The Greenest Cities in America

When you think of a truly green lifestyle, you probably imagine a house deep in the countryside, far from the bright-lit city and suffused with nature. But when it comes to global warming, green acres aren't all that green — life in the crowded city is actually much more climate-friendly. For starters, the sheer density of urban life helps reduce one of the biggest sources of carbon dioxide emissions in the U.S. — transportation — compared to spread-out suburbs and rural areas, where driving is a must. Houses and apartments in cities tend to be smaller as well (sometimes much smaller, if you live where I live in New York), requiring less energy to heat, cool and power. City life may be dirty, it may be crazy — and it's definitely expensive — but in a carbon-constrained world, it's the greenest way to live.

A new report by the Brookings Institution, a Washington think tank, shows just how substantial the urban advantage is. Analyzing greenhouse gas emissions data from across the U.S., Brookings' scholars found that the average American living in a metropolitan area, as defined by the U.S. census bureau, had a carbon footprint of 8.21 tons of CO2 a year — 14% lower than the average American living outside the city. (In the interest of standardizing comparisons between cities, the Brookings researchers calculated emissions only from passenger and rail transportation, along with the energy consumption of residential buildings — which explains why their figures are considerably lower than the commonly cited per-capita footprint of 20 tons that takes into account the U.S. economy's total carbon emissions.) Given that the Kyoto Protocol calls upon developed nations to cut carbon emissions by an average of 5.2%, that 14% difference between the American city and the American countryside is significant. "This indicates that metropolitan areas are indeed places that we can look to for effective carbon reductions," says Marilyn Brown, a lead author of the report and a professor at the School of Public Policy at the Georgia Institute of Technology.

The Brookings report also points to the potential environmental advantage of moving away from the car-centric suburban development pattern and toward urban density — particularly as the U.S. population swells by 90 million between now and 2050. But not every city provides a great carbon model. The report ranks the top 100 metropolitan areas in the U.S. according to the sizes of their carbon footprints, and some of the results are surprising. Honolulu ranked No. 1, with the smallest carbon footprint of any U.S. city, while car-crazy Los Angeles came in second. (The city that has America's most extensive public transit network by far — New York — came in fourth.) Honolulu and L.A. got a boost from expensive power prices, which encourage conservation, while their pleasant climates further cut the need for energy-intensive heating.

Less surprising are the list's bottom-dwellers, including Louisville, Ky., and worst of all, Lexington, which feature little in the way of public transit and tend to be powered — cheaply — by carbon-intensive coal. The least green U.S. cities tend to be concentrated in the South and in the Midwest — the two regions where development is less dense on average, and the variable climate demands both heating and air conditioning. A city can't do much about its climate — L.A. will always have an advantage over New York — but its leaders can help encourage conservation, wider use of public transit and cleaner power. That last part makes a significant difference: the Washington, D.C. metro area, for example, ranks 89th; despite its extensive public transit network, the capital depends on coal plants for power. By ranking cities, says Daniels, "we hope to promote a virtuous competition that will stir solutions to the climate challenges we face."

That's a good idea. But the Brookings report is far from perfect. Honolulu proper may be green, but if researchers had considered that the city sits in the middle of the Pacific Ocean, and that a high proportion of its goods have to be delivered via plane or sea shipping — neither of which was counted in the Brookings report — it's unlikely the Hawaiian capital would be at the top of the table. Los Angeles' ranking might have been a little lower too if the city hadn't benefited from a census classification that seemed to include comparatively fewer commuters than New York. (The lack of apples-to-apples comparisons of carbon emissions between cities made the footprint rankings challenging, according to the report's authors.) Though Americans have always been ambivalent about urban life, it's clear that if we're going to control our carbon footprints, the city will be the place to be.