Two-thirds of the US population lives in metropolitan areas. That means urban centers account for much of the nation's greenhouse gas emissions.

But cities often fare better than their suburban counterparts when it comes to energy efficiency.

Last year's report by the Brookings Institution found the average American in a metropolitan area has a carbon footprint of 8.21 tons - 14 percent less than the average American living outside the city. City dwellers tend to live closer to where they work, shop, and play. And if they live in apartment complexes with five or more units, they
consume only 38 percent of the energy of households in single-family homes.

Kevin Surace is president and CEO of Serious Materials: "Getting people to live in an urban setting is a very, very green thing to do. When you heat your condominium, whatever heat is lost through your walls actually goes to the other people that are heating their condo at the same time."

Living closer can reduce carbon emissions. And new green materials can create manufacturing jobs as well as increased comfort in urban settings.