Some metropolitan areas emit much more CO2 than others.

For many if not for most people, cities are inextricably associated with pollution. The image of the smoke belching industrial city is pretty firmly etched into the popular mind, while leafy suburbs and pastoral rural towns are generally seen as the epitome of a greener, Jeffersonian ideal. 

In reality, cities and metropolitan areas are key levers in energy conservation and the reduction of emissions and greenhouse gases.

Cities across the United States and around the world are embracing green strategies. They’re encouraging green building, energy conservation and recycling; they’re developing parks and green spaces; encouraging transit use, building bike lanes, and discouraging cars (some with congestion pricing efforts), and using walkability as a benchmark in their development and redevelopment efforts. The mayors of the global cities that make up the C40 have been among the most vocal and important proponents of action on climate change.  

This is auspicious, since metros account for an increasingly large percentage of the earth’s economic activity. Metro areas cover less than a third (29 percent) of the United States’ land mass, but house almost 85 percent of its population and produce 93 percent of its economic output. Across the world, metros with more than a million people house roughly one in five of the world’s people but account for more than half (52.3 percent) of its economic output. Metros of this size account for roughly three-quarters of economic activity in Asia, 60 percent in the emerging economies, and 54 percent in North America. 

How green are our metros? Not green enough. Global carbon dioxide emissions saw their biggest spike ever in 2010, The New York Times recently reported. Emissions rose 5.9 percent in 2010, according to an analysis released by the Global Carbon Project. The increase, amounting to a half-billion extra tons of carbon dumped into the atmosphere, "was almost certainly the largest absolute jump in any year since the Industrial Revolution, and the largest percentage increase since 2003."

But if the cloud (no pun intended) has a silver lining, it’s this: Not all cities are the same. In fact, our biggest cities tend to be among our cleanest.  

With the help of my Martin Prosperity Institute colleagues Kevin Stolarick and Charlotta Mellander and José Lobo of Arizona State University, I decided to look at the geographic variation in emissions across U.S. metros, something we can do thanks to the databases at Project Vulcan

Funded by the National Air and Space Administration (NASA) and the Department of Energy (DOE) under the North American Carbon Program (NACP) and involving researchers at Arizona State University, Colorado State University, and the Lawrence Berkeley National Laboratory, Project Vulcan provides a detailed inventory of CO2emissions from a variety of sources – houses, cars, factories, utilities and so on across 355 U.S. metros. We developed several basic measures of emissions to control for the size and scale of metro areas, examining the level of emissions on a per capita basis, per worker, and per the level of economic output (Gross Metropolitan Product). The maps below, by the MPI’s Zara Matheson, chart each of these measures.

The first map (above) charts CO2 emissions per person. The geographic variation is considerable, from a high of nearly 70 tons per person to a low of less than one. The highest emissions per capita are in smaller industrial cities and metros – Farmington, New Mexico (69 tons per person); Steubenville-Weirton, Ohio-West Virgina (54 tons per person); Flagstaff, Arizona (45 tons per person), and Monroe, Michigan (45 tons per person). Small college towns and resort destinations, such as Naples, Florida, and Corvallis, Oregon, tend to have the lowest levels of emissions.

Large metros (those with more than one million people) have relatively low levels of emissions per capita as well. New Orleans produces 7.8 tons of emissions per person, ranking in 59th place overall. Cleveland is 61st and Louisville 62nd with 7.4 tons per person each. Only four additional large metros rank in the top 100 – St. Louis at 73rd (about the same as Madison,Wisconsin), Cincinnati at 75th, 77th place Houston, and Kansas City at 83rd. Eleven large metros rank among the 100th to 200th, and another eight rank between 200th and 300th. Twelve large metros – including New York, (2.3 tons per person), L.A. (1.8 tons), San Diego (1.9 tons), Phoenix (1.9 tons), Washington, D.C. (2.3 tons), Miami (2.2 tons) and Seattle (2.2 tons) – rank among the 50 lowest emitting metros. It’s notable how well super-large metros (those with more than three million or even five million residents, like New York and L.A.) do on these rankings.

The second map (above) connects CO2 levels to the workforce, charting the level of CO2 emissions per worker. Again, there is considerable geographic variation. The largest emitters produce more than 150 tons of CO2 per worker, while the lowest produce just 2 or 3 tons per worker. Large metros perform even better on this measure. Los Angeles and San Diego ranked among the ten lowest emitting metros, with Raleigh, Washington, D.C., Phoenix, Portland, Oregon, and Seattle among the 25 lowest emitting metros. Most large metros rank among the 100 lowest emitting metros nationwide.

The third map charts the level of CO2 emissions per millions of dollars of economic output (or Gross Metropolitan Product). The geographic variation is again quite considerable, with the largest emitters generating between 1,000 and nearly 2,000 tons of emission per million dollars of output, and the lowest emitters producing just 25 to 50 tons. Large metros perform especially well on this metric. Washington, D.C., Seattle, L.A., and San Francisco number among the five lowest emitters in the nation, with Bridgeport-Stamford, San Diego, and New York making the top ten, and another dozen or so ranking among the 40 lowest emitters.

We find that larger metropolitan areas are therefore relatively efficient regardless of their size, geography, age, and industrial composition. That’s because large metros share qualities like scale, density, and clustering of their populations and economic activities, which play a substantial role in reducing emissions and shaping their relative greenness.

My next post takes a closer look at the connection between greenness and city size.

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