Mayor Martin Walsh on Tuesday released an update to Boston’s Climate Action Plan, which he says will accelerate efforts towards carbon neutrality. The move is specifically aimed at cutting carbon emissions from Boston’s buildings, the single greatest source of emissions citywide.  

“Climate change is the defining challenge of our time,” Walsh said. “As a coastal city, Boston is at the frontlines of this global crisis, and we understand the urgency. While national action is at a standstill, cities like Boston are leading with plans, solutions and results.

He added: “The 2019 update to our Climate Action Plan is our roadmap to carbon neutrality, and together we will ensure all of Boston’s residents will benefit from our work to protect against climate change, and create an equitable, resilient city for all.”

The update sets Boston’s priorities on carbon neutrality for the next five years, with the ultimate goal of making Boston carbon neutral by 2050. 

With Boston’s buildings accounting for roughly 70 percent of citywide emissions, the city will be targeting the largest buildings. Going forward, the city likely will consider fining organizations that don’t retrofit their buildings, probably through an alternative compliance payment. 

“The plan really comes down to two things when you think of the existing building stock and the ity’s capital plans,” said Pat Brophy, the City’s Chief of Operations. “We want to get to net zero buildings and if we can’t achieve that for some reason we want to be designing buildings for the next generation of Bostonians.”  

Steps outlined in the Climate Action Plan include the development of new zoning requirements for a zero net carbon new construction in large projects — 35,000 square feet or greater— and guidelines for zero net-carbon city-funded affordable housing.

“I think most people in the real estate and development community want to help the city on its path to carbon neutrality,” said Christopher Cook, who heads the city’s environment commission. “But there will certainly be instances where we have to move people in the right direction.” 

Renew Boston Trust is a program that looks at ways to retrofit existing municipal buildings. The Trust borrows money against future savings to fund the work that will result in more energy efficient buildings.

“Through the last several capital plans that the mayor has announced, we’ve funded $45 million into the programs that come out of the Renew Boston Trust,” said city CFO Emme Handy. “We expect that phase one of the program will be completed with about $10 million worth of work sometime in the spring.” 

The city had already planned for retrofitting jobs in 20 municipal buildings over the course of the fall and spring, and is actively planning phase two, which will allocate the remaining $35 million that will come from the FY20 capital budget. 

“New municipal buildings will be net zero carbon, and we will have energy performance standards for the private sector,” Cook said. “We envision that it will take us anywhere from a year to 18 months to develop those standards.”

Walsh was scheduled to fly to Copenhagen on Tuesday to attend the international C40 Mayors Climate Summit where discussions with other leading cities will center on climate solutions and the status of the Paris Climate Agreement.