Human Journey

The Grass Isn’t Always Greener — At Least for Your Lawn

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Turns out the grass isn’t always greener, at least when it comes to lawns and their contribution to global warming.

That’s because keeping those green spaces glossy with fertilizer and other maintenance techniques actually offsets lawns’ carbon-trapping benefits, according to a new study in Geophysical Research Letters.

“Turfgrass” lawns, which make up nearly 2 percent of land in the continental U.S., act as carbon sinks, storing the powerful greenhouse gas in soil.

But if you consider what it takes to upkeep a lawn–that is, production of fertilizer, mowing, leaf blowing, and other practices, their collective greenhouse gas emissions are four times greater than the amount of carbon that lawns can absorb.

For instance, fertilizer releases nitrous oxide–commonly known as “laughing gas”–a greenhouse gas that’s 300 times more potent than carbon dioxide.

“Lawns look great–they’re nice and green and healthy, and they’re photosynthesizing a lot of organic carbon. But the carbon-storing benefits of lawns are counteracted by fuel consumption,” study leader Amy Townsend-Small of the University of California, Irvine, said in a statement.

Nitrous Oxide Emissions No Laughing Matter

Townsend-Small and colleague Claudia Czimczik focused on four parks in Irvine, each of which had two types of turf: athletic, for soccer and baseball, and ornamental, which includes picnic areas.

Over a year, the team took soil samples in the parks to measure how much carbon was stored. Researchers also measured how much nitrous oxide was being released by sampling air above the surface, and then estimated carbon dioxide emissions based on lawn-upkeep activities.

Not only did the irrigation, fertilizer, and other activities dwarf the lawns’ ability to store carbon, the nitrous oxide emissions were similar to those of agricultural farms, which are among the largest emitters of the gas in the world.

Although the study was limited to city parks, “there’s still the potential to reduce the carbon footprint of all lawns by reducing fossil fuel consumption,” Townsend-Small told Green Guide in an email.

For instance, she recommends using a rake and a push mower instead of leaf-blowing or power mowers, and limiting irrigation and use of synthetic fertilizers and pesticides.

–Christine Dell’Amore

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Photograph by Philip Gould, NGS

More from National Geographic’s Green Guide:

Easy Organic Lawn Care

Fertilizer Buying Guide

Green Guide Home & Garden Hub

Christine Dell'Amore, environment writer/editor for National Geographic News, has reported from six continents, including Antarctica. She has also written for Smithsonian magazine and the Washington Post. Christine holds a masters degree in journalism with a specialty in environmental reporting from the University of Colorado at Boulder. Her book, South Pole, was published in 2012.

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