Latest News

Study: Dense cities have smallest carbon footprints

People living in urban-core cities with dense housing and mass transit do a better job of controlling excess carbon emissions, according to a new study released today by the Brookings Institution. And big — at least when it comes to cities — is not necessarily bad.

Seems that when we humans stretch out a bit, in the form of sprawl, our activity tends to emit more carbon dioxide and other greenhouse gases.

"Americans are driving more, building more, consuming more energy and emitting more carbon," the report states. "Rising energy prices, growing dependence on imported fuels and accelerating global climate change make the nation's growth patterns unsustainable."

The report, Shrinking the Carbon Footprint of Metropolitan America, calls on the federal government to establish policies to expand transit options, make regional freight operations more energy-efficient, encourage energy-efficient retrofitting of homes and employ other strategies to decrease urban impact on the environment.

What's a carbon footprint?

It's a way to assess the effect people have on the environment by measuring the greenhouse gases our activity produces, typically in units of carbon dioxide. It is sometimes used to measure the effect that human activity has on global warming.

Six interesting findings


Metropolitan centers are home to two-thirds of Americans and provide 3 in 4 jobs, but they were the cause of only 56 percent of emissions from residences and transportation in 2005. (People who live downtown put fewer miles on their vehicles, are more apt to have mass transit available and tend to use less electricity.)


West is best. All but one of the 10 largest per-capita emitters are east of the Mississippi River. From 2000 to 2005, the carbon footprint in the western U.S. actually decreased. Texas did not have a metropolitan area in the worst 40 cities on the list.


Carbon dioxide accounts for 84 percent of the greenhouse gases emitted in the U.S. and comes primarily from energy used in buildings and transportation. Emissions from residential, commercial and transportation sectors have increased by more than 25 percent over the past 25 years. They are expected to grow by 16 percent between 2006 and 2030.


Transportation must become less dependent on petroleum-based fuels, and the best minds must tackle the development of clean-energy and low-carbon technologies. Denser development and rail transit tend to be part of the big-city makeup. On the other hand, low-density areas such as Nashville and Oklahoma City are among the 10 largest emitters.


Areas with high freight traffic tend to perform less well — because of trucks.


Although China overtook the U.S. and Europe in 2006 as the biggest emitter, the U.S. is still a carbon-intensive nation.

Where the Metroplex ranks

Arlington-Dallas-Fort Worth ranks 57th out of 100 major U.S. metropolitan areas. El Paso was the best in Texas, ranking No. 9. San Antonio was No. 33, greater Houston was No. 35 and the Austin area was No. 55.

The Metroplex's carbon footprint decreased 11.05 percent from 2000 to 2005. That includes a 14.6 percent decrease in the transportation sector alone. In the same period, Dallas' residential carbon footprint decreased by 6.4 percent. This compares favorably with an overall 2.2 percent increase in carbon footprint nationwide.

Marilyn A. Brown, one of the report's authors, was careful to qualify the results in individual metropolitan areas, noting that the study looked at transportation and residential carbon emissions only. In addition, 2000 data is less reliable than 2005 data. Updates of the study should be more accurate.

The best and the worst

Honolulu, greater Los Angeles and greater Portland, Ore., had the smallest carbon footprints. The biggest footprints were in the Lexington, Ky., area, Indianapolis and greater Cincinnati. The best performers had dense development and mass transit. The worst performers had sprawl issues and little or no mass transit.

Does rail make a difference?

Yes, says Robert Puentes, a transportation expert with the Brookings Institution, because of subsequent development around transit stations. Rail lines create "high-density nodes" where growth can occur. (Think Mockingbird Station in Dallas.)

"As the nation accommodates the next 120 million people, those places with rail can do it in a much more compact form," Puentes said.

Proposed goals

The study proposes that the federal government undertake these actions:


Put a price on carbon to account for the external costs of fossil fuel combustion.


Step up investment in energy research and development.


Establish a national renewable electricity standard.


Help states to reform their electricity regulations.


Improve information collection and dissemination on emissions and energy consumption.

Making it law

On Wednesday, the report authors and other Brookings colleagues identified the embattled Lieberman-Warner Climate Security Act and the 2009 federal highway/transit reauthorization as two possible vehicles for instituting some of their proposals.


BRYON OKADA, 817-390-7752