Leaf blowers, lawn mowers and fertilizer: How lawns contribute to climate change
Americans are in love with — or, some might say, addicted to — their lawns. The neatly manicured, bright green plots of grass are ubiquitous in most suburbs, where a majority of Americans live. At least 40 million acres in the United States, an area larger than the state of Georgia, are covered by turf grass, the standard lawn plant.
But what if growing and grooming that grass is contributing to the biggest environmental crises on the planet, including water pollution and climate change?
That’s the view of a number of scientists who are increasingly vocal about the drawbacks of lawns and the need to switch to alternatives — or, at a minimum, more sustainable means of managing one’s lawn.
“There are four things every piece of land needs to be doing if we’re going to reach ecological sustainability: sequester carbon, support pollinators, support a food web. And the other is to manage the watershed. A lawn is the worst choice in all of those four ecological goals,” Douglas Tallamy, a professor of agriculture and natural resources at the University of Delaware, told Yahoo News.
For climate change, the single biggest problem is not what a lawn does, but what it doesn’t do. Every plant stores carbon dioxide — the most widespread heat-trapping gas that is causing global warming. The more carbon that’s stored, the better it is for the environment. But not all plants store the same amount of carbon. Broadly speaking, the amount of carbon sequestered correlates to the size of a plant and its root system. That’s why logging old-growth trees, which tend to be taller than younger trees, is particularly bad for climate change.
Compared to other plants that could grow in a yard, like bushes and trees, lawn grass has a very shallow root system. Much less of it grows above ground, especially if you cut your grass every week to keep it neat and short. “In terms of carbon sequestration, lawns fail,” said Tallamy, the author of “Nature's Best Hope: A New Approach to Conservation That Starts in Your Yard.”
Then there’s the lawn maintenance and machinery that many Americans use to cut and clean their lawns: gas-powered lawn mowers and leaf blowers. According to the Environmental Protection Agency, gas-powered lawn mowers use 800 million gallons of gasoline — and spill an additional 17 million additional gallons of oil — every year. The two-stroke engines used by lawn mowers and leaf blowers are especially dirty because they do not combust about 30% of the fuel they use, which releases volatile organic compounds.
A 2014 study found an idling scooter with a two-stroke engine releases 124 times as much volatile organic compounds as an idling car or truck. The EPA states that using a typical gas-powered lawn mower produces as much volatile organic compounds and nitrogen oxide — a powerful greenhouse gas — as driving 11 average new cars over the same timeframe. In total, according to the agency, lawn mowers account for 5% of American (non-climate) air pollution. On top of that, many lawns are cut by a gardener who visits regularly, burning gasoline on the way there and back.
“Lawns are fossil fuel-dependent, period,” Douglas Kent, a landscape contractor who teaches at Cal Poly Pomona, told Yahoo News. “They don’t have to be, it’s just how we maintain them — the mowers, the blowers, the edgers.”
Then there are the emissions associated with making fertilizer. The most important ingredient in fertilizer is typically ammonia, which contains nitrogen that helps plants grow. Ammonia is made at high pressure and at high temperatures. So it requires a lot of energy, which is usually supplied by fossil fuels like coal and natural gas. Ammonia manufacturing is responsible for more than 1% of global greenhouse gas emissions.
“[Lawns] are huge nitrogen consumers, and nitrogen is the most energy-dense nutrient that we manufacture,” Kent said.
“When you add all that energy we’re dumping in lawns and compare it against the amount of biomass that’s being stored in the soil and the tissue, you come up with 1 acre of lawn [that] contributes approximately 3,112 pounds of carbon dioxide per year, which has the energy equivalent of 156 gallons of gasoline,” Kent added. (He made that calculation, drawing on previous research for the data inputs, for his book, “A New Era of Gardening: A Book on Gardening for Oxygen and a Healthier Atmosphere.”)
Many of the same attributes that make most well-manicured American lawns a net contributor to climate change also cause them to fail Tallamy’s other sustainability tests. Fertilizer, for example, typically comes mixed with herbicide to kill off weeds — the two-in-one products are referred to as “weed and feed.”
But a person’s weed is an insect’s food. The weeds that pollinators depend on, such as clovers and dandelions, are being systematically eliminated from lawns every day. And pollination is the very basis of biodiversity.
“Most vertebrates don't eat plants directly: They eat things that eat the plants, mostly insects,” Tallamy observed.
Likewise, short, regularly cut grass does not absorb much water — an increasingly important task as climate change leads to more flooding from heavier storms — and that runoff can funnel fertilizer and herbicide into lakes, rivers and oceans, potentially poisoning fish and harming swimmers.
“Lawns are destroying our watersheds, because, first of all, they don’t hold the water that other plants are holding,” Tallamy said. “It’s almost like paving the ground during a hot, dry summer.”
Grass is the most prevalent irrigated crop in the U.S., and lawns use 3 trillion gallons of water per year. Due to the warmer temperatures and more severe droughts associated with climate change, water scarcity has become a crisis in much of the West, forcing local governments to limit the amount of water residents can use outdoors, although many homeowners are reportedly ignoring the rules.
To be sure, lawns are not the only detrimental yard features. A concrete patio, which comes with its own carbon emissions from concrete production, has no ecological benefits at all.
So ripping out a lawn and paving it over would not be helpful. But what should you replace it with? Most experts suggest simply reducing the amount of space dedicated to grass and swapping in some bigger plants that will absorb more carbon and water. A tree that provides shade also reduces the amount of water that evaporates from the remaining lawn, meaning that it should require less water.
Ideally, some scientists say, only people living in regions wet enough to grow grass without additional watering would have lawns, and residents of drier regions would plant less thirsty native species, like cactus in the desert.
There are also lower-impact ways of caring for a lawn. Using only manual tools, like a push mower, or electric ones, will remove the emissions from two-stroke engines. According to the Electric Power Research Institute, replacing half of gas mowers in the United States with electric mowers would save as much emissions as taking 2 million cars off the road. Taking a more natural approach to lawn management — cutting it less often, skipping the weed killer and letting the clovers and dandelions grow — would also minimize the impact.
Some state and local governments are beginning to take action on the worst environmental drawbacks of lawns. Responding to complaints about the noise of gas-powered mowers and leaf blowers as much as the emissions, California Gov. Gavin Newsom signed a bill last October that will phase them out in the state.
“Right now, we use [lawn] as a default landscape: We put a few plants in our yard and everything else becomes lawn,” Tallamy said. “I want to turn that on its head. I want to have a lot of plants, and what’s left over becomes lawn.”