Urban parks and suburban lawns are bad for the climate. This week, that topic has been the subject of a media blitz triggered by a new study at UC Irvine titled “Carbon sequestration and greenhouse gas emissions in urban turf”.
Truthfully, I’m disappointed by the tone of mild surprise adopted in every article I’ve read. The fact that your classic American lawn is bad for the environment is very old news. Watered year-round, kept emerald green by chemical fertilizers and dandelion-free by herbicides; trimmed and tidied with gas-guzzling mowers and leaf blowers – this is not an environmentally sustainable space! For decades, native plant gardens, rock gardens, and urban natural areas have been promoted by green thinkers.
The UC Irvine study helpfully quantifies the damage (at least as it occurs in Southern California), but the media it has received does its audience a disservice. While an academic discussion has been going on about the possibility of sequestering carbon in turfgrass, that conversation hasn’t filtered into the public consciousness. By claiming that the study “dispels” the notion that “urban "green" spaces help counteract greenhouse gas emissions,” that very notion is in fact created by bulldozing over a nuanced subject.
For example, “urban green spaces” can be forests, gardens, green rooftops, managed natural areas, lawns, and golf courses. Some of these have a positive environmental impact; others have a negative one. Lumping them together is a mistake.
The study itself, which has not yet been released to the public but is in press in the journal Geophysical Research Letters, appears to capture the nuance of the subject, specifically addressing previous studies that have documented lawns storing carbon, but haven’t looked at the emissions associated with tending them. The study shows that nitrous oxide emissions from lawns are comparable to those found in agricultural farms, which (according to the press release) are among the largest emitters of nitrous oxide globally. And nitrous oxide is a greenhouse gas that's 300 times more powerful than carbon dioxide.
In ornamental lawns, nitrous oxide emissions from fertilization offset just 10 percent to 30 percent of carbon sequestration. But fossil fuel consumption for management, the researchers calculate, releases about four times more carbon dioxide than the plots can take up. Athletic fields fare even worse, because — due to soil disruption by tilling and resodding — they don't trap nearly as much carbon as ornamental grass but require the same emissions-producing care.
“It's impossible for these lawns to be net greenhouse gas sinks because too much fuel is used to maintain them,” study author Amy Townsend-Small concludes. Which is indeed useful information – but perhaps the media should be asking who is making the counterargument that inspired her research? And why?
