Houston won this year's U.S. Conference of Mayors Climate Protection Award. Houston -- the city that serves as headquarters for BP America, ConocoPhillips, Halliburton, Marathon and Shell, all within its 580 square miles.

Don't act so surprised, Mayor Annise Parker told HuffPost.

"The City of Houston has been a leader in green energy for a very long time," she said. "I like to say that if you're going to do missionary work, you have to go where the non-believers are."

The mayors' association gave Parker the award along with Mayor Elizabeth Tisdahl of Evanston, Ill. Houston was cited in particular for its green buildings programs, which are retrofitting all 262 city-owned buildings and providing funding for private owners to do the same.

The City of Houston is also the largest municipal purchaser of renewable energy in the nation, according to the Environmental Protection Agency. It helps that Texas generates more megawatts of wind power than any other state, including California.

Parker said that when she brings her clean energy gospel to the executives of oil and gas companies, they don't laugh.

"No one -- you have to understand -- no one in the oil and gas industry is afraid of the oil and gas market going away. We take the longer view that oil and gas is going to be with us for a very long time, but growing beside it is going to be the renewable energy market."

Houston is still among the five worst carbon emitters in America. The city spreads further than the eye can see, and commutes are long. It is also hot and muggy, so greenhouse gas emissions from air conditioning are worse than in more temperate "horizontal" cities like Los Angeles.

The average New Yorker emits 7.1 tons of greenhouse gas in a year, but the average Houstonian emits 19.3 tons. Those numbers come from a paper being drafted by Dr. Patricia Romero-Lankao and her colleagues. She studies the intersection of urban development and climate change at the Institute for the Study of Society and Environment in Boulder, Colorado.

Romero-Lankao said that Houston's focus on energy efficiency was "a smart decision, but is not enough. Actions aimed at addressing urban form and density are equally important."

While some Houstonians may live a life of shuttling between over-air-conditioned house and over-air-conditioned office, at least a few are taking to the city's 7 miles of light rail, which expand to 32 more by 2014.

Deron Lovaas, the transportation policy director for the Natural Resources Defense Council, was a judge for the climate protection award.

He said the U.S. Mayors' Conference picked Houston because out of the many cities that have plans to reduce carbon emissions, it is one of a few that are taking concrete steps.

The choice, he said, "hopefully provides a model for other southeastern cities, or other southeastern mayors, and gives them some indication that they don't have to be Portland or Manhattan in order to turn around and become more sustainable."