks to pressure from local groups. Similarly, municipalities, academic institutions, and churches have been divesting from the fossil fuel industry. All of these efforts began well before Trump became president and can continue despite his efforts to gut environmental regulations.

My electric, mulching mower has a
lot of miles on it...for good reason

As individuals, we have little control of federal legislation, but we can take individual efforts and band together to put pressure on businesses and local governments.

One avenue that I feel has been overlooked is a simple one: mulching our lawns instead of bagging out the grass clippings. I know, I know, it sounds sort of stupid, but hear me out.



Turf grass covers between 16 and 20 Mha (62,000 - 77,000 square miles) of grass in the US(1). Most lawn clippings are bagged when mowed and sent to the landfill where the clippings rot and produce methane, a strong greenhouse gas. Even so, a modeling study performed by Christina Milesi at the University of Montana calculated that US lawns sequester 5.9 teragrams of carbon per year. If everyone simply left lawn clippings on their lawns rather than bagging them out mowing, that figure would go up to 16.7 teragrams of carbon per year (~37 billion pounds) according to the study (2). That’s a 270% increase! The net difference would be even larger because that green waste would no longer be creating methane in landfills. In addition, the clippings would fertilize the lawns, decreasing the amount of fertilizer needed (most figures suggest a 25% reduction, but Milesi’s study projects a 50% reduction).

Newer research as part of the Marin Carbon Project has shown soil carbon sequestering actually works. An experiment conducted by the Project showed that spreading only half an inch of composted green waste on rangeland resulted in sequestering 1 ton of carbon per hectare over a three year period. In addition, application of the compost led to a 50% increase of plant growth and improved water retention (3).

What's all this mean? On an individual level, ditch the lawnmower bag and stick in your mower's mulching plug if it has one, or just let the clippings shoot out the side onto the lawn to help fertilize your grass and turn it into a carbon sink. (And go with an electric mower, if you haven't already!) If you live in a rural area, go large-scale with the same idea. Contact your local landfill to see if they sell or giveaway the compost they create, and put it to good use in your pasture land.

On a community scale, we could push for local legislation that forces landscaping companies (who are responsible for most lawn care in affluent neighborhoods) and city employees (who are responsible for lawn care of our parks and other public lands) to employ mulching techniques. This route would probably require a bit more research than what I've put in--something official from an nonprofit organization that could be compiled in an informational flier that could then be passed on to city council members, county supervisors, and whatnot.

Mulching lawns certainly isn't a fix-all when it comes to global warming, but it could sequester a lot of carbon and help mitigate some of our carbon emissions until such time the US gets serious about cutting said emissions. It's something, at least, and it's in our power to control, so I for one and am all about it.

-Garrett Calcaterra

If you have ideas for improvements, or other ideas of your own for action we can take on an individual or community level, please share them in the comments. Anything and everything helps.

Sources

1. http://www.walterreeves.com/uploads/pdf/lawncarbonsequestration.pdf
2. http://earthobservatory.nasa.gov/Features/Lawn/lawn3.php
3. http://www.marincarbonproject.org/science/land-management-carbon-sequestration

Author's Note

I first wrote about this idea last year in the discussion forums for Project Hieroglyph (now archived, it seems). My post went largely unnoticed, perhaps because of the boring nature of the idea compared to building space elevators and self-replicating robots on the moon. Anyhow, I'd given up on writing about the idea, but then my friend, author Juniper Nichols, posted a related article from UC Davis a few weeks ago. That inspired me to re-post my proposal for grass clippings here on my blog (where it will likely go largely unnoticed, too, but so it goes).