Cities can play a major role in the global effort to curb climate change, a new report says—and a major step they can take is helping their inhabitants consume a whole lot less stuff by making changes in the way cities are run.

Even the most forward-thinking cities have a long way to go to neutralize their carbon emissions, the report says. That’s partly because for years, cities have been doing carbon math wrong, adding up only the carbon costs that occur within city limits. But much of city dwellers' climate impact actually comes from the things they eat, use, or buy that originate far outside the city—from food to clothes to electronics and more.

To keep emissions in check, the report suggests, cities should aim to trim their carbon emissions by 50 percent in the next 11 years, and then by a total of 80 percent by 2050. And because, as the researchers found, a hefty portion of those emissions can be traced back to consumer goods, food, and energy produced outside city limits, one of the best things cities can do is help their residents pull back on consumption.

That’s a big challenge but also a big opportunity, says Mark Watts, the lead author of the report and executive director of the C40 city network, an international network of cities committed to addressing climate issues.

“Halving emissions in the next 10 years--that’s what needs to happen, and cities see that,” he says. “Now, it’s time to move onto the next stage, because we’re already in a climate emergency, and figure out how does government have to change in order to hit that target?”

The true cost

Today, some 55 percent of all humans live in urban areas, where they account for about 70 percent of all annual carbon emissions. In the future, demographers predict, even more of Earth’s population will likely congregate in cities, hitting about 70 percent by 2050. If nothing changes, carbon emissions from cities is on track to almost double by 2050, the report says. And as cities’ carbon emissions go up, so do the planet’s.

But city dwellers—especially those in wealthy cities in developed countries—tend to buy more, fly more, and use a lot more energy than people who live in rural areas. All the things they buy—from the clothes to the food to the electronics and more—have their own complicated and often substantial planetary costs that aren’t always immediately obvious.

A t-shirt, for example, might get made of cotton grown in India; be manufactured in China using coal energy to power the sewing machines; packed up in yet another country with oil-based plastic packaging; shipped across oceans in fossil-fuel-fired container ships; and delivered by diesel truck to the store in which they’re sold.

A real assessment of someone’s carbon footprint takes the carbon footprint of these “consumed” products into account. And when city dwellers’ consumption habits are added up, it turns out that urbanites have a carbon toll about 60 percent higher than previous calculations suggested. City dwellers in 96 of the world’s biggest cities alone make up a hefty 10 percent of all global carbon emissions each year.

“People tend to forget that most of the products we consume and our personal carbon footprints are imported from elsewhere to give us a great life in the modern cities we live in,” says Jeroen van der Heijden, an expert on climate and government at Victoria University in New Zealand.

“If we truly want to make a meaningful contribution to cutting carbon emissions, we must do much better than building green houses. We have to rethink how we live and what we consume.”

The road ahead is paved with less stuff

National governments and international communities have struggled to take meaningful steps toward addressing carbon emissions. In many cases, cities have stepped in to fill that role, developing ambitious climate action plans that seek to curb emissions.

The C40 network cities have collectively pledged to limit their carbon emissions to levels that will help keep the planet from warming more than 1.5 degrees Celsius (2.7 degrees Fahrenheit), the upper limit of warming the Intergovernmental Panel on Climate Change recently warned against exceeding.

To get there, the report suggests cities can nudge behaviors in six key areas: food, construction and building, clothing, vehicles and transportation, aviation, and consumer electronics from washing machines to computers to phones.

For example, cities are often already major food purchasers; they buy for schools, city organizations, and more. That means that they can influence emissions by changing their buying practices.

New York schools are starting a “Meatless Mondays” program in 2019 that the city says will reduce its citizens' carbon footprint and make kids healthier. Other cities, like Milan, have put programs in place to help local agriculture thrive, reducing the carbon costs from transporting foods long distances.

It turns out that city dwellers also buy a lot of clothes, and the carbon impact of those jeans and sweaters piles up. If people bought only eight new clothing items each year, the report says, they could cut that impact in half.

Cities can also take action to reduce the amount of energy their denizens use by doing things like tweaking building codes to encourage retrofits of buildings rather than new construction; prioritizing low-carbon transportation options that keep people from buying new cars or motorbikes; and setting up programs that help people extend the lifetime of their electronics and appliances rather than constantly replacing them. Every intervention that helps people buy less new stuff adds up, pushing a city's emissions down.

The transformations have to happen in a way that cuts from the individual consumer all the way up to the big players like the utilities who serve a city, says Patricia Romero-Lankao, an expert on cities and the environment at the National Renewable Energy Laboratory in Colorado.

“Yes indeed we need to change the way we use energy, heat houses, think of our sense of comfort—which is a cultural thing—buy clothes, all that,” she says. “But we really also need to work with the utilities, the corporations, the big players whose products we’re using.”