BioEd Online

Representatives of more than 20 world cities have gathered in London to trade ideas on how to address climate change. The summit is the first to bring together city leaders, rather than national governments, to discuss attempts at reducing greenhouse emissions.

"Cities have a very special responsibility," says London's deputy mayor Nicky Gavron, one of the meeting's hosts. "In terms of delivering change on the ground, cities have control of transport, managing waste and future planning," she told news@nature.com.

Cities are also the place where most of the world's people live. This year, the proportion of the world population living in urban areas passed 50% for the first time. And because of their dense transport and power systems, cities account for 75% of the world's energy use.

But cities also have the power to change rapidly through schemes that make big cuts in emissions. Look at London's anti-congestion car toll, says Steve Howard, chief executive of The Climate Group, an international organization that aims to promote joint business and government schemes to fight climate change.

Since the introduction of the London car tariff in 2003, carbon dioxide emissions in the centre of the city have fallen by 19%. "That's why we're looking to the leading cities: the Londons, the New Yorks, the Beijings," says Howard.

Howard hopes that some of the schemes presented at the meeting, called the World Cities Leadership Climate Change Summit, will inspire other cities. As London mayor Ken Livingstone puts it: "The things that work, we will all copy from one another."

Transports of delight

Improved transport is key to reducing cities' greenhouse emissions and one city that is definitely ahead of the pack, says Howard, is Curitiba, in the Brazilian state of Paraná.

Jaime Lerner, an urban planner who lives in Curitiba, told the meeting how his home town's huge buses, each carrying 270 people and running at one-minute intervals, transport the same passenger volume as a New York subway line. Although the buses still emit carbon dioxide, they are far cleaner than the equivalent cars, and the system was quicker and cheaper to create than a train line.

Howard also singles out Mexico City, which next year aims to finish replacing its 80,000 ailing Volkswagen Beetle taxis with lower-emission vehicles. The city has a tangible incentive, he points out: water catchments in the surrounding forests are being dried out by rising temperatures.

Other cities that have led successful initiatives include Toronto, which uses nearby lake water to cool its downtown buildings, and Seattle, the champion greenhouse-gas reducer with a 48% cut from 1990 to 2000. Even lowly Woking, near London, has built a leisure centre powered by a hydrogen fuel cell that emits only water.

Getting the right scale

The problem is scaling up technologies such as fuel cells and solar panels so that they become viable city-wide, Howard says. "At the moment solar power, for example, is too expensive. We need to create markets for these technologies. We see that as a three-way partnership between businesses, and national and regional governments."

As this week's meeting aims to show, it is city governments who have the leverage to make rapid changes with tangible, quick results. This summer, London set up a new Climate Change Agency, which aims to get green projects up and running as soon as possible, even if they need outside funding to make them happen.

One such project will involve the conversion of the entire city's bus fleet to hydrogen power. As London mayor Ken Livingstone pointed out at the meeting, this is too expensive a one-off investment even for a city with London's financial muscle. But if a current trial run proves effective, European policy-makers might be persuaded that such technology should be made standard, and pledge the required funds.