By Katie Watkins

WASHINGTON — For Americans interested in reducing their carbon footprint, a new Canadian-Swedish study has a bold proposition: Consider having fewer children.

Researchers from Canada’s University of British Columbia and Sweden’s Lund University analyzed 39 peer-reviewed studies, government reports and carbon calculators from 10 different countries, including the United States, to compare how various eco-friendly measures, such as recycling and driving an electric car, stack up.

After crunching the data, they listed four major lifestyle changes people can make to reduce emissions in developing countries: have fewer children, stop driving, avoid air travel and eat a plant-based diet.

“These actions have much greater potential to reduce emissions than commonly promoted strategies like comprehensive recycling (four times less effective than a plant-based diet) or changing household lightbulbs (eight times less),” Seth Wynes and Kimberly Nicholas write in the study.

Wynes acknowledges, however, that he and his colleagues are not suggesting that everyone should or even could adopt such major and very personal changes. Rather, he said the information should be readily available for adolescents as they make lifestyle choices, and might be more likely to adopt these types of behaviors.

“There’s a difference between a 50-year-old suburbanite with an established lifestyle being asked to consider some of these changes, compared to someone who is just starting out on their adult life, and can make decisions like I’m going to live closer to where I work so that I don’t need a car in the first place,” Wynes said in an interview.

A former high school science teacher in Canada, Wynes said students often asked him what steps they could take to reduce their personal impact on climate change.

“At the time that I had those conversations I knew sort of a long list of actions that were positive for the environment, but I had no idea which ones were actually more important,” Wynes said.

So, as a Ph.D. student at the University of British Columbia, he worked with Nicholas, an associate professor of sustainability science at Lund University, to analyze the data. They also found that Canadian textbooks and government documents in Australia, the United States, Canada and the European Union rarely mentioned the four actions with the biggest impact, highlighting smaller steps instead.

“The thing that surprised me the most was the focus in high school textbooks on these incremental actions,” Wynes said. “Things like recycling and conserving water that are definitely positive steps to take, but once I realized how much more effective some of these other actions were, it was quite surprising to see them often not mentioned at all.”

As an example, they cited data from a Canadian textbook that said that using reusable shopping bags instead of plastic saves an average of 5kg of CO2 yearly.

Yet Wynes and Nicholas found that in terms of reducing one’s carbon footprint, using recyclable bags is less than 1% as effective as not eating meat for a year.

“Examples like this create the impression that the issue of climate change itself is trivial in nature, and represent missed opportunities to encourage serious engagement on high-impact actions,” the researchers wrote.

For those already interested in climate change, knowing how various actions compare is useful for making further lifestyle changes, Wynes said.

“A lot of people have been recycling for decades and they might be looking for the next step,” Wynes said. “Actions like recycling aren’t a place to stop, they’re a place to start and some other behaviors like eating a plant-based diet is four times more effective in terms of climate change.”

Read on to see how each of the four major actions stack up.

Have Fewer Children

It may be the biggest ask, but having fewer children can reduce emissions by 58.6 tons of CO2 emissions a year, as it also factors in the emissions that children themselves produce. That’s the same impact as 684 teenagers who comprehensively recycle for the rest of their lives.

Ditch Your Car

Living car-free can reduce emissions by 2.4 tons of carbon dioxide equivalents (CO2) — a term used to describe different greenhouse gases in a common unit — per year. If you’re not ready to completely forgo a vehicle, switching to a more efficient car can still save 1.19 tons of CO2 per year.

Avoid Air Travel

One roundtrip transatlantic flight can contribute 1.6 tons of CO2 emissions, meaning that skipping one flight is seven times as effective as recycling for a year. “I try my best to cut down on air travel,” Wynes said. “It can be tricky sometimes, but I’ve done it (by) replacing plane trips with train rides.”

Skip the Hamburger

Giving up meat entirely for a plant-based diet can reduce emissions by 0.82 tons of CO2 a year, making it eight times more effective in reducing emissions than upgrading light bulbs.