Which U.S. Cities Contribute Most to Global Warming?

If you care about reducing your emissions of greenhouse gases, then you might want to move to Honolulu, Los Angeles or Portland, Ore., according to a new study from The Brookings Institution. These three metropolises boast, respectively, the lowest three per capita levels of world warming pollution (read: carbon dioxide) in the nation's top 100 metro areas.

"Large metropolitan areas give their inhabitants smaller carbon footprints," says energy policy expert Marilyn Brown of the Georgia Institute of Technology in Atlanta (ranked 67th), lead author of the study. "Footprints are the smallest in areas with high density and good rail transit."

"Shrinking the Carbon Footprint of Metropolitan America" examined fuel use in transportation and energy use in homes, landing, from fourth to 10th ranking, New York City; Boise, Idaho; Seattle; San Jose, Calif.; San Francisco; El Paso, Tex.; and San Diego.

But the survey did not take into account key municipal contributors such as commercial buildings and industry—or transportation other than that on highways, thereby neglecting the carbon output of the air freight resupply on which Honolulu relies. The researchers also used the U.S. Census Bureau's metropolitan boundaries, allowing cities like Los Angeles to avoid having the carbon emitted by its legions of suburban commuters count against its total. Weather played a role as well. Cities in moderate climes fared better than those whose residents must expend more energy to cool and heat their homes.

The report, the first of its kind, reveals that southern and eastern cities contribute most to climate change. The reason: residents there rely more on coal and cars than denizens in other parts of the country. "The nation's carbon footprint has a very distinct geography," Brown says. "Those who live in an area relying on coal and gasoline are likely to see a large increase in energy costs. There is a business and economic vulnerability that these metropolitan areas have."

The residents of Lexington, Ky., Indianapolis and Cincinnati emit the most greenhouse gases—nearly 2.5 times as much carbon on a per capita basis as their peers at the top of the list with smaller footprints. But these cities have the added burden of being major regional transportation hubs; in other words, their per capita emissions burden is skewed upward by the freight needs of the rest of the country, according to senior research analyst Andrea Sarzynski at Brookings (based in Washington, D.C., ranked 89th).

Rounding out the bottom 10 biggest emitters per capita are: Knoxville, Tenn., Harrisburg, Pa., Oklahoma City, St. Louis, Nashville, Louisville, Ky., and Toledo, Ohio.

The report authors say the goal of the study is to show cities how to reduce emissions by taking a page from those already keeping a lid on them. The research also demonstrates that city dwellers in general are faring better than their country (or suburban) cousins, because of mass transit and densely packed populations in smaller areas.

But despite climate change warnings, city emissions continue to rise, creeping up by slightly over 1 percent per year since 2000. Environmental scientist Martin Parry at the University of East Anglia in England and the U.N. Intergovernmental Panel on Climate Change warns this week in Nature Reports Climate Change that the trend must be reversed and emissions slashed by at least 80 percent to avoid the worst effects of global warming.

The study authors recommend that the federal government put a price on greenhouse gas emissions, establish a national renewable energy standard and, also, fork over funds for research and development of new energy sources. "Energy R&D should be in line with health care and national defense in terms of spending," Sarzynski says. "The feds really seem to be behind."

The report also calls for reform of existing federal policy, including a shift from funding highways to mass transit and realigning the mortgage interest deduction so as to no longer reward those who purchase the largest and most energy-wasting homes. "Metropolitan regions and the built environment are often neglected when talking about solutions [to global warming]", Brown adds. "They are major emitters and they are poised to be part of the solution."