Four dozen of the world’s largest cities have taken steps to cut 248 million tons of greenhouse-gas emissions by 2020, according to a report issued Tuesday, an announcement aimed at demonstrating that environmental progress can continue in the absence of a broad international climate agreement.

The news, which New York Mayor Michael R. Bloomberg will deliver along with Rio de Janeiro Mayor Eduardo Paes at this week’s Rio+20 Earth Summit, highlights the fractured policymaking landscape that defines environmental issues today. While more than 130 world leaders will try to hammer out a negotiated statement in Rio by week’s end about their sustainable development goals, many of the concrete steps are being taking by community leaders.

“We’re not arguing with each other about emissions targets,” Bloomberg told reporters in a teleconference Monday. “What we’re doing is going out and making progress.”

The C40 Cities Climate Leadership Group — a network of 59 cities, including Los Angeles; Tokyo; Bogota, Colombia; and Addis Ababa, Ethiopia — was launched in 2005 to provide support for mayors hoping to cut greenhouse-gas emissions in urban centers across the globe. The group analyzed data from 48 cities to determine a suite of policies that are now in place to cut 248 million tons of greenhouse gases, the equivalent of taking 44 million passenger vehicles off the road for a year.

The 59 cities of the group, Bloomberg added, have the capacity to cut their carbon output by 1 gigaton, or a billion tons, by 2030 compared with business as usual. That reduction, which could be achieved through steps such as the capture of methane from urban landfills and installation of more-efficient lighting and energy-efficient building codes, would be equivalent to the combined greenhouse-gas emissions of Canada and Mexico.

“This is not only a central government problem,” Paes told reporters, adding that when world leaders gathered in his city two decades ago for the first Rio Earth summit, “it was a nice discussion, we set out some goals, but I don’t think we got much better.”

In addition to the official negotiators walking the halls of the convention center, there are people such as Samson Parashina, president of Kenya’s Maasai Wilderness Conservation Trust. Parashina’s group has worked to protect lions, elephants and key habitat on 280,000 acres of land between Tsavo and Amboseli national parks, by encouraging tourists to observe area wildlife and compensating local residents when wild predators kill their livestock.

In a phone interview, Parashina, a recipient of the U.N. Development Program’s Equator Prize, said grass-roots efforts to generate “alternative economic benefits” for conservation will achieve more than having political leaders declare that certain areas deserve environmental protection. “For us, they need to answer people’s needs in order to have a protected wilderness,” he said.

U.S. officials and others have sought to lower expectations for this week’s U.N. Conference on Sustainable Development, noting that the Rio summit is not aimed at producing a breakthrough agreement on climate change or other high-profile issues. In a telephone news conference Friday, Todd Stern, the U.S. special envoy for climate change and the country’s top negotiator in Rio, told reporters, “Let me also remind you that sustainable development is not at all just about the environment, and this conference is not an environmental conference. This conference is a development conference.”

And former president Bill Clinton said the example of mayors and others will encourage politicians to take action on climate change and other issues in the future.

“The proclamations will come, and the commitments will come, when the proof is there,” Clinton said on the call with Bloomberg and Paes. “I think the power of example is more important than another speech by a political leader.”

But some experts, such as George Mason University environmental science and policy professor Thomas E. Lovejoy, said these disparate efforts to achieve sustainability will not be enough to address the world’s environmental challenges.

“The best one can hope for is a sort of mosaic approach, which by definition won’t be sufficient,” said Lovejoy, who was just awarded the Blue Planet Prize, one of the world’s top environmental honors.