Gov. Charlie Baker still is not on board with the climate policy bill overwhelmingly passed by the Legislature twice in about a month, but this time he has sent it back with proposed amendments he says would make the legislation more palatable.

The bill is designed to push Massachusetts toward net-zero carbon emissions by 2050, establish interim emissions goals, adopt appliance energy efficiency standards, and address needs in environmental justice communities. And while Baker has said he supports those aims, his administration and key lawmakers have not seen eye-to-eye on many of the finer details of the legislation.

"The science is clear -- the Commonwealth, the nation and the world must achieve net zero emissions by 2050 if we are to avoid the worst impacts of climate change," Baker wrote to the Legislature. "In 2020, my Administration adopted net zero as a legally binding limit for 2050 emissions ... This legislation enshrines net zero emissions in statute, further binding the Commonwealth to this important goal."

The amendments Baker sent back cover many of the same topics he cited as concerns last month when he vetoed the same bill sent to him in the waning days of the previous legislative session -- the creation of an opt-in municipal stretch energy code, the 2030 greenhouse gas emissions reduction target, and the sector-specific emission reduction sublimits proposed by the Legislature.

But they also show some flexibility around many of the details, continuing negotiations informed by about three weeks of "robust dialogue" between the administration, lawmakers and outside stakeholders, according to a letter to be filed with the governor's proposed changes.

"I think we have worked very hard with the Legislature over the last three weeks or so to have these discussions, to get into the weeds of policy and data, and to find areas of common ground," Energy and Environmental Affairs Secretary Kathleen Theoharides told the News Service on Sunday. "So we're really grateful to have had that opportunity and I know the governor looks forward to signing this legislation as amended and then getting back to work on all the other climate issues we have to address this session."

The governor returning the climate bill with amendments paves the way for a back-and-forth similar to the process lawmakers and the governor engaged in around recent abortion access and policing reform laws. It is most likely to end with lawmakers either agreeing to some of the changes Baker has suggested and him signing the bill or rejecting his proposed changes and overriding another gubernatorial veto.

On the 2030 emissions reduction target, the governor proposes that the executive branch be allowed to set a range of between a 45 percent reduction from 1990 emissions levels (his administration's preferred target) and 50 percent (which lawmakers wrote into the bill). For the 2040 target, Baker similarly proposes that the executive be allowed to set it between 65 percent and 75 percent.

The administration had previously said the difference between 45 percent and 50 percent could be as much as $6 billion in extra costs to the state and residents, but Baker said in his letter that the flexibility "will also help the Commonwealth avoid the costs that are expected to result from imposing a higher limit, particularly on those who can least afford it."

At least on the issue of the 2030 target, Sen. Michael Barrett, one of the chief sponsors of the climate bill, has suggested that the Legislature might be willing to negotiate and compromise with the governor's team.

"In any event though, we have 2021 and if there's a little disagreement on where we should get to by 2030 in anything that should come out of the Legislature, it is up for further discussion in 2021 and subject to compromise if that's where we need to go," Barrett said on Dec. 31.

Another provision of the bill that Baker previously flagged as an issue but said he is willing to engage on is the requirement that the Department of Energy Resources "develop and adopt, as an appendix to the state building code, in consultation with the board of building regulations and standards, a municipal opt-in specialized stretch energy code that includes, but is not limited to, a definition of net-zero building."

Some in the commercial real estate industry feared that sentence could give cities and towns the authority to ban natural gas hookups for newly-constructed buildings and require that they meet a net-zero emissions threshold. Theoharides said Sunday that the amendments should provide some clarity around how the code would focus things like having a tight building envelope "without necessarily doing some of the things folks were worried about with a net zero code, which might include prescribing solar panels on all buildings or requiring buildings not be connected to gas."

"The Interim Clean Energy and Climate Plan for 2030 (CECP) calls for a high-performance stretch energy code to be available for municipal opt-in by 2022, and allows six years for full adoption statewide by 2028. The amendments I am proposing align with our CECP, provide clarity to industry and municipalities as to how this code will be developed and adopted, and limit cost pressures on new affordable housing," the governor wrote.

He said his amendments would "clarify" that the existing stretch energy code will be shifted under the control of DOER as a "specialized stretch energy code" and that DOER will promulgate an "updated stretch energy code that includes a municipal option for high-performing, energy-efficient new construction that supports our emissions reduction goals" after a regulatory process with "significant" stakeholder input.

When he vetoed an identical bill last month, Baker's veto letter included a somewhat vague paragraph that seemed to reject the Legislature's prescribed offshore wind procurements in favor of the flexibility to contract for clean energy from various sources through a multi-state effort that's still in the early stages of development.

In his amendment letter Sunday, Baker said he is on board with the Legislature's requirement that the executive branch direct Massachusetts utilities to buy an additional 2,400 megawatts of offshore wind power and looks forward to "working with the Legislature on opportunities to regionally procure additional offshore wind and other clean energy resources during this session."

Theoharides said the administration fully supports the procurements called for in the bill and, after talking the issue over with lawmakers, looks forward to developing a regional opportunity to procure clean energy during the new two-year legislative session.

"Ideally, we will be looking at all of this in a regional context in the future, but I think we have the opportunity to work on that this session as conversations continue with neighboring states about reforming the regional markets and ensuring that we can work together as a region to build out the transmission and interconnection we need to support clean generation throughout the region," the secretary said. "So we absolutely need additional authorization to procure clean power regionally and that will be a focus for us this session."

If the Legislature rejects Baker's amendments and the governor ends up vetoing the bill again, the House and Senate both appear to have the votes needed to clear the two-thirds threshold required for an override. The House passed the bill on a 144-14 vote and the Senate passed it on a voice vote, meaning individual senators' positions were not recorded, though the bill passed last session with 38 senators in support and there are only two new senators who did not cast votes last year.