Massachusetts on Tuesday joined a coalition of eight Northeast and mid-Atlantic states that will work over the next year to try to develop a market-based system to reduce carbon emissions from the transportation sector, which accounts for nearly half of all emissions in the state.

The project, which will be modeled on the 10-year-old Regional Greenhouse Gas Initiative used to cut carbon emissions from power plants, has the potential to become a major piece of the state's efforts to fight global climate change.

Energy and Environmental Affairs Secretary Matthew Beaton said Tuesday that the economics at stake make a regional approach essential to tackling the issue of carbon pollution from transportation. At least one leading legislator worries, however, that Massachusetts may be putting a cap on its own ambitions to lead the way in reducing emissions and meet the increasingly challenging goal of limiting the impacts of climate change.

Gov. Charlie Baker announced Tuesday that Massachusetts had signed on to an agreement with eight states and the District of Columbia to develop a framework in 2019 to reduce transportation sector emissions. The partnership was born out of the Transportation Climate Initiative overseen by the Georgetown Climate Center.

Other participating states include Connecticut, Delaware, Maryland, New Jersey, Pennsylvania, Rhode Island, Vermont and Virginia. Some TCI member states elected not to take part, including New York where just days earlier Gov. Andrew Cuomo set a goal of carbon-neutral electricity in his state by 2040.

While the parameters of the program must still be developed, officials said it is likely to take the form of a cap-and-invest program similar to RGGI, where gasoline distributors would purchase credits in order to exceed a cap that would be brought down over time. The money raised would be invested back into state-level climate change programs.

The level at which the initial cap is set, as well as the point of regulation, figure to be sticky negotiating points between the states, but officials familiar with early talks suggested there was little appetite to impose fees at the consumer level.

The formation of the multi-state group came on the same day environmental scientists and activists warned lawmakers that the state needed to get more aggressive to address the potential impacts of climate change.

"The big elephant in the room right now is transportation, and our buildings," Beaton said.

Transportation is responsible for 44 percent of all emissions in Massachusetts, and buildings are responsible for another 39 percent.

"I feel comfortable having this conversation on a regional basis given the potential for economic impacts if done alone by a state," Beaton told the House and Senate Committee on Global Warming and Climate Change.

Sen. Michael Barrett, however, said he had "misgivings" about the approach given that Massachusetts is already ahead of a lot of the states in the coalition in terms of reducing overall emissions.

"That puts the slowest moving state in the coalition in the driver's seat," Barrett said.

The Lexington Democrat also said that he's worried about potentially wasting an entire year waiting to see what the group produces that could otherwise be spent developing a Massachusetts-centric strategy to speed up emission reductions.

"I'm taken aback a little bit," Barrett told the News Service. "The governors are asking for a one-year timeout on pressure from those of us concerned about climate change. That is an ambitious ask. I do worry that an effort like this, which involves so many states and so many moving parts, is both a potentially important breakthrough and a great political dodge."

Beaton announced Tuesday that through 2016 Massachusetts had reduced carbon emissions by 21.4 percent below 1990 levels, and was on track to achieve the requirement of 25 percent reduction by 2020.

That good news, however, was overshadowed by testimony from scientists from Woods Hole, UMass Boston, and the Union of Concerned Scientists that told lawmakers that the requirement in the Global Warming Solutions Act of an 80 percent reduction in emissions below 1990 levels by 2050 is no longer adequate.

The scientific community, according to those experts, now believes that it will be necessary to achieve net zero emissions by 2050 to keep global warming to 1.5 degrees Celsius this century and avoid some of the more devastating impacts of climate change.

Those assessments, they said, are based on the recently released United Nations Intergovernmental Panel on Climate Change report in October and the National Climate Assessment report in November.

"In short, the situation is dire and its getting worse," said Susan Natali, of the Woods Hole Research Center.

Meeting that "net zero" target, the experts said, will require reductions from all sectors, including transportation, electricity and buildings, as well as removing carbon from the atmosphere.

"We need to be able to walk and chew gum and maybe juggle all at the same time," said David Ismay, staff attorney at the Conservation Law Foundation.

Sen. Marc Pacheco, who convened the oversight hearing, said he hoped to come to "some type of New Year's resolution" to take action in 2019, and not wait until the second half of the two-year session to act. He seemed particularly interested in updating the requirements of the GWSA to speed up the pace of the state's emission reductions to meet the new 2050 recommendations.

"The number needs to change for us to do right by humanity. The planet will take care of itself. The planet will be just fine. I'm just worried about all the species living on the planet," Pacheco said.

Natali said there is "robust and clear science" that global warming has contributed to more frequent and dangerous hurricanes and wildfires, and John Rogers, of the Union of Concerned Scientists, said warmer temperatures will lead to public health risks from worsening air quality and an increased prevalence of infectious diseases like West Nile Virus.

"That's a disease we've become familiar with in Massachusetts. It's going to get a lot worse," Rogers said.

Ismay urged the House and Senate legislators at the hearing to upgrade the state's emission reduction requirements to "net zero emissions by 2050," and ramp up interim targets for 2030 and 2040 so as not to fall too far behind. He also encouraged the development of a "portfolio of regulations" to set annual targets that can be measured to replace oil furnaces and heavy vehicle fleets.

Barrett said it was important that the legislators not get bogged down in a debate with the administration about the current 2020 goal, whether the state winds up hitting the goal or just missing it.

"We need much more aggressive overall goal setting," Barrett said.

Beaton told the committees that the administration was getting ready to put out a request for proposals to do a study on the current 2050 emission reduction requirements and help the state identify "realistic pathways to do it in a cost-effective manner."

Pacheco asked the administration to take a fresh look at the emission reduction efforts underway in light of the new science that suggests the state may need to get more aggressive.

Related to transportation, Pacheco said the shift toward electric vehicles will require even greater electric capacity, meaning the importation of large scale hydro and off-shore wind energy development will be critical.

Pacheco said the Legislature has authorized 3.2 gigawatts of off-shore wind, but should consider upping that to 5 gigawatts or more.

"We also need hydro to make this all work, especially given the numbers now that we need to achieve. We will not get there without significantly more wind and backup with storage with hydro," Pacheco said.

Beaton told lawmakers, "I think we're still in a good place," when asked about the status of the Central Maine Power transmission line project that is supposed to bring hydro-power from Quebec into Massachusetts, but acknowledged that the transition to a new Democratic governor in Maine is ongoing.

"We haven't hit a panic button there by any means," Beaton said, detailing some mitigation efforts Central Maine has undertaken to address environmental concerns with the project.

Transportation and environmental advocates reacted mostly positively to the Transportation Climate Initiative's pursuit of a carbon-pricing program.

Transportation for Massachusetts Director Chris Dempsey said RGGI was a good model to replicate to address transportation sector emissions, while Cindy Luppi, coordinator of the Massachusetts Campaign for a Clean Energy Future, called the multi-state project "a strong step forward."

"Scientists are urging us to act boldly and quickly to address the accelerating pace of climate change, and this policy could help us do that," Luppi said.