NEW YORK — This month, the mayor of Mesa, Arizona, a city of about 500,000 inhabitants in the American Southwest, became the 1,000th local leader to sign on to a climate change agreement under the United States Conference of Mayors.

In signing the compact — initiated in 2005 by Greg Nickels, the mayor of Seattle and the president of the conference — local leaders commit to reducing their cities’ carbon emissions in concert with the national goals laid out by the Kyoto Protocol: a 7 percent reduction over 1990 emissions levels by 2012.

As with the country-level signatories to the Kyoto agreement, many cities will fail to meet this goal. But with prospects dimming that world leaders will agree to a substantive successor treaty to the expiring Kyoto accord at the global climate summit meeting in Copenhagen in December, local endeavors like Mr. Nickels’s mayoral agreement would seem to take on a whole new measure of import.

“Locally elected officials can create ripples — and maybe even waves — in the fight against global warming,” Mr. Nickels wrote in the introduction to a report, published this month, highlighting the efforts of 16 mayors in various American cities. “What we do in our cities,” he continued, “whether it’s constructing green buildings, establishing electric car charging stations, planting urban forests or creating legions of good-paying green jobs, can serve as a model for state governments” and for Washington.