Mayors and regional leaders from around the world welcomed Pope Francis’s arrival in New York on Thursday by signing a pledge to drastically cut carbon pollution, joining a growing movement of local jurisdictions that are pushing for aggressive action on climate change regardless of what national governments choose to do.

The officials, representing cities and provinces from San Francisco to Kathmandu, Nepal, stood in line to sign what organizers called the “Under 2 MOU,” a voluntary pact that seeks to reduce emission of greenhouse gases by at least 80 percent compared with 1990s levels.

Participants said they hoped to spur world leaders into agreeing to a strong global treaty in Paris later this year, but they weren’t waiting to see whether others would follow their lead.

“We, at our order of government, can do things without the complexity of treaties,” said Glen Murray, Ontario’s environment minister, who joined counterparts from five continents in a ceremony that coincided with the pope’s arrival in New York. “By making cooperative commitments and supporting one another, we are already doing what many national governments are failing to do.”

The additions Thursday brought to nearly 40 the number of major cities and provinces to sign the extraordinarily ambitious — though nonbinding — pact. Signers commit to either cutting pollution to 80 to 95 percent below 1990 levels, or attaining a per capita emissions goal of two metric tons of carbon emissions by 2050. The current per capita average of U.S. citizens is about 18 tons.

“We’re just getting warmed up,” said California Gov. Jerry Brown (D), who helped launch the movement. “And I promise you, no opposition . . . will stop California from reaching the sustainable goals we commit to tonight.”

Brown’s office said the signers — who include representatives from New York and Mexico City — collectively represent 313 million people and more than $8.7 trillion in gross domestic product. If they were a single country, it “would be the third largest economy in the world, behind only China and the United States,” the governor’s office said in a statement.

The Under 2 MOU movement is one of several recent initiatives by “sub-national” governments and business organizations that are seeking to take the lead in battling climate change. Jeffrey Sachs, the director of Columbia University’s Earth Institute and an adviser to the United Nations on climate change, referred to what the localities were doing as “deep de-carbonization.”

“California is the most important economy in the world doing it at scale,” he said. Under the Brown administration, California generates one-quarter of its electricity from renewable energy, and Brown has set a goal of 50 percent renewables by 2030.

Brown said agreements such as the MOU, while voluntary, were needed in order to “make sure the world takes the turn.”

“It’s easy to say ‘de-carbonize,’ but to actually carry it out takes political will,” he said.

The announcements by the mayors and governors came as a number of prominent corporations pledged expanded efforts to reduce their own carbon emissions. More than 60 companies, including several of the world’s largest, have committed to pollution cuts of up to 50 percent over the next decade in an effort coordinated by the U.N. Global Compact, a United Nations-led business initiative.

“Climate plays a significant role in the long-term viability of our business,” said Catherine Gunsbury, director of sustainability and transparency at General Mills, which pledged a 28 percent cut in greenhouse gas emissions of the company’s worldwide network by 2025. “We recognize that we must do our part to protect and conserve natural resources. Our business depends on it, and so does the planet.”

Among dozens of other companies making similar pledges were Coca-Cola, Pepsi, Target, Colgate-Palmolive and Procter & Gamble.

Earlier in the day, Brown joined a panel of environmental officials and scientists in calling for action against a class of pollutants blamed for accelerating the rate of global warming. Among the short-lived climate pollutants are several industrial coolants that act as powerful greenhouse gases when released into the atmosphere.

International negotiations are underway on a treaty to scale back production of hydrofluorocarbons, or HFCs, a chemical widely used in refrigerators and air conditioners. The United States and the European Union have already taken steps to phase out the chemicals in favor of more environmentally friendly compounds.