The Most Effective Ways to Shrink Your Carbon Footprint

A study published in July 2017 by researchers from Lund University (Sweden) and the University of British Columbia (UBC) claims to have identified the most effective actions individuals can take to reduce their greenhouse gas emissions. The top four, according to the study, are having one fewer child, living car-free, avoiding airplane travel, and eating a plant-based diet. The authors warn that school textbooks and government agencies send the wrong message by failing to emphasize these opportunities, focusing instead on promoting much lower-impact actions such as changing lightbulbs or recycling.

There’s just one problem: two of the top four actions may not actually be effective at all, unless many individuals take them collectively.

Let’s look at airplane travel first. When you fly somewhere, you are arguably responsible for a share of the airplane’s greenhouse gas emissions (the study cites a figure of 1.6 metric tons of CO2 equivalent per passenger for a transatlantic flight). Unlike public transit, where buses and trains run on a schedule regardless of whether any passengers are on board, airlines will cancel a flight if not enough people book tickets. Therefore, the argument goes, each passenger assumes responsibility for a share of the plane’s emissions: if none of them chose to fly, the flight would be cancelled.

Those are somewhat oversimplified assumptions, but they’re widely accepted. The problem comes when you look at it in the other direction: if I choose to not fly, am I actually avoiding any emissions? In most cases the answer is no.

If I choose not to take Flight 123 from New York to London, Flight 123 will likely still fly and those emissions will still occur. The only cases in which choosing not to fly will have an impact are when I happen to be the marginal passenger on an under-booked flight who tips the balance between the plane flying or not flying. In these days of alliances among airlines, in which one airplane is filled with passengers who’ve booked seats via several carriers, the chances of my being that marginal passenger are slim. In fact, I could choose to not fly for the rest of my life without actually preventing a single plane from taking off.

This illustrates a curious problem in personal carbon accounting: I am responsible for a share of the emissions resulting from actions I take, but — in certain cases — if I change my behaviour I may not actually reduce those emissions at all.

Switching to a plant-based diet presents a similar problem. Google “how many vegetarians does it take to save a cow?” and you’ll find endless debates about the actual impact a person can have by avoiding meat. Sure, there’s a supply-and-demand relationship, but it’s complex. If I avoid eating meat for the rest of my life, will it have a measurable effect on meat production? Possibly, but is that impact as large as the 0.8 metric tons of CO2 equivalent per year estimated in the study? I’m skeptical, and I certainly don’t think this qualifies as a “highly effective” individual action to reduce emissions. “Highly effective” implies that you’re making a difference (i.e., your decisions are having an impact in the real world), and I don’t think that can be demonstrated in this case. We need a more rigorous evaluation of how individuals’ demand for meat affects supply, and the extent to which changes in production can be traced to individual actions (Bailey Norwood’s analysis in Compassion by the Pound is a good place to start learning about this).

It’s important to look at these actions from the atmosphere’s perspective, not from a carbon accounting perspective. People take action to reduce their carbon footprint because they want to make a difference. From a carbon accounting perspective it’s easy to show that avoiding a flight or avoiding a hamburger has reduced your footprint. But if you haven’t actually prevented an airplane from flying or livestock from being raised and slaughtered, are you making a difference? If you refuse a printed receipt offered by a cashier because you’re following a zero-waste lifestyle, have you actually reduced waste or simply reallocated it to someone else (the store)? If you refuse to fly, have you caused a flight to be cancelled or are you simply reallocating the flight’s emissions among the passengers who do fly (meaning each of them is responsible for a greater share of the plane’s emissions)?

Me vs. We

There are actions people can take that may only have an impact if they are taken collectively. If I alone choose not to fly it may have no effect on greenhouse gas emissions, but if 50,000 or even 5,000 people choose not to fly it probably will. Similarly, a large number of people who choose to become vegetarians (or even just commit to meatless Mondays) can collectively have an impact on meat production. But this is not so different from the supposedly “low impact” actions identified in the Lund-UBC study like changing light bulbs. Switching your household’s light bulbs from incandescents to LEDs will have about as much impact as the proverbial fart in a hurricane. But if 200,000 households in a region do it, the electric utility might be able to avoid firing up a peaking power plant. That makes a difference.

