Mainers are already paying the price for the world’s slow response to manmade climate change. Studies like the National Climate Assessment report last month make it clear that we are running out of time if we hope to hold off widespread catastrophe.

That makes climate impact the most important question for regulators who are considering any infrastructure proposal. Will it add to the greenhouse gases that trap heat in the atmosphere? Will it reduce the level of emissions, postponing or even preventing a disaster?

That’s the lens we hope the Maine Public Utilities Commission will use to evaluate New England Clean Energy Connect, a 145-mile transmission line proposed for western Maine that would deliver Canadian hydropower to the regional grid. Based on the representations made to us recently by Hydro-Quebec, this project has the right answer to both questions. With this line, the company would be able to sell as much carbon-free power into New England as could be produced by two nuclear power-plants.

Hydro-Quebec is expanding its capacity, with a new dam coming online in 2020. But even with existing capacity, the company has “spilled” enough water — or released it without generating any power — to produce 10.4 trillion watts of electricity. To put that in perspective, the company is wasting as much electricity as Maine consumes during a year.

There is nothing simple about a project like this. Even though the transmission line is in Maine, the power has been purchased by the state of Massachusetts to meet its ambitious clean power goals. Massachusetts ratepayers will foot the entire cost of the project that never touches their state.

The 145-mile transmission line would be within a 300-foot corridor that would be visible in some scenic vistas. The project will create construction jobs, and it will be subject to local property taxes because it’s on private land.

The line would be built by Avangrid, the parent company of Central Maine Power. They say that it will put downward pressure on Maine electricity prices by creating competition during times of peak demand when natural gas prices spike.

The issue, in all of its complexity, is under consideration by the Maine Public Utilities Committee, with input from the state’s Public Advocate’s Office, which represents the interests of ratepayers.

The project has a number of opponents, including people who live near the corridor, regional power producers and some environmental groups, most notably the Natural Resources Council of Maine, which has accused Hydro-Quebec of “greenwashing.”

The organization alleges that Hydro-Quebec could ship the power purchased by Massachusetts to New England over the new transmission line but make less-clean power available elsewhere, meaning that there would be no net benefit to total greenhouse-gas emissions if those customers filled the gap with fossil fuels.

But Hydro-Quebec’s representatives were very clear: They are currently wasting enough water to fill the Massachusetts contract right now, and their generation capacity is growing. If they are able to make the same representations to the PUC as part of Avangrid’s case, they should put the question of climate impact to rest.

Climate may not be the only issue in this case, but it is the most important. The PUC should give it the weight it demands.