SAN FRANCISCO — Mayors from around the world yesterday signed an international treaty calling for increased use of public transportation and drastic cuts to the amount of trash sent to landfills.

The signing of the "Urban Environmental Accords" capped the United Nations World Environment Day Conference in San Francisco.

The nonbinding accords list 21 specific actions that can make cities greener.

San Francisco was the first U.S. city to host the annual conference. Much of the conference focused on global warming and what mayors can do to curb emissions of greenhouse gases, such as carbon dioxide, that trap heat in the Earth's atmosphere.

Mayors participating in yesterday's ceremony came from Zurich, Switzerland, Istanbul, Turkey, Melbourne, Australia, Seattle and dozens of other cities.

"What you are doing here today is taking a different approach — a united approach — on the stewardship of the environment," said Rep. Nancy Pelosi, D-Calif., the House minority leader.

By 2030, more than 60 percent of the world's population will live in cities, up from almost half now and just a third in 1950, U.N. Secretary-General Kofi Annan said. Growth poses huge problems ranging from clean water supplies to trash collection.

"Already, one of every three urban dwellers lives in a slum," Annan said in a statement. "Let us create green cities."

The accords call for policies to expand affordable public-transportation coverage for city residents within a decade. They also call for increasing access to safe drinking water, with a goal of access for all by 2015.

Other goals include creating an accessible park or recreation space within a half-mile of every city resident by 2015 and achieving zero growth in the amount of waste being sent to landfills and incinerators by 2040.

Among the most pressing issues was a recommendation to increase the use of renewable energy to meet 10 percent of a city's peak electric load within seven years.

"The challenge is to take these goals and ideas and to manifest them. We are accountable to getting things done," San Francisco Mayor Gavin Newsom said.

Kofi Annan's comments were provided by Reuters.