It’s no secret that cities produce fewer greenhouse-gas emissions per person than suburbs or rural areas — and some cities are better at keeping emissions down than others. Take New York City: Its dense urban structure and well-developed mass transit system keeps emissions well below somewhere like the sprawling and car-dependent Houston. But cities are more than just monolithic entities; factors like climate, manufacturing, car ownership, and wealth work differentially between cities and within city boundaries to influence greenhouse-gas emissions.

A review paper published in Environment & Urbanization dug into per capita emissions data for 100 cities from around the world to see which variables played a role. The paper’s authors also added a new twist by dissecting one city, Toronto, to see how rates varied neighborhood by neighborhood.

Zooming in from the national level to the city itself, the authors report that Toronto’s metro area has lower emissions than its home province of Ontario, which itself has lower emissions than Canada as a whole. The city itself fared better than the surrounding suburbs (not a big surprise). As they went further, they discovered enclaves of high per capita emissions even within the city center. The culprit? Wealth: Residents of tonier neighborhoods drove more and lived in older, less energy efficient housing, something preservation groups will surely be dismayed to hear.

The affluence story plays out on the global scale, too: Wealthy cities like New York, Beijing, Frankfurt, and London have much higher per capita emissions than poor cities like Dhaka in Bangladesh or Bangalore in India.

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But wealth isn’t the sole the offender. Climate is a large driver, but that’s not to say we should all ditch jackets and move to the Sunbelt. For example, Boston still has lower emissions rates than Austin and Philadelphia has lower emissions than Miami. A city’s source of electricity also plays a role, as do the qualities of its workforce. Cities like San Francisco and Portland can lay down such enviable carbon footprints because they tick those boxes in just the right way. Both enjoy mild climates that all but eliminate the need for air conditioning. Both are also heavily invested in the knowledge economy. San Francisco has particularly dense development, which reduces transportation emissions, while Portland gets a large portion of its electricity from hydroelectric power.

To encourage cities to trim their per capita emissions, the paper’s authors argue that governments should look to the success they had with solid waste reduction. While it’s true that many cities succeeded in reducing the amount of trash they send to the landfill, the comparison isn’t apt at this point. Cities pay to dispose of garbage; some do so handsomely. Currently, there’s no truly global price on carbon emissions. Never underestimate the ability of money to drive change.

There is some hope, though: Because urban areas produce a large portion of global greenhouse-gas emissions, city governments can take action that national governments have been hesitant to embrace.

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