Adding features like solar generators or solar water heaters can pay for themselves over a longer term as well. "I think residential is a slam dunk," Levine says. "It's just a matter of applying technology that we already have."
Another area where cities can play a major role in warding off warming is waste management, enhancing efficiency by taking relatively cheap and simple steps such as capturing the latent power in landfills or recycling. "Things like waste recycling or waste minimization actually avoid greenhouse gas generation," says waste management expert Jean Bogner, a lead author of the IPCC report. For instance, making a beverage can from recycled aluminum uses only 5 percent of the energy it would take to create one from scratch. "If you recycle in the case of aluminum, you are talking about a 95 percent savings of energy," says IPCC author Lenny Bernstein, an environmental consultant.
The bottom line: buildings contribute a tremendous amount of GHG emissions whereas garbage produces relatively little (roughly 5 percent, according to the IPCC), but both offer immediate cost-effective remedies for climate change. A key to limiting global warming will be making sure that cities from New York to Addis Ababa implement those changes. "Now is the time to start doing real work," says Ken Livingstone, mayor of London. "Retrofitting our buildings and bringing down our carbon emissions."