VATICAN CITY — One city banned Styrofoam. Another has the highest percentage of “clean” cars in Europe. Still another has cut greenhouse gas emissions by 29 percent since 1990 — while its GDP grew 19 percent.

Dozens of environmentally friendly mayors from around the world are meeting at the Vatican today to bask in the star power of eco-Pope Francis and commit to reducing global warming and helping the urban poor deal with its effects.

It’s the latest — and perhaps most important — Vatican initiative to keep the momentum alive after Francis released his landmark environment encyclical and as governments head into crucial climate negotiations in Paris in December.

Already, the Vatican has engaged Nobel science laureates, global faith leaders, the U.N. leadership, eco-friendly businesses and even the self-described “secular Jewish feminist” and environmental advocate Naomi Klein to promote Francis’ message that caring for the Earth — and humanity — is an urgent moral imperative.

Now, the pope is turning to mayors, some 60 of whom signed up to attend the two-day meeting at the Vatican. Several belong to the new Carbon Neutral Cities Alliance, whose members have committed to reducing greenhouse gas emissions by at least 80 percent by 2050 or sooner.

Attending is Gov. Jerry Brown of California, which has enacted the toughest greenhouse gas emissions standards in North America, as well as the mayors of New York City, Boston, Oslo, Vancouver and Boulder, Co.

Also represented is San Francisco, which has banned plastic bags and Styrofoam; Stockholm, which has the highest percentage of clean vehicles in Europe; and Berlin, which cut its emissions by 29 percent in the past 25 years.