ROCKLAND, Maine — Natural gas should not be part of the country’s clean energy future because its impact on the environment has been significantly understated, a group of local and state activists said Wednesday.

This assertion, made Wednesday at a news conference in Rockland, was timed with the release of the report “Natural Gas and Global Warming.” The report was developed by Frontier Group, Toxics Action Center, and Environment America.

Rockland was where one of several such news conferences were held Wednesday across New England by Toxics Action because of the City Council’s approval earlier this month of ordinances that regulate power plants including natural gas ones. The city approved those ordinances and earlier had passed a temporary moratorium in response to a proposed plant.

“Natural gas has been touted as a ‘bridge fuel’ that can help the United States and the world reduce emissions of global warming pollutants during the transition to truly clean sources of energy. The ‘bridge fuel’ argument, however, hinges on a critical assumption: that the climate impacts of natural gas are modest,” the report’s executive summary states.

“In recent years, a number of studies have challenged that assumption, finding that natural gas production, transportation and storage results in major leaks of methane to the atmosphere that erode or nullify the climate benefits of shifting to natural gas. These findings should lead policymakers to reject natural gas as a ‘bridge fuel’ and instead lead them to redouble America’s efforts to repower with truly clean energy from the sun, the wind and other renewable sources of energy,” according to the report.

Andy Jones, a community organizer with Toxics Action, said the organization is calling for a halt to natural gas extraction and the construction of new natural gas lines and facilities.

He said the use of fracking to extract natural gas has major negative impacts on public health and the environment.

Earlier this month the Maine Public Utilities Commission voted to support the extension of a natural gas pipeline that would expand capacity on Spectra’s line running from eastern Pennsylvania to Massachusetts, where it connects with the Maritimes & Northeast Pipeline, which passes through Maine to Canada. Electricity customers would help pay for the extension under the PUC plan.

Nate Davis, one of the founders of the citizen group Renew Rockland, said he had read the environmental report and agrees with its conclusions. Davis serves on Rockland’s Energy Advisory Committee which helped developed the local power plant regulations.

Davis said that when a natural gas-fired power plant was first proposed in Rockland in early 2015, he initially was “cautiously supportive.” But the more research he undertook, he concluded that the project would not be good for the region’s environment. He said the release of methane during the extraction, transportation and storage of natural gas contributes to rising greenhouse gas emissions.

The ordinances approved by the city do not prohibit a power plant but sets standards to protect the community, he stressed.

“Some of the requirements are truly first in the nation,” Davis said.

One of those first-in-the-nation requirements is that any emissions from the plant must be more than offset from reduced emissions from other companies that receive thermal heating from a power plant. Other requirements include formulation of a decommissioning plan, an aggressive water recycling standard, and a cap on the amount of water used.

Local environmentalist Ron Huber, executive director of Friends of Penobscot Bay, said a natural gas plant would have had negative effects on marine life and would have encouraged sprawl that would be bad for the region. He also said that the use of natural gas, as shown by the study, will increase global air and sea temperatures.

Huber said any additional rise in sea temperatures would harm the lobster industry, similar to what has happened in southern New England.

James Cote of Bernstein Shur Group in Portland responded to an emailed request for comment about the report that was sent to Evan Coleman of Rockland Energy Center, which proposed the natural gas plant Rockland.

“There are no current plans to pursue a project in Rockland,” Cote said.

Cote said Energy Management Inc. of Boston, which was the parent company of Rockland Energy, had no comment concerning the release of the report critical of natural gas.

David Madore from the Maine Department of Environmental Protection said state staff has not yet had time to review the report since they just received it Wednesday.