GREEN GHERKIN: This London skyscraper uses 50 percent less energy than a conventional office building.

Our homes and offices account for more than one third of all greenhouse gases emitted by human activity—the bulk of it for heating in winter and air-conditioning in summer, according to the U.N. Intergovernmental Panel on Climate Change (IPCC).

Taking simple steps such as caulking windows, installing thicker insulation and double-paned windows, and using energy-efficient appliances can cut the energy used in a given building by as much as 50 percent. In fact, such energy-saving measures in the U.S. alone could negate the need for 66 large coal-fired power plants, according to a study by McKinsey Global Institute, an economic think tank and global consultancy.

"Just tightening up the air leakage [insulating and caulking] could get you up to 40 percent in energy savings," says Robert Moran, national sales manager of building envelopes at chemical giant BASF.

Yet, only 2 percent of commercial real estate and 0.3 percent of new homes are considered to be "green buildings"—defined as "environmentally preferable practices and materials in the design, location, construction, operation and disposal of buildings," in a 2008 report by the Montreal-based Commission for Environmental Cooperation (CEC). The CEC is an international organization established by Canada, Mexico and the U.S. under the North American Free Trade Agreement (NAFTA) to address continent-wide environmental issues.

Still, from the Bank of America building in Midtown Manhattan that boasts recycled and renewable construction materials to the Olympic edifices in Beijing, like the Aquatics Center that captures rainwater, greener buildings are beginning to rise.

Slide Show: A Magnificent Seven