Big city with the lowest emissions - Los Angeles?!

There's a new report out from the Brookings Institution ranking the country's 100 largest urban areas by carbon emissions from transportation and residential energy use (The New York Times article here, rankings and graphics here). Some of the results are pretty surprising, but the report only gives numbers, not explanations. Here are the top ten:

1 Honolulu, HI
2 Los Angeles-Long Beach-Santa Ana, CA
3 Portland-Vancouver-Beaverton, OR-WA
4 New York-Northern New Jersey-Long Island, NY-NJ-PA
5 Boise City-Nampa, ID
6 Seattle-Tacoma-Bellevue, WA
7 San Jose-Sunnyvale-Santa Clara, CA
8 San Francisco-Oakland-Fremont, CA
9 El Paso, TX
10 San Diego-Carlsbad-San Marcos, CA

At first glance, the West Coast and Southwest (including Texas) seem to be doing quite well, the Midwest and South are doing badly, and the Northeast is in the middle. As someone in the habit of demonizing sprawl "cities" like Houston, Phoenix, Las Vegas, and the concrete desert of southern California, this was a bit disorienting. Could it be that, as The New York Times article emphasized, a warm climate that obviates the need for heating is a better way to reduce emissions than compact, mixed-use cities? Don't the first three use huge amounts of energy on air conditioning? Does it make sense to build cities in the desert if it'll fight global warming?

In fact it's not nearly that simple, as indicated by the inclusion of Chicago, New York, and Boston (none of which are known for their mild winters) in the top quintile. Those cities' high density and good (for the US) transit systems help them compete with the sprawling cities of southern California and the Southwest, but that doesn't fully account for the results either.

First we have to separate transportation and residential energy. The helpful maps included in the report show that warm-weather states dominate the top quintile of residential energy use - which also includes New York - while the second quintile is evenly split between southern states and the Northeast (plus Chicago). Heating is certainly a factor, but power sources seem at least as important. Those states with low emissions rely to an unusual degree on nuclear, hydroelectric, and/or geothermal power for electricity, none of which produce carbon emissions, while those with high emissions correspond closely to the country's coal belt. (See the government's figures on energy consumption by source and by state here.)

Since nuclear and hydroelectric power both have serious drawbacks, it's not at all clear how far these emissions numbers get us toward finding green models to follow. More useful might be total per capita energy use, which you can see graphically on the maps at Nationalatlas.gov (go here, click People > Energy consumption > Residential energy per capita, then Redraw map to see use by states). Here we can see that warmer states do use less energy, but much of the Northeast uses a similar amount, while the heaviest users include both cold states and southern states like Alabama and Mississippi. I don't have any explanations for these patterns, but it would be worth looking into it to figure out the best policies for reducing energy use.

The transportation numbers, with fewer variables involved, are a bit more straightforward. Dense cities with transit networks perform the best, which means the Northeast is the hands-down winner (except for Trenton, which is dead-last in car emissions). Other winners are Los Angeles (#5), Philadelphia (#6), Portland (#10), Cleveland (#12), and Chicago (#17). The bizarre spectacle of LA ranking better on highway emissions than places like Philly and Chicago is explained by the fact that LA has very little freight traffic, so trucking emissions drag Chicago and Philly down even tho they beat LA easily when only car emissions are considered. Still, LA remains in the top 20 on cars so clearly there is a fair amount of transit use and population density is not nearly as low as many other cities. How Houston (#31) managed to beat much denser cities like Minneapolis (#37) and St Louis (#75), I have no idea.

In the end, the report reminds us that carbon emissions are spread unevenly across the country - a result primarily of differences in density, the quality of transit, and the source of electricity. It raises the difficult question of whether we should be expanding nuclear power to reduce carbon emissions. And it shows yet again that public transit is one of the best ways to fight global warming.