Calculating the Biggest Climate Behavior Change Wins Doesn't Start with Individuals

If you are admitted to a New York City public hospital, the in-patient meal menu might surprise you: It’s filled with items like a veggie pad Thai and a Moroccan vegetable tagine. The options look so tempting you probably wouldn’t notice the missing meat and dairy.

Four years ago, NYC Health and Hospitals made plant-based foods their default inpatient meal. Animal products are still offered, but only by request.

This seemingly small change has made a big impact. Since March 2022, more than 2.8 million plant-based meals have been served, cutting food-related carbon emissions by 36% and trimming costs by 59 cents per meal, all while keeping patient satisfaction ratings at 98%.

This one change to a hospital procurement policy had a bigger impact than a large media campaign aimed at asking individuals to change their diets likely could have. People's choices are shaped, more than they realize, by the systems around them: the rules, incentives and defaults that structure daily life. That’s why systems have the power to shift behavior, and this potential goes beyond food.

If everyone adopted climate-friendly behaviors like driving EVs, using renewable energy at home or eating less meat, the world could eliminate most of the greenhouse gas emissions warming the planet. Reshaping the systems behind those choices is key to transformation at scale.

WRI research found that when individuals try to change behavior without supportive systems, they only unlock about 10% of the emissions reductions theoretically possible. This is because individual action alone only goes so far. Taking the bus instead of driving makes a real difference, but without reliable, frequent transit, that effort stays stuck near 10%. The other 90% depends on more institutional decisions that make low-carbon choices easy, affordable and, ultimately, commonplace.

Those institutional decisions are usually made by city planners, policymakers and industry leaders, whose choices affect millions of people. Yet they often lack the actionable insights needed to direct their finite resources toward the sustainability initiatives that will have the greatest impact.

So which interventions actually move the needle? To help decision-makers answer this question, WRI created a calculator that compares the projected emissions-reduction impact of programs and policies meant to encourage low-carbon behaviors. Unlike popular personal carbon calculators that tally the climate cost of just one person's choices, this new tool measures the potential impact of decisions that affect millions.

Here’s how decision-makers can calculate which climate behaviors will have the biggest impact:

Step 1: Decide Which Behaviors Matter Most

Our research shows that not all climate actions are created equal, and the differences between climate actions are much bigger than people realize. For example, one person giving up their car has the same climate impact as 77 people composting their trash. Eating less animal protein has more than triple the emissions impact of reducing food packaging. And installing solar power at home is twice as impactful as reducing your energy use (by switching off lights, for example).

Imagine a credit card provider is reworking its rewards program to drive climate-friendly behaviors. (It’s worth noting this is not just theoretical, some companies have already been experimenting via small pilots with these types of rewards.)  Should it offer bonus points for purchases at plant-based restaurants, or for composting-service subscriptions? Both are trackable food-related purchases. But shifting plant-based eating cuts emissions 11 times more than composting.

Maybe a company wants to encourage employees to drive less. Should it reward public transit card use or carpooling? Both reduce car trips but shifting people to public and active transport has nearly twice the emissions reduction impact as shifting to carpooling.

These are not marginal differences. If the credit card company rewards plant-based restaurant purchases instead of composting subscriptions, and just 10% of its 1.1 billion cardholders shift their behavior, that is the difference between 36 million metric tons of emissions reduced per year and 3 million. Same program. Same budget. But a 30 million metric ton difference — equivalent to taking almost 7 million cards off the road.

Step 2: Pick the Right Tool 

Once you know which behaviors to focus on, the next hurdle is enabling adoption.

Behavioral interventions use a range of tools to support shifting to new behaviors. We bucket these into six categories: providing enhanced information, providing feedback, offering incentives, eliciting commitments, leveraging social norms and applying choice architecture that simplifies decision-making (for example, by providing defaults, like NYC Hospitals did). These tools can be used alone or in combination.

Here too, the data shows that some approaches work better than others.

Across the studies we analyzed in our recent report, we found that choice architecture (such as putting more sustainable options front and center) and commitment devices (like signing up for a bikeshare membership) are among the more impactful tools. Meanwhile, enhanced information approaches (such as personal carbon footprint calculators and marketing campaigns) are, on average, among the least.

Two important notes on using these tools to estimate behavioral outcomes:

When information is genuinely new, it can punch above its weight. For example, most people don't know that recent advances have made plug-in balcony solar panels significantly cheaper and easier to install than rooftop solar. An information campaign delivering this news that these systems are now legal in many U.S. states could outperform what the average data suggests.

On incentives: the studies behind these estimates generally tested small incentives. Incentives that can make large purchases like electric vehicles or heat pumps dramatically more affordable would likely have a substantially greater impact.

How This Works in Practice

Let's revisit the credit card company scenario: If the company decides to reward plant-based restaurant purchases over composting — as this offers 11 times greater emissions reductions — which tool should the company use to help its customers shift to more plant-based purchases?

While a business could choose from any of the six tools, for illustration let’s narrow in on providing enhanced information and applying choice architecture. Assuming the credit card’s efforts will reach 1 million people, here are what the two scenarios could look like based on existing evidence:

1) Providing enhanced information, like an email blast on the climate benefits of plant-based eating, would have an expected behavioral shift of 6 percentage points on average. Meaning that for every 100 people exposed to the campaign, about six more people change their behavior than would have otherwise.

In the credit card scenario, if 100 million cardholders received the email, then approximately 6 million would likely shift their behavior, resulting in carbon dioxide (CO2) reductions of more than 2 million metric tons per year. That’s equivalent to taking almost half a million cars off the road every year.

Or

2) Applying choice architecture, like auto-enrolling cardholders into a "Green Rewards" tier with double points for plant-based restaurant purchases, would have an expected behavior shift of 14 percentage points. If 100 million cardholders were auto-enrolled, that’s approximately 14 million people likely to shift their behavior, which is a projected emissions reduction of approximately 5 million metric tons of CO2 per year — equivalent to taking over 1 million cars off the road every year.

Explore the Calculator

Beyond what you eat or how much you fly, transformative impact comes from the households, teams and communities that your decisions reach.

Even if you’re not a policymaker or the head of a credit card company, your choices still have significant reach. You might be the head of your household whose decisions impact your family, or the owner of a small business, or perhaps part of a sustainability club and want to decide which activities to focus on.

The calculator below can help you, too.