Climate change, locally Cutting emissions also requires rethinking the way cities are designed, built and managed.

The time for debate is over. Climate change is real, and the results of inaction will be nothing short of catastrophic. Avoiding its most disastrous effects will require that we cut emissions severely - by a full 80 percent by 2050, according to scientists worldwide. We're not going to achieve cuts that deep with a few solar panels and hybrid cars. The fact is, achieving hefty reductions will require that we rethink the way we design, build, and manage our communities.

Climate legislation from Washington is desperately needed, but our eagerness for national policy should not distract us from the equally pressing need for our towns and cities to take a leading role. About a quarter of our greenhouse emissions are the result of home energy use. Transportation accounts for an additional third. And the policy arena that most directly shapes these two aspects of our lives is largely local.

So, where do we start? With the past. Our communities used to be just that, communities. They included shops, businesses, and homes in an integrated village, town, or city. It turns out, this way of building communities not only fostered a greater sense of citizenship it was also highly energy efficient. Yet, over the past half century, we have torn apart our communities, separating homes and businesses, rich and poor, into discrete zones separated by miles of highway.

The effect has been a dramatic increase in the energy intensity of our everyday lives. Picking up a quart of milk is no longer just a walk to the corner store; it's a 10-minute drive in a 6,000-pound vehicle. The result is not only a changing climate, but also a steady spread in the average American's girth.

Across the country, new town centers are being developed that allow people to reduce their impact on the environment and reconnect with their neighbors. Outdated zoning laws, minimum lot sizes, and other counterproductive restrictions can sometimes make the task difficult, but smart local leadership can make all the difference. Perhaps we can once again build our towns and cities for people, not cars.

This "new urbanism" also allows us to focus development around mass transit hubs, often called transit-oriented development. Driving a car emits some three to six times more greenhouse emissions per passenger mile than rail transit. So, despite the inflated promise of ethanol and hybrids, we will not reach an 80 percent reduction as a car-dependent nation.