The big city fix for climate change

FORTUNE -- Jay Carson is CEO of the newly formed C40 Clinton Climate Initiative, which combines previous efforts led by former President Clinton and New York Mayor Michael Bloomberg to leverage big cities in the fight against global warming. He'll have a budget this year of $12 million and a staff of 65.

Carson is only 34 but he's been in the spotlight basically since he graduated from Columbia -- as deputy mayor of Los Angeles, press secretary for former Senate Majority Leader Tom Daschle and for two failed Democratic presidential contenders (John Dean, Hillary Clinton), and communications director for the Clinton Foundation, a job he once described to The New York Observer as "playing cards, riding in cars, traveling the world with President Clinton."

He'll be doing a lot of traveling in this job, too. Fortune caught up with Carson by phone earlier this week while he was waiting at LAX to board a flight back East.

Why do you think cities should lead the environmental movement?

In a number of policy areas, cities are the future. But on this issue in particular it's because elsewhere the hurdles are so high. It is very hard to target one piece of climate action for the entirety of China. Or one piece of climate action for the entirety of the United States of America, if only because the needs in Montana are very different than the needs of New York. This is the genius of C40 and CCI -- you don't need to get Montana. Cities comprise 2% of the geography of the world and 70% of the world's emissions.

Is it also because cities are more agile and can act more quickly and more effectively than nations can?

As Mayor Bloomberg likes to say, while nations talk, cities act. That's the fundamental principle of our organization. [Los Angeles] Mayor Villaraigosa was the genius behind this. He said I can get four or five of my mayoral colleagues and we're 100 million people. I love Montana, but instead of trying to get Montana, let's get a few like-minded mayors around the world on board to really take action. And then bring that action to scale with other similar cities. What worked in Moscow may not work in Los Angeles, but sometimes in surprising ways the policies are transferable.

Another way to look at this is that it's bottom-up instead of top-down. Cities know what the carbon drivers are. I don't want to oversimplify but it's transportation, it's your cars; it's your building output; and it's the generation of your electricity. Those are the three things. So if we work to reduce the carbon output in those areas, we will reduce our overall carbon output.

The way that Mayor Bloomberg and the City of New York did it was they simultaneously set a 30% carbon reduction goal while figuring out over 200 ways that they were going to get it done. That's just the way cities and mayors work. At these international treaty talks, everyone talks about carbon percentage reduction without talking about how that will happen, except in the most macro ways. Cities and mayors don't get to sit around and talk lofty rhetoric and not back it up.

Some Fortune readers might say that what you're describing -- leverage, impatience with rhetoric, a focus on results -- fits business better than it does politics at any level, even cities.

Businesses tend to look at what works, at what will affect the bottom line. And by the way, smart companies around the world see that reducing their carbon emissions actually helps their bottom line. There's this great nexus at Wal-Mart between shrinking its packaging and saving money in terms of transport costs. Fewer trucks on the road, less paper used in packaging, more money saved for Wal-Mart (WMT, Fortune 500). Everybody wins.

Just like a business, a city can't implement a policy that ultimately doesn't work. Green building codes, for example. You cannot pass green building codes that ultimately bankrupt your developers because cities need developers. You have to make sure that your building codes save energy to a degree that, while it may cost slightly more to build, the savings over the long run will benefit developers and building owners.

What kind of green policy initiatives can we expect from cities?

Nothing about this is overly prescriptive. Cities can figure out what works for them. You can literally do this on an XY matrix. One axis is carbon output, ranked 1 to 10. The other, areas of control that the mayor has, ranked 1 to 10. If you get something that's a 10 on both, that needs to be a policy that you're pushing.

In New York, buildings are huge on the carbon output axis. And the mayor has a reasonable amount of control over building codes. Taxis have a huge carbon output and a reasonable amount of control by the mayor. So you go after those two, which Mayor Bloomberg has done. With a far-reaching green building code, which by the way was supported by the Real Estate Board of New York when they understood what the financial savings would be. And you have a green taxi law, which was to some extent fought by the taxi lobby but I think has been embraced by the city; people are coming around. New York has more than 12,000 taxis. Move all those to hybrids and you make a huge impact.

On the other hand, New York has nothing to do with Con Edison (ED, Fortune 500). So New York cannot touch power generation. But the city of Los Angeles -- and by the way, the city of Austin, too, and several other cities around the world -- controls power generation. The mayor appoints five members to the board of the Los Angeles Department of Water & Power, and they run it. So when Mayor Villaraigosa came in, he said, "We need to generate cleaner power, we're far too reliant on coal, let's move more heavily into renewables." He was a visionary in that realm.

What we will do in C40 is link other cities together with municipal utilities and have them learn from Los Angeles. And by the way, L.A. is now implementing a drastic carbon reduction program that is highly affordable and supported by the business community.

Bloomberg's a big-city mayor. Clinton grew up in Arkansas. I'm wondering how they get along.

They both have enormous drive. They both love what they're doing. They both are self-made. These are two guys who started essentially at the bottom rung. One went on to become the first two-term Democratic president since FDR, with the strongest economy that the country has ever seen. The other built one of the most successful companies ever and became a three-term, extremely successful Mayor of New York. That is a bond that they absolutely share. In addition to loving New York.

Interview edited for clarity.