The 50 largest cities in the United States are at least thinking green, according to the 2008 SustainLane U.S. City Rankings released Monday.

SustainLane ranks the cities in 16 different economic, environmental and clean-tech categories.

"The SustainLane U.S. City Rankings speak ... to the local leadership found across America and how mayors, city councils and their offices of sustainability are preparing their cities for resource deficits due to high gas and energy prices, drought, rising food prices and other issues," said James Elsen, the CEO of SustainLane Media, in a press release.

This year, SustainLane found trends that helped raise municipal scores across the board. One of the biggest is the general mainstreaming of the green movement. City administrators nationwide are considering the sustainability of their cities, appointing sustainability offices, creating climate change plans and mandating green municipalities.

The top five cities this year are Portland, San Francisco, Seattle, Chicago and New York.

The full report is available on the SustainLane website. The 2008 City Rankings will be featured at the world's first green cities and communities conference which begins Oct. 1 in Geneva, Switzerland. SustainLane started publishing its ranking reports in 2005. Since then, SustainLane has seen both median and average scores increase significantly.

Image — SustainLane