In this Tuesday, May 28, 2019 photo a homemade sign is posted on a telephone pole in protest of Central Maine Power's controversial hydropower transmission corridor in Jackman. Credit: Robert F. Bukaty / AP

Mainers will vote Nov. 2 on a referendum aiming to block the Central Maine Power corridor, a 145-mile transmission line project aiming to bring hydropower from Canada to connect with the New England energy grid near Lewiston.

The project, financed by Massachusetts, has attracted controversy along with more than $60 million in political spending from energy companies on both sides of the issue. They have flooded the airwaves with ads that often contradict each other and both sides have accused their opponents of lying about the corridor’s true impact.

To help voters make an informed choice on the upcoming referendum, the Bangor Daily News asked readers what information they felt they still needed to decide how to vote ahead of a virtual forum on Wednesday.

Here are the answers to some of your most common questions.

Who is backing each side financially, and what do they gain from the project’s success or failure?

The financial war over the project is straightforward: It is between competing energy companies that have massive financial stakes in the outcome.

Supporting a yes vote and opposing the corridor are several out-of-state energy companies, led by NextEra, which operates the oil-fired Wyman Power Station in Yarmouth. These companies have spent a combined $16 million. Fossil-fuel companies operating in New England could lose about $1.8 billion over the next 15 years if the corridor project is completed, according to one estimate.

Backing a no vote are CMP and its affiliates, along with Hydro-Quebec, the Canadian energy company that would supply the power. CMP’s parent company, Avangrid, won a contract from Massachusetts to build the corridor, while Hydro-Quebec will sell the hydropower to Massachusetts once the project is complete. They have spent a combined roughly $48 million since the fall of 2019.

What do the retroactive portions of Question 1 mean?

Because the CMP corridor has received certain state approvals, opponents wrote the referendum to include retroactive provisions to ensure it would still apply. If it passes, two-thirds majorities of both legislative chambers would need to approve all transmission line projects since 2014 and certain infrastructure projects on public lands since 2020.

At least for this project, that would be tough sell as a majority of lawmakers have indicated opposition. CMP allies have also identified two other projects that could be subject to the same retroactive review if the referendum passes. However, most business activities in Maine do not involve new transmission lines or public land leases and would not be impacted.

Will the CMP corridor reduce carbon emissions?

Energy analysts say the corridor would reduce net carbon emissions. In the short term, importing Canadian hydropower would reduce the use of gas-fired power plants in New England. Estimates, including one from the Maine Public Utilities Commission, have put the carbon emissions reductions at between 3 and 3.6 million metric tons per year — equivalent to taking roughly 700,000 cars off the road.

There are tradeoffs associated with clear-cutting swaths of forest in western Maine. While emissions reductions associated with reduced natural gas consumption are greater than the amount of carbon absorbed by the trees, some environmentalists still oppose the project. There are also other potential negative environmental impacts, such as habitat fragmentation, that are not directly linked to climate change.

Opponents of the project also contend that hydropower is not as environmentally friendly as wind or solar. That is generally true, although energy analysts say the emissions from hydropower are less than the fossil fuels that the project will replace in the short term.

Emissions associated with hydropower are largely linked to the building of dams, as the vegetation flooded to create the dam slowly releases gases as it rots. The locations and ages of dams affect the emissions they produce, and anti-corridor advocates have pointed to research suggesting a handful of Hydro-Quebec’s dams are worse than average. But the company says its dams are overbuilt right now and it would not need new ones to export power.

As demand for energy increases, Hydro-Quebec’s economic incentives could drive it to invest in sources of power other than dams. The company’s last major hydropower project began more than decade ago, and in recent years, other renewables such as wind and solar have proven to be cheaper in Canada than building more hydropower.

How does sending electricity to Massachusetts affect Maine?

The hydropower generated in Quebec and conveyed via the corridor will be sold to Massachusettts. To compensate Maine for its participation, CMP and its allies agreed to $190 million in rate relief, but that is spread out over 40 years, which, as corridor opponents have noted, only comes out to a few cents per household per month. The energy company is also offering subsidies for broadband, heat pumps and electric cars.

However, Massachusetts’ increased use of Canadian hydropower affects Maine. The two states are on the same grid and currently rely on many of the same energy sources. If Massachusetts uses more hydropower, it will use less of other types of energy. Corridor proponents say this could result in lower prices for Maine and other New England states.