Warning of dire consequences if no action is taken to combat climate change, lawmakers are again making an ambitious push to transition Massachusetts to all-renewable energy sources within two and a half decades.

Legislation unveiled Monday by a group of elected officials and activists outside the House chamber would move the state to 100 percent renewable electricity by 2035 and 100 percent clean power for transportation and heating by 2045. Rep. Sean Garballey, one of the bill's authors, described it as "the most important bill" that could be taken up this year.

"If you live in a coastal community, if you live in a dry, arid community, people's lives are being destroyed and people are being killed today for issues that are directly linked to climate change," said Rep. Marjorie Decker, who filed the bill with Garballey and Sen. Jamie Eldridge. "Climate change is already impacting the way we live."

A major report from the United Nations' Intergovernmental Panel on Climate Change in October carried a grim forecast: Without action to cut carbon emissions significantly in the next three decades, the world will experience rapid ocean acidification, more intense food shortages and frequent extreme weather.

Advocates on Monday cautioned that Massachusetts specifically would be prone to rising sea levels flooding coastal communities and far more frequent days of 90-plus degree heat.

"Our message today is clear: Massachusetts needs to get off dirty, polluting energy as soon as possible," said Ben Hellerstein, state director of Environment Massachusetts.

The bill has support from a range of other environmental groups. Representatives from MASSPIRG and the Sierra Club participated in the press conference Monday, and a letter passed by bill supporters included signatures from groups such as Climate Action Now MA and MassSolar.

In 2017, legislators proposed a similar package to push Massachusetts to all-renewable energy, but the measure never advanced beyond a study. A compromise bill authorizing additional offshore wind development, among other components, passed at the close of the formal session in July.

The latest version is more significant than its predecessor, speeding up the original target date for 100 percent renewable transportation and heating from 2050 to 2045.

"The goal is to be ambitious," Garballey said. "We believe it's an achievable goal. We have a moral obligation to our country and our world."

Supporters are optimistic they can find greater success this time given the urgency of climate change. About 30 co-sponsors have already signed on, compared to just four who had co-sponsored the previous bill at this point in the session, according to Garballey.

Constituents, Decker said, are "organized and galvanized and agonized" in demanding action.

"The number of hurricanes and the impact that's happened, the fires that have happened — it's not just hypothetical and it's not just scientific data," she said. "The fear is real and the anguish is real."

Several communities in Massachusetts, including Cambridge and Lowell, have already made commitments to move to all-renewable energy systems. California and Hawaii are the only states with pledges to end their use of fossil fuels by 2045, according to the Sierra Club.

With the Global Warming Solutions Act of 2008, Massachusetts became one of the first states to set specific targets for greenhouse-gas reductions. But as climate warnings grow, the topic will be a key topic on Beacon Hill this session.

Last week, Sen. Marc Pacheco and Rep. Ruth Balser filed legislation to update the GWSA, calling for net zero carbon emissions by 2050. More than a dozen other bills have been filed to increase access to clean energy sources, invest in modern transit systems and support green programs at the community level.

Republican Gov. Charlie Baker has also cited climate change as a priority during his second term. As part of his fiscal year 2020 budget, Baker proposed increasing real-estate transfer taxes to fund mitigation and adaptation programs.

"The federal government isn't going to step in," Garbarelly said Monday, pointing to frequent denials of climate change from President Donald Trump and many Republicans in Congress. "So Massachusetts needs to be a leader in the world and lead the way for the rest of the country."