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The New York City Council passed a pioneering package of bills Thursday that seeks to drastically slash carbon emissions from thousands of buildings across the boroughs—marking a watershed moment in the city’s fight against climate change.

The bundle of six bills, known as the Climate Mobilization Act, is geared toward reducing the city’s planet-warming emissions by setting caps for a variety of building types, with the goal of achieving a 40 percent decrease in greenhouse gas emissions by 2030. Landlords who don’t adapt their buildings will face hefty fines.

The most dramatic measure would require buildings of more than 25,000 square feet—which are responsible for 30 percent of the city’s carbon emissions—to conduct retrofits, such as new windows and insulation, to make those buildings more energy-efficient. The aggressive bill is a crucial step toward protecting the city’s vulnerable costal communities, said the Queens Council member who spearheaded the legislation.

“There are talks about the Rockaways, Coney Island, and neighborhoods in Staten Island literally being wiped off the map by the end of this century if we do not act,” said Council member Costa Constantinides, who represents northern Queens, during Thursday’s vote. “No single-handed policy can completely reverse the effects of climate change, but this policy, when enacted, will be the largest emissions reduction policy in the history of New York City or any city anywhere.”

Come 2024, the legislation mandates landlords move toward cutting their building emissions 40 percent by 2030, and would put the city on a path toward reducing its carbon emissions by a whopping 80 percent by 2050. Such efforts are being mulled by states, New York among them, as Congress’s proposed Green New Deal—which seeks to tackle climate change and create high-paying jobs in clean energy—is debated across the nation.

“Our planet is closing in on a breaking point … we have to transition from investing in fossil fuel infrastructure to clean, renewable energy,” Council Speaker Corey Johnson said during the vote. “We have to act decisively and we have to act now.”

Advocates who fought for the act call its passage a “monumental moment.”

“This is New York’s ‘green new deal,’” said Pete Sikora, the director of climate and inequality campaigns with New York Communities for Change, told Curbed Thursday. “You cannot overstate how big a deal this is, there is no city world wide anywhere that has set emission limits on this scale.”

But Sikora notes that a major challenge will be expanding the mandate to buildings smaller than 25,000 square feet. Measures to do so will have to be more nuanced, so as not to spur rent increases or create unaffordable costs for mom-and-pop landlords, he said.

The act’s passage comes after years of spirited talks among environmental advocates, engineers, architects, and builders, and has faced fierce pushback from heavy hitters in the real estate industry, chiefly among them the Real Estate Board of New York, which argues the legislation places the burden of curbing the city’s emissions on larger properties. In a statement, REBNY president John Banks said he supported the goal of reduced carbon emissions, but called the reforms unbalanced.

“Unfortunately, Intro 1253 does not take a comprehensive, city-wide approach needed to solve this complex issue,” Banks stated. “[The bill] will fall short of achieving the 40 [by] 30 reduction by only including half of the city’s building stock.”

Certain building types, such as houses of worship, and buildings with rent regulated units and senior low-income housing will be expected to perform other energy-saving measures, such as insulating pipes and installing heat sensors. Hospitals will have their own specific set of conditions. City estimates have put the cumulative cost of retrofitting buildings for owners above $4 billion, though landlords are expected to have lower operating costs in the long run.

To aid property owners in making the retrofits, the act creates the Office of Building Energy and Emission Performance to oversee the implementation of the standards and to provide technical assistance. Another bill in the package forges a new program that will make building owners eligible for specific loans toward meeting the emission goals.

Mayor Bill de Blasio, whose administration has worked closely with the council on the package, said earlier this week he intends on signing the bills into law. The legislation is part of an ambitious $14 billion plan by the de Blasio administration to dramatically reduce the city’s carbon footprint. On Monday, City Hall released the “One NYC 2050: Building a Strong and Fair City” report as a blueprint to achieving a citywide 40 percent reduction in greenhouse emissions starting from a 2005 baseline by 2030.

To do that, the de Blasio administration unveiled several initiatives including banning all-glass facades in new construction unless builders meet certain performance guidlines, switching to 100 percent clean energy for city operations through Canadian hydropower and other sources, and working to improve air quality in congestion-heavy sections of the city by creating “People Priority Zones” to restrict vehicular access and create pedestrian havens—a stretch of Lower Manhattan would be the first.

“We have to go farther than we ever thought we could and we have to do it faster than we ever thought we would,” Mayor de Blasio said Monday as he announced his administration’s vision for the “NYC Green New Deal” in Long Island City. “This is no longer an option. This must be done.”