The question “what are the most effective actions I can take to reduce my carbon footprint?” should be examined from both angles: 1) what are the biggest bang-for-the-buck actions I can take to reduce my own personal impact, and 2) how can I contribute to actions that have a big impact collectively?

Every molecule of CO2 released to the atmosphere stays there on average for 100 years, trapping heat. That means everything you do to reduce emissions will make a difference, however small. But first you have to be sure your actions will actually reduce emissions.

Low-Hanging Fruit

I agree with the Lund-UBC study’s finding that living car-free and having one less child are likely to be high-impact actions. If you don’t drive, you avoid burning gasoline. Even if you take public transit instead of driving, you’re not personally responsible for a share of the bus’s or train’s emissions, because public transit runs regardless of how many passengers are on board.

Having one less child, especially one less North American or European child, makes an obvious difference to emissions as well, unless you, as a carbon-conscious parent, raise your child to be the next Al Gore (who has certainly convinced many people to reduce their emissions and thus probably has avoided more emissions than he has caused, despite claims that he doesn’t walk his talk).

The problem is that living car-free and having one less child can be hard decisions. I’ve lived car-free for three years now and love it, but I live in a big city with ample public transit and bike paths. I wouldn’t have attempted it during the 20 years I lived in rural New England. As for having one less child, that’s a decision that pits environmental values against personal dreams and desires. For some people it’s no sacrifice; for others it’s a heartbreak.

This, in fact, is why textbooks and government agencies focus on the supposedly low-impact actions like changing lightbulbs and recycling. They’re easy, they’re the low-hanging fruit. They won’t affect your personal carbon footprint very much, but precisely because they’re easy they’re more palatable for a large number of people to adopt. And a large number of people taking small actions can lead to big changes.

My Recommendations

I’ve spent a lot of time thinking about how to reduce my own personal carbon footprint, and have spent 17 years working on carbon calculators (including the U.S. EPA’s Household Carbon Footprint Calculator and EPA’s Greenhouse Gas Equivalencies Calculator). Based on that experience, here’s my perspective:

If you’re looking for actions you can take that have a high-confidence, high-impact ability to reduce your contribution to climate change, I’d focus first on ground transportation. Anything you do to avoid burning gasoline, whether it’s avoiding driving or driving a more fuel-efficient vehicle, is going to have an impact. The impact of electric cars varies according to the power mix (the different sources used to generate electricity in your area); if you live in the United States you can use the U.S. EPA’s Power Profiler tool to learn about your region’s power mix. Changing transportation choices and behaviours is hard for many people: it can be disruptive and expensive. But it’s also the area where most individuals can make a the biggest difference.

I’d also focus on reducing food waste, through better management of your household’s groceries, by composting, or ideally both. Rotting food in landfills can generate methane, which is more than 20 times more effective at trapping heat (on a molecule per molecule basis) than CO2. If you do compost at home, be sure to turn your compost regularly so it doesn’t produce methane itself.

If you heat your home with fossil fuels (e.g., natural gas, heating oil, or propane), you can directly reduce emissions by improving home insulation or upgrading to a more efficient boiler or furnace.

For the actions that mainly make a difference collectively, if many people do them, follow all the usual advice: use LED lightbulbs, always buy Energy Star appliances and other equipment, unplug electronics when not in use to avoid trickle charges, recycle and source-reduce (avoid buying things, buy used or refurbished, reduce or avoid packaging), eat less meat, fly less. You can also purchase offsets to cancel your emissions, although your impact will be more certain if you reduce your emissions as much as feasible first and offset the remainder.

The Lund-UBC study is an excellent first step toward identifying the most effective actions individuals can take to reduce their emissions. But it raises many questions about which actions actually result in real-world changes.