The Massachusetts Senate next week plans to take up a far-reaching package of climate bills whose major components include an electric MBTA bus fleet by 2040, carbon-pricing mechanisms for transportation, homes and commercial buildings, and a series of five-year greenhouse gas emissions reduction requirements that ramp up to net-zero emissions in 2050.

The three bills, teed up for debate on Thursday, Jan. 30, with amendments due by Monday, amount to what Senate President Karen Spilka called a "comprehensive plan for the state" to respond to an international issue: global climate change.

"This is a race against time," Spilka told reporters. "Climate change is changing not only Massachusetts and the United States, it is changing the face of our planet, and our planet's survival is at stake."

The carbon pricing and net-zero emissions provisions are both contained in one piece of legislation, dubbed An Act Setting Next-Generation Climate Policy. The other bills address energy efficiency and electric vehicles.

The electric vehicles bill directs the MBTA to limit its bus purchases and leases to zero-emissions vehicles starting in 2030 and operate an entirely zero-emissions passenger bus fleet by Dec. 31, 2040, according to a Senate Ways and Means Committee summary. To address transportation emissions, it also seeks to make permanent an existing rebate program for consumers buying electric vehicles.

Targeting both MBTA buses and individual car purchases is an approach with the goal of "helping people regardless of income to make sure that the air gets greener and the emissions go down," said Sen. Michael Barrett, co-chair of the Telecommunications, Utilities and Energy Committee.

Barrett said he has been working on assembling the package of legislation since June and that its overall goal is for the state "to do its part in keeping global temperatures below 1.5 degrees Celsius above pre-industrial levels," something he characterized as "very hard to do."

"Actually getting there is really going to take everything Massachusetts can muster," he said. "The language in this bill is very no-nonsense about how we're going to get there."

On carbon pricing, the bill takes a similar approach to language the Senate approved in 2018, leaving it up to the governor and executive branch to choose a specific methodology but setting deadlines for its adoption. That measure did not survive talks with the House last session and was dropped from the clean energy bill that ultimately became law.

Barrett, a Lexington Democrat, has been filing bills since 2013 that propose a revenue-neutral carbon fee, with the money generated returned to Massachusetts citizens.

"For several years the bill struggled," Barrett said. "We did not find traction in the House in particular. I want to be respectful of the legislative branches and respectful of the governor. It seemed to me after two or three years that we weren't moving quickly enough. I decided I wanted to put a price on carbon by any path we could lay our hands on, so I backed away from my preferred method."

Giving latitude to the governor rather than spelling out a specific mechanism helped get more senators on board with the idea of carbon pricing last session, Barrett said.

This year's bill allows the governor to choose among a revenue-neutral fee, a revenue-positive tax, or a cap and trade system like the Transportation Climate Initiative Gov. Charlie Baker is pursuing with other states. It would require a carbon-pricing mechanism to be in effect for the transportation sector by Jan. 1, 2022, for commercial, industrial and institutional buildings by Jan. 1, 2025, and residential buildings by Jan. 1, 2030.

Barrett said the 2030 timeframe for residential carbon pricing is to allow time for cleaner home heating alternatives to evolve and for more energy-efficient homes to be built, in hopes of keeping costs down for homeowners.

The bill's cost implications, for consumers, businesses and property owners, were not the focus of a briefing senators held Thursday morning before the bills were introduced during an 11 a.m. Senate session.

The idea of requiring Massachusetts to speed up its carbon emission reduction efforts and hit net-zero status by 2050 got a significant boost on Beacon Hill this week, with Baker, Spilka and House Speaker Robert DeLeo each declaring their support for the concept. Backing from the governor and the leaders of the two legislative houses creates likelihood that some version of a net-zero emissions policy becomes law this session. Energy and Environmental Affairs Secretary Kathleen Theoharides told the News Service Thursday that she plans to issue a letter of determination in the coming weeks to formally establish a policy of achieving net-zero carbon emissions by 2050.

Under the Senate's approach, the secretary of energy and environmental affairs would be required to set the limit of net-zero emissions by 2050, with interim targets every five years, and develop "comprehensive plans" to reach each of those limits. The bill requires that the 2030 limit be at least 50% below 1990 levels, and the 2040 limit at least 75% below 1990 levels.

A 2008 law requires the state to reduce its emissions to 80% below 1990 levels by 2050. Emissions must be 25% lower by 2020, and the most recent data show that Massachusetts emissions in 2017 were down 22.4% from 1990 levels.

Since Baker on Tuesday night announced he was committing the state to net-zero emissions in 2050, some advocates have called for the state to pursue a more aggressive approach.

"Changing our emissions goal from '80% reduction by 2050' to 'net zero by 2050' may make no difference in accelerating the Commonwealth's transition from fossil fuels to clean energy," Ben Hellerstein of Environment Massachusetts said, calling for the state to instead entirely eliminate its use of fossil fuels. "Most of the additional emissions reductions could be met through dubious offsets and accounting changes."

The press release Spilka's office issued on the climate legislation included statements of support from Boston Mayor Martin Walsh, the Massachusetts Sierra Club, Northeast Clean Energy Council, the Environmental League of Massachusetts, Acadia Center and the Mass Climate Action Network.

Other elements featured in the carbon emissions-related bill include:

The establishment of a new Climate Policy Commission, which Barrett said would serve as an independent watchdog over government's response to climate change.

The creation of a mission statement for the Department of Public Utilities, requiring it to prioritize safety, security, reliability of service, affordability, and emissions reductions.

Development of a net-zero energy code that municipalities could opt into if they choose to move away from fossil fuels as a heating source.

Increased membership on the Board of Building Regulation and Standards, including new seats for experts in energy efficiency.

A requirement that solar energy incentive programs set aside a portion of future allocations for low-income neighborhoods.

Barrett said climate change has moved so quickly that state agencies have not had a chance to catch up.

"The Legislature has to see to it that all the resources of the executive branch are mustered together to reach net-zero by 2050, because this is a heck of a challenge for us, and we can't do it unless everyone has a laser focus and becomes serious about the job rather soon," he said.