Rep. Seth Berry, D-Bowdoinham.

The Maine House of Representatives has dealt a potentially lethal blow to a study evaluating the purported climate change benefits of the controversial Central Maine Power transmission project.

The House voted 77-66 Tuesday to approve the study, a margin well short of the two-thirds support it needed to pass as an emergency bill.

[What you need to know about the CMP transmission line proposed for Maine]

Democratic Rep. Seth Berry, of Bowdoinham, says the study could conclusively determine if there will be any regional carbon reductions from the 145-mile, $1 billion project that’s designed to help Massachusetts meet it renewable energy goals.

“An answer to that question, Madame Speaker — the most important question — is the least we can do,” Berry said.

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Supporters argue that the study is necessary because there has been no way to determine if HydroQuebec, the electricity supplier, will add hydropower to the region or simply divert existing generation if the project is approved.

Tuesday’s vote makes it less likely that Democratic Gov. Janet Mills, a project supporter who has said the study is unnecessary, will have to veto the proposal.

This article appears through a media partnership with Maine Public.