A New Jersey-based energy developer this week secured the legal breathing room it needs to build one of the largest power plants in Massachusetts. All it took was a commitment to run the plant at a fraction of its capacity, to close it for good after 35 years, and to try to impose similar restrictions on any other developer who wants to open up a new power plant in Massachusetts.

The energy developer, Footprint Power, struck a settlement with the Conservation Law Foundation this week. The settlement will end CLF’s attempts to overturn permits allowing Footprint to build a gas-fired power plant in Salem, and likely clears Footprint to begin construction on the plant, which would open in mid-2016. The plant could become one of New England’s largest sources of air pollutants when it opens, but its emissions would plummet over its lifespan. The CLF believes that allowing the construction of a new, legally handcuffed power plant puts a new set of teeth into the state’s ambitious global warming laws, and puts prospective redevelopers of sputtering coal plants in Somerset and Holyoke on notice.

Footprint Power snapped up the aging Salem Harbor coal power plant in 2012, and proposed redeveloping the coal plant as a gas-fired facility. Salem Harbor’s previous owner, Dominion, had decided to shut down the money-losing coal plant rather than invest in pollution-control technology that would appease the plant’s environmental opponents.

In seeking to repower the Salem site with natural gas, Footprint figured that it had both the energy markets and environmental trends working in its favor. A boom in domestic natural gas production has tilted the region’s power market strongly in the favor of power plants that run on gas, and since gas plants run about twice as cleanly as coal plants, the rise of gas power has brought on a sharp drop in greenhouse gas emissions in Massachusetts. But Footprint’s Salem plant ran into static from the CLF and other environmental advocates, who argued that plugging a large new gas power plant into a market already overrun by gas plants would do little to bring down greenhouse gas emissions.

The CLF has noted that the state has already passed the point where new gas plants would automatically lead to lower carbon dioxide emissions, because cheap natural gas has already sidelined coal power. Instead, the environmental group has argued that building new gas plants would only lock in the status quo at a time when the state’s Global Warming Solutions Act has mandated aggressive reductions in carbon emissions — cutting emissions by 80 percent by the year 2050.

“There will be some amount of coal to gas conversion, but just switching isn’t enough,” argues Shanna Cleveland, the CLF staff attorney who sued the state to overturn Footprint’s Salem permits. “We can’t simply switch [fuels] and get to where we need to be.”

The CLF lawsuit against Footprint’s Salem power plant hinged on the argument that Massachusetts couldn’t hit its 2050 emissions target while also adding another gas plant to a state that already draws two-thirds of its electricity from gas plants. The settlement the two sides reached this week allows Footprint to open its Salem gas plant, but institutes a sliding emissions cap that puts Footprint’s power plant on a trajectory that lines up with the state’s 2050 emissions targets. Footprint officials could not be reached for comment.

The settlement allows Footprint to construct one of the largest gas-fired power plants in Massachusetts but, after 10 years of operation, subjects the plant to a series of increasingly tight emissions caps. The caps would cut carbon dioxide emissions at the plant by 77 percent between 2025 and 2049. Footprint has committed to shutting down the plant altogether in 2050. The CLF believes this is the first time an energy developer in the region has agreed to put a mandatory retirement date on a newly constructed power plant.

There are some allowances for emissions overages at the Salem facility. Footprint could make up for exceeding its emissions cap by investing in renewable energy and efficiency projects, or by purchasing carbon allowances in the regional cap-and-trade market at a steep premium. But, as the cap tightens, the only realistic way for Footprint to comply is by running the plant less often. And as the plant runs less often, Cleveland argues, it will put more pressure on renewable energy developers to step up their own production.

“It’s really important that if gas really is a bridge fuel, we know where it’s taking us, and we know that there’s an off-ramp,” Cleveland argues. “We didn’t want to face the situation we faced three years ago in Salem, where we had a coal-fired plant that was uneconomic, but we couldn’t get it off the system.”

Cleveland says the state’s strict 2050 emissions target all but mandates “a decarbonized electric sector,” where coal and gas plants alike yield to renewables, super-efficient buildings, and advanced energy storage systems. However, the law that created the 2050 emissions target doesn’t have many enforcement mechanisms. Cleveland believes that cuffing Footprint’s gas plant to an aggressive emissions cap helps put teeth into the state’s 2050 target. And since the Footprint settlement commits the CLF to seeking similar concessions from any other new power plant developer in the state, the CLF will use its settlement with Footprint as a blueprint for dealing with developers who might look to repower sputtering or shuttered coal plants, like the ones in Somerset and Holyoke.