Green is good, right?
Not necessarily when it comes to lawns, according to a new study by UC Irvine researchers.
For the first time, scientists compared the amount of greenhouse gases absorbed by ornamental turf grass to the amount emitted in the irrigation, fertilizing and mowing of the same plots. It turns out keeping a lawn is not good for Mother Earth.
In four parks near Irvine, researchers calculated that emissions were similar to or greater than the amount of carbon dioxide removed from the air through photosynthesis -- a finding relevant to policymakers seeking to control the gases that trap heat in the atmosphere and contribute to climate change.
“Green spaces may be good to have,” said geochemist Amy Townsend-Small, the lead researcher in the paper published in the journal Geophysical Research Letters. “But they shouldn’t be automatically counted as sequestering carbon.”
The paper is particularly timely, she added, because governments are calculating their carbon footprints and discussing whether parkland could offset other sources of emissions, such as refineries, power plants and automobiles.
Turf grass, covering an estimated 1.9% of the United States, is the most commonly irrigated crop and increasingly in demand in urban areas.
Townsend-Small and colleague Claudia Czimczik measured the carbon content of the parks’ soil and compared that with emissions from producing fertilizer, mowing with gasoline-powered equipment and pumping water to irrigate the plots. The water was recycled; but if it were fresh water transported from distant rivers, as is much of Southern California’s water, emissions would be higher, Townsend-Small said.
They also factored in the nitrous oxide released from soil after fertilization. Nitrous oxide is a greenhouse gas 300 times more powerful than carbon dioxide, which is released by fossil fuel combustion.
California has no regulations to control turf grass, but the study “shows the importance of full life-cycle analysis for greenhouse gases,” said Mary Nichols, head of the California Air Resources Board, which is charged with reducing the state’s carbon footprint. Research is underway, she said, to develop varieties of grass that need less mowing and use less water.
Southern Californians, Townsend-Small said, could reduce the carbon footprint of their lawns by using rakes rather than leaf-blowers and hand mowers rather than gasoline-powered equipment.
“About 40% of the drinking water we import at great financial and environmental expense is used for ,” said Paula Daniels, a Los Angeles Department of Public Works commissioner. “This study hopefully will motivate more of us to make changes in our landscapes.”