The state remains on course to meet its legal obligations to reduce greenhouse gas emissions by a quarter below 1990 levels by the end of the decade, according to a report released Tuesday by state officials.
A significant portion of those cuts, however, rely on the Legislature passing a bill that would compel utilities to sign long-term contracts to buy hydroelectric power from Canada or other renewable energy from outside Massachusetts.
"A greenhouse gas emissions reduction of at least 25 percent by 2020 is attainable," said Matthew Beaton, the state's secretary of energy and environmental affairs, in a letter accompanying the report. "Reaching this goal requires consistent effort and collaboration across all sectors."
The administration's report stands in stark contrast to the assessment of environmental advocates, who have challenged the state's numbers and raised questions about whether its hydropower plans are viable.
In the report — the first update of the state's clean energy and climate plan since it was issued in 2010 — officials say the state expects to cut emissions 26.4 percent below 1990 levels by 2020, surpassing their obligations under the 2008 Global Warming Solutions Act.
The plan expects that nearly 17 percent of the required emissions cuts would come from hydropower or other clean energy imports. Another 23 percent would come as the result of policies to increase energy efficiency, while nearly 16 percent would come from new vehicle efficiency standards.
The plan envisions the rest of the cuts coming from a range of other policies, including new building codes, requirements that utilities plug leaks in natural gas pipelines, and incentives to increase the amount of solar and wind energy projects.
"While progress to reduce greenhouse gas emissions has been made on many fronts, the plan update highlights the need for immediate action on our legislation for clean and affordable hydroelectricity and other renewable resources in order to achieve our 2020 goal and position us to meet the long-term reduction targets," Governor Charlie Baker said in a statement.
But environmental advocates have raised doubts that the state will be able to comply with the law.
In fact, lawyers for the Conservation Law Foundation in Boston this month argued before the state's top court that the Baker administration, as well as that of former governor Deval Patrick, violated the law by failing to enact policies that would result in the required emissions reductions. The challenge of making those cuts, they note, will be greater with Pilgrim Nuclear Power Station — the state's largest provider of clean power — set to close as early as next year.
Advocates insist the state has fallen behind and needs a major course correction — not just action on the hydro plan — to meet the law's requirements. They also note that even if lawmakers pass a hydroelectric bill, the expensive power lines might never get built. Some would likely pass through New Hampshire, where the proposal remains highly controversial, and others would require an expensive extension of lines to Vermont.
In 2014, before Pilgrim announced it would close, a collaborative effort by local environmental groups called the Global Warming Solutions Project released a report that projected that Massachusetts would cut its emissions by only 20 percent below 1990 levels. A more recent report by the Conservation Law Foundation, which factors in the closure of Pilgrim, estimates that the state, without any significant policy changes, is more likely to cut its emissions between 16 and 19 percent.
The reliance on hydropower, they add, doesn't appear to take into account that hydropower is not entirely carbon-free energy. It relies on reservoirs that flood forests, decimate trees, and release carbon dioxide.
"A significant portion of the plan relies on unidentified Canadian hydro resources, with unidentified greenhouse gas emissions profiles, based on an assumption that the transmission lines will be permitted, constructed, and operational prior to 2020," said Greg Cunningham, director of the clean energy and climate change program at the Conservation Law Foundation. "All of those assumptions leave the Commonwealth's assertion that it will meet its 2020 goal highly tenuous."
Ken Kimmell, who served as commissioner of the state's Department of Environmental Protection during the Patrick administration, said the state has left little room for error.
"It would be helpful to start developing other policies in case this strategy doesn't pan out, such as a greater commitment to electric vehicles, carbon pricing for transportation and heating, and expanding solar and onshore wind, and developing offshore wind," said Kimmell, who is now president of the Union of Concerned Scientists.
Administration officials acknowledged in an interview that their plan relies on hydropower to meet the emissions targets.
But they noted they're also pressing other initiatives to reduce emissions, such as planting more trees, reducing the use of refrigerants that produce carbon emissions, and investing in developing energy storage, which would make it easier to harness power from solar and wind energy.
And they said they're looking past 2020. The law requires the state to cut its emissions by 80 percent below 1990 levels by 2050. Administration officials noted that they have joined eastern Canadian premieres and New England governors in signing a resolution calling for a 35 to 45 percent cut in greenhouse gases by 2030.
"The Commonwealth has made great progress in addressing climate change, and the plan update lays out many innovative strategies to reach our 2020 goal," Beaton said.
David Abel can be reached at email@example.com. Follow him on Twitter @davabel.