Coal plants aren't the only power generators coming under scrutiny for their greenhouse gas emissions these days. A new natural-gas-fired power plant in Massachusetts was cleared for construction last week, but only after agreeing to ratchet down its carbon output each year until it goes offline in 2050.

The agreement resolves a legal battle that began in 2012, when the Conservation Law Foundation (CLF) challenged the construction of the Salem Harbor natural gas facility on the basis that it violated Massachusetts' climate policy.

The law in question, the Global Warming Solutions Act, mandates that the state lower its emissions to 25 percent below 1990s levels by 2020 and 80 percent below those levels by 2050. CLF says those goals would be impossible if the plant were to run indefinitely on a business-as-usual basis.

As the first court case to mandate annual emissions reductions at a natural gas plant, the event sets an important benchmark in the United States' transition toward the less carbon-heavy fuel, said Shanna Cleveland, senior attorney with the CLF.

"At this point, when so many people are looking at natural gas as a solution [to climate change], I think this hammers a stake in the ground," she said. "Natural gas is still a fossil fuel, and its unconstrained growth is not consistent with efforts to deal with climate change."

She added, "If [natural gas] infrastructure is going to be built, it will have to be conditioned. There have to be provisions built in to make sure it's only a temporary solution."

Limits of 'low carbon' energy
Around the country, a fleet of new natural gas power plants have swept in on a wave of low prices. Most of them have replaced old, carbon-heavy coal plants, long the bête noire of the climate movement.

For this reason, President Obama and other high-level officials have touted gas as a "bridge fuel" to a low-carbon future dominated by renewable resources. Groups like the CLF urge caution, however, pointing to the possibility of methane leakage and the volatility of gas prices.

And although its carbon footprint at the smokestack may be only 50 to 60 percent that of coal, a gas-fired power plant still puts hundreds of pounds of carbon dioxide into the air every hour, Cleveland said.

"From a national perspective, we have to realize that natural gas is not a climate solution," she said. "It may play a role for a short time and provide benefits by displacing coal plants, but in order to be consistent with climate mandates, there need to be conditions that designate an end to a plant's useful life."

She added, "Gas can't just be a bridge to nowhere."

According to the settlement, which was accepted by the Massachusetts Energy and Environmental Affairs board Thursday, the power plant must lower its carbon footprint by a little more each year and must be offline by Jan. 1, 2050.

By the time it shuts down, the plant must have dropped its emissions by 80 percent relative to its expected start date in 2016.

The plant will have some flexibility in achieving these reductions. It can implement carbon capture technology or purchase carbon credits or offsets from regional suppliers. Massachusetts is party to the Regional Greenhouse Gas Initiative, a cap-and-trade system involving nine states in the Northeast.

"This agreement is forward-thinking as it not only ensures electricity reliability for the region but requires GHG reductions," said Richard Sullivan, chairman of the state Energy Facilities Siting Board. "[Massachusetts] has some of the most ambitious greenhouse gas reduction targets in the nation, and today's decision will help us achieve those targets."

The new gas plant replaces an old coal-and-oil-powered plant located on the edge of Salem Harbor.

Its operator did not immediately return a request for comment.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500