What are the best ways to shrink your carbon footprint?

Emma Rohmann works hard to minimize her family's contribution to climate change. She and her husband Erich, who have two young children, have retrofitted their Toronto home to be more energy efficient. They've also cut way back on eating meat, driving and flying to reduce their carbon emissions.

"Thinking about the future I'm leaving for my kids, I think my carbon footprint is something I worry about a lot," says Rohman, 33, an environmental engineer who runs Green at Home, a consulting firm that helps families and businesses make greener choices.

As the annual UN climate change conference wraps up in Bonn, you might be thinking about that too, and wondering whether you're doing the right things to reduce your carbon emissions.

But you can't do everything, and it can be difficult to figure out which choices will have the biggest impact.

Carbon footprint science

That's where science comes in.

Studies show that Rohmann's choices will definitely make a difference, but there's probably more she can do.

Scientists have done calculations and published hundreds of studies showing how much impact personal actions and choices can have.

For example, one compilation of studies shows eating organic doesn't make much of a difference, but going vegetarian will have a huge impact.

Another recent study shows feeding your dog or cat a low-protein diet may help, and another shows that whether switching from a gas or electric car decreases or increases emissions depends on which province you live in and therefore what kind of energy is used.

It can be hard to compare so many studies, so earlier this year, researchers at the University of British Columbia compiled data from dozens of studies to calculate the emissions from individual behaviours.

They found the four things that would have the biggest impact were:

- Having one fewer child (which could reduce emissions by 58.7 tonnes of carbon per year, due to the absence of emissions that an extra person would generate over a lifetime).

- Living car-free (reducing emissions by 2.4 tonnes per year).

- Avoiding air travel (reducing emissions by 1.6 tonnes per transatlantic flight).

- Eating a plant-based diet (reducing emissions by 0.8 tonnes per year compared to a diet that includes meat).

Lead author Seth Wynes compared those to actions recommended by sources such as governments and high school textbooks and was surprised by how different they were.

"They tended to focus on incremental behaviours instead, with smaller step-by-step benefits," Wynes said, like conserving energy through hanging clothes to dry or improving home heating and cooling efficiency.

'Easiest and most tangible'

But there are reasons why Rohmann, who advises clients how to live more sustainably based on recommendations from the government and from environmental organizations, targets energy conservation and home heating and cooling first.

That's followed by reducing waste — "because our landfills produce methane, which is a more harmful greenhouse gas than carbon dioxide." It's a good tip. Wynes found eliminating food waste could reduce your emissions by 0.37 tonnes per year — more than energy conservation.

Finally, Rohmann also suggests reducing meat consumption and car use.

Those are her top four recommendations because they're the "easiest and most tangible for people to implement fairly easily." They also tend to save money.

But while they don't match up exactly with Wynes's list, Keya Chatterjee, who has pored over dozens of scientific studies like the ones Wynes compiled, says there's also something to be said for emphasizing energy conservation and improving home heating and cooling.

"Behaviours are actually much harder to change than technologies," said Chatterjee who is the executive director of the U.S. Climate Action Network. When her son Siddarth was born in 2010 she studied the carbon footprint of lifestyle choices in detail, in an effort to keep her family's footprint the same while adding a person. She wrote a book on the topic, The Zero Footprint Baby.

Automated savings

Switching incandescent bulbs to LEDs may not make a huge difference to your carbon footprint, but it makes a difference in a long-term, automated way, said Chatterjee, executive director of the U.S. Climate Action Network. And some technology switches, like changing to a smaller, more efficient fridge or from a gasoline-powered car to an electric one — or especially to a bike — make a bigger difference.

Chatterjee found from her experience that behavioural changes are more difficult.

So did Rohmann.

"For my German, meat-loving husband, reducing meat consumption was probably the toughest," she said. On the other hand, reducing air travel was easier than she thought once she decided to do it.

Wynes acknowledges his recommendations aren't likely to move adults with established lifestyles. But climate change is a huge problem, he added, and recommendations to young people on how to tackle it need to be big, too.

"We've been talking with students about things like recycling and changing light bulbs for years and perhaps decades," he said. "Now is an important time to start scaling up."

In the meantime, if you're confused about how to reduce your carbon footprint, don't be, says Chatterjee. Really, you only need to make one choice: "Get off fossil fuels."