Urban 'green' spaces may contribute to global warming, study finds

Urban 'green' spaces may contribute to global warming, study finds
Amy Townsend-Small, Earth system science postdoctoral researcher, found that management of urban "green" spaces can emit more greenhouse gases than the plots take in and store. Photo by Steve Zylius / University Communications

Dispelling the notion that urban "green" spaces help counteract greenhouse gas emissions, new research has found - in Southern California at least - that total emissions might be lower if lawns did not exist.

Turfgrass lawns help 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 similar to or greater than the amount of carbon stored by ornamental grass in parks, a UC Irvine 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.

"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 can be counteracted by greenhouse gas emissions," said Amy Townsend-Small, Earth system science postdoctoral researcher and lead author of the study, forthcoming in the journal Geophysical Research Letters.

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

Turfgrass is increasingly widespread in urban areas and covers 1.9 percent of land in the continental U.S., making it the most common irrigated crop.

In the study, Townsend-Small and colleague Claudia Czimczik analyzed grass in four parks near Irvine, Calif. Each park contained two types of turf: ornamental lawns (picnic areas) that are largely undisturbed, and athletic fields (soccer and baseball) that are trampled and replanted and aerated frequently.

The researchers evaluated soil samples over time to ascertain carbon storage, or sequestration, and they determined nitrous oxide emissions by sampling air above the turf. Then they calculated carbon dioxide emissions resulting from fuel consumption, irrigation and fertilizer production using information about lawn upkeep from park officials and contractors.

The study showed that nitrous oxide emissions from lawns were comparable to those found in agricultural farms, which are among the largest emitters of nitrous oxide globally.

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 calculated, released almost as much or more carbon dioxide than the plots could take up, depending on management intensity. Athletic fields fared even worse, because - due to soil disruption by tilling and resodding - they didn't trap nearly as much carbon as ornamental grass but required the same emissions-producing care.

"It's unlikely for these lawns to act as net greenhouse gas sinks because too much energy is used to maintain them," Townsend-Small concluded.

Previous studies have documented lawns storing carbon, but this research was the first to compare carbon sequestration to nitrous oxide and carbon dioxide emissions from lawn grooming practices.

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Provided by University of California - Irvine
Citation: Urban 'green' spaces may contribute to global warming, study finds (2010, January 19) retrieved 20 June 2019 from https://phys.org/news/2010-01-urban-green-spaces-contribute-global.html
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Jan 20, 2010
Another Physorg headline I just read:
Earth hasn't warmed as much as predicted because we might have greatly overestimated the effects of greenhouse gases and earth sensitivity to CO2.

This article:
Your lawn might be killing the planet because it's releasing CO2.

Does anyone else have a problem with making predictions and assumptions based on other models with more (apparently wrong) assumptions, then based on data that is also incomplete. It's called margin of error. And in the case of global warming, it's so huge that I can't take any article like this seriously. Physorg certainly seems to like enjoy them, though

Jan 20, 2010
...in an ecologically unsustainable way...

Define "ecologically unsustainable way".

What alternative do you suggest? I've personally experienced "consumer savvy" lifestyle under communist regime. Did you? There is nothing enjoyable there, believe me.

Jan 20, 2010
So just use compost and human-powered gardening tools. Save the environment and lose weight at the same time.

Jan 20, 2010
I wouldn't call a lawn an urban green space. Green spaces should have shrubs and trees and maybe some lawn for people to rest/play on.

Jan 20, 2010
I believe the problem (especially between the two stories) lies in the confusing opinions. Half of the stories spell doom, and the other half say there is nothing to worry about.

Myself, I tend to believe the one's that spell doom. I can't believe all the chemicals we spew forth into the air isn't having ANY effect.

Even if the effect is a small one, if we take to heart the worst case, and try to resolve the problem, we will be better off in the long run.

Jan 20, 2010
What if we used those old un-powered mowers?

Jan 20, 2010
As somebody commented on wattsupwiththat, the story makes a perfect SNL news punchline:

- Global warming scientists found that lawns contribute to greenhouse gasses.
- The lunatics are on the grass!

Jan 24, 2010
What if we used those old un-powered mowers?

While we're at it, lets do away with all technology, and do everything by manual labor like 500 years ago...

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