The Boston City Council unanimously adopted a new rule Wednesday requiring buildings 20,000 square feet or more — larger than half a football field — to reduce their carbon emissions to zero by 2050. Acting Mayor Kim Janey will sign the ordinance, a spokesperson said.

The zero-emissions measure, a crowning achievement of outgoing Jamaica Plain City Councilor Matt O'Malley, will impact about 3,500 commercial and residential buildings within the city of Boston.

O'Malley said the ordinance, which amends existing code, will put Boston among only a handful of cities that have mandated carbon neutral targets.

"This is going to make sure that Boston leads on not only energy efficiency, but building a cleaner, greener, safer city, commonwealth, country and planet for generations to come," he told reporters before the measure passed.

The provision establishes a schedule which will allow large buildings to gradually reduce greenhouse gas emissions in five-year increments beginning in 2025. The buildings are expected to reduce their emissions by 50 percent by 2030.

Additionally, the measure calls for establishing a nine-member review board, appointed by the mayor and approved by the council, to monitor compliance and impose penalties. Fines could reach to $1,000 a day and could result in legal action against owners alleged to be in violation.

Most of the buildings under the new ordinance, including GBH News' Brighton headquarters, have been required to track their individual emissions and water usage under a 2013 version of the measure.

O'Malley said the business community has been generally supportive of the environmentally conscious move. Anastasia Nicolaou, VP of Policy and Public Affairs for NAIOP Massachusetts, the Commercial Real Estate Development Association, agreed and said their group recognizes the importance of Boston's carbon neutrality goals.

"It's a great step the city council took today," she said, noting that NAIOP weighed in on the measure months before its passage.

More regulations will likely come up once the review board begins meeting and monitoring, Nicolaou added.