If cities are going to curb the rise of global temperatures to less than 2 degrees Celsius, they’ll have to address the single largest contributor, by sector, to their carbon footprint: buildings. Buildings account for roughly 50 percent of a city’s total carbon emissions, and 70 percent in major cities like London, Los Angeles, and Paris.

The ultimate goal, as laid out by the World Green Building Council at COP 21 in Paris in 2015, is that by 2050—when 68 percent of the world’s population is projected to live in urban areas—all buildings will only use as much energy as they generate. And to get there, a group of large cities is first tackling a closer target. Last month, the mayors of 19 cities—including New York, London, Tokyo, and Johannesburg—declared that they will enact policies and regulations that will make all new buildings carbon neutral by 2030.

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The bad news is that the larger challenge is to make existing, not new, buildings more efficient. Buildings that already exist today are estimated to account for 65 percent of all buildings in Organization for Economic Co-operation and Development countries come 2060.

Even so, changing how new buildings are built has major implications for the future. And fortunately, raising standards for new buildings—compared to retrofitting older ones—is the lower-hanging fruit. “New construction is potentially much easier, since you’re starting from scratch,” said Ralph DiNola, CEO of the New Buildings Institute, a nonprofit that advocates for better energy performance in buildings. Not that there won’t be any challenges, DiNola added, but carbon neutrality “is a good and realistic goal as long as we are clear about what that requires for the buildings.”

For starters, cities need to have in place a climate action plan; robust building codes that keep up with energy-efficient technology and design; and energy-intensity targets that will guide buildings toward zero carbon emissions, said DiNola. The New Buildings Institute works with New York and other cities to develop “stretch codes”—an extra layer of local, more stringent regulations on top of the base building codes, which focus specifically on energy efficiency. Cities also need to set up a system of rewards and penalties, and give builders and developers enough time to comply.

Keep reading on CityLab.com

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