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Urban ‘green’ spaces may contribute to global warming

Dispelling the notion that urban “green” spaces help counteract greenhouse gas emissions, new research has found — in Southern California at least — that mowing and other lawn maintenance emit much larger amounts of greenhouse gases than the well-tended grass sequesters.

Turfgrass lawns remove carbon dioxide from the atmosphere through photosynthesis and store it as organic carbon in soil, making them important “carbon sinks.” However, greenhouse gas emissions from fertilizer production, mowing, leaf blowing and other lawn management practices are four times greater than the amount of carbon stored by ornamental grass in parks, a new study shows. These emissions include nitrous oxide released from soil after fertilization. Nitrous oxide is a greenhouse gas that’s 300 times more powerful than carbon dioxide, the Earth’s most problematic climate warmer.

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“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,” says Amy Townsend-Small, Earth system science postdoctoral researcher at University of California, Irvine. Townsend-Small is the lead author of the study, which has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union (AGU).

The research results are important to greenhouse gas legislation being negotiated, Townsend-Small says. “We need this kind of carbon accounting to help reduce global warming,” the lead author says. “The current trend is to count the carbon sinks and forget about the greenhouse gas emissions, but it clearly isn’t enough.”

via AGU