Preface: I was an early adopter of electric lawn mowing. Early, in this case, being somewhere around 1995, well before battery-powered electric mowers existed. But after a couple of burnt-out mowers and many trashed extension cords, I gave up and bought an efficient gas walk-behind mower.
That was circa 2015, and I have not looked back. Until now. This is the first of a series of posts looking at gas versus electric lawn mowing.
Part 1: The conundrum
I keep reading ever-more-outlandish statements about just how much pollution gas lawn mowers generate. Depending on which source you read, you will come across this generic format:
- One hour of mowing your lawn using some gas-powered lawn device
- produces as much something-something-something
- as 200 or 300 or 350 miles of driving something.
Weirdly enough, it’s always one hour. Everything else varies from source to source. In addition, I am not the only person to have noticed that these car-versus-mower statements are all over the map. This has gotten to the point where the EPA apparently doesn’t support statements like this any more (reference).
I’m sure there’s some truth in there, somewhere, but that has the look of a standard advocacy statement. Typically, if you take one of those apart, you’ll find that somebody has purposefully created a worst-possible-case-vs-best-possible-case contrast. Statements like that are crafted to convince rather than to inform. And that’s done with forethought, in pursuit of some presumed policy or economic goal.
Worse, as variants of that get tossed around, further and further from the actual research, they start to take on urban legend aspects.
Let’s play “spot the loony”. Consider this statement, from an otherwise reputable source, Family Handyman magazine:
One hour of running a gas mower emits as much carbon dioxide as driving a car 300 miles, ...
That’s obviously a mistake. Carbon dioxide (C02) emissions are directly proportional to the amount of gasoline burned. Each gallon of gas generates about 20 pounds of C02 (Source: EPA). The average new (2021) U.S. passenger vehicle, including electric and plug-in cars, gets less than 25 MPG or equivalent (Source: EPA). Taken literally, the statement above says that a lawn mower burns (300/25 =) 12 gallons of gas per hour?
Must be one hell of a lawn mower. Big agricultural combines (as above) can easily have that level of fuel consumption. But not your typical 21-inch 3.5 HP Briggs and Stratton lawn mower.
My wife confidently informs me that we burn two gallons of gasoline per year, cutting our grass. She’s confident because a) she mows the lawn, and b) she hates putting the gas can in her car. So she’s sure she does that once per season. This, on a half-acre suburban plot, less the footprint of house, driveway, and landscaping.
By contrast, for cars, in the U.S., we burn an average of about 650 gallons of gasoline per licensed driver per year (Source). For me and my wife, if we were average, we’d be burning 1300 gallons of gasoline per year, in our car. (We aren’t — we drive a Prius Prime and arguably use about 40 gallons of gas per year in that.)
Plus two more gallons, for the lawn mower.
So there’s the conundrum. Where does this gas-lawn-mower-as-environmental-horror-story come from, given how little fuel the typical suburbanite consumes for lawn mowing, compared to driving?
For sure, the carbon footprint of our gas lawn mower is rounding error in the context of total household fossil fuel use. Not because small gas engines are any great shakes. Simply because the fuel used to mow the lawn is negligible.
For perspective, using Virginia’s power generation mix (0.65 lbs C02 per KWH), two gallons of gasoline generates as much C02 as 60 kilowatt-hours, or roughly 160 watt-hours per day. Based on these typical wattages, the gas lawn mower has the same carbon footprint as the following daily use of these home appliances:
In short, for my primary environmental concern — global warming — mowing the lawn just doesn’t matter. Or, it matters less than many other common activities of daily living, such as washing dishes or watching TV.
But I still would like to know the full story here, Given the small amount of gasoline consumed, how closely does whatever-it-is that is the underlying research actually apply to my situation? Should I consider early retirement for my gas lawn mower, in favor of battery-powered? Should I plan on buying a battery-powered mower if and when my current one dies?
I already know some of the answers.
Briefly: First, the horror story is about smog (not carbon footprint). Second, it focuses on major small-engine consumers of gasoline. The total environmental impact appears to have been estimated based on consumption of 3 billion gallons of gasoline annually, for lawn and garden equipment. With lawns surrounding roughly 100 million U.S. households, that works out to about 30 gallons of gas, per lawn, per year. Or about 15 times the rate at which my mower uses gas.
The upshot is that I’m not deeply concerned about this. But I would like to know more. The rest of the posts in this series will dig a little deeper into this, including (if possible) finding the original EPA research that has spawned this class of gas-lawn-mower-bad advocacy statements.
More to come. It’s a nice day. I’m going to go work in the yard now.
