by Henrietta Davis and Joan Fitzgerald Boston has set a goal to be carbon neutral by 2050. Since Boston’s buildings produce more than 70 percent of the city’s carbon emissions, this goal cannot be reached without much stronger building energy-efficiency standards than we have now. These standards must also reduce and eventually eliminate fossil fuels in the building’s power supply for heat, light and appliances. Boston City Councilor Matt O’Malley is trying to effect that change. (And none too soon: Last week, the U.N.’s Intergovernmental Panel on Climate Change issued a report warning of catastrophic results by 2040 unless dramatic and unprecedented measures to reduce carbon emissions are taken.) He is working with other council members and advocates to develop regulations and incentives that would move Boston toward a new "net-zero" carbon emissions standard for buildings. The net-zero carbon standard is a variation on something called zero-net energy (ZNE), which means a building gets all the energy it uses from renewable energy produced on site. (The challenge is, once you get beyond three or four floors high, it is difficult to produce sufficient energy on site.) In most cases, the standard for high-rise buildings is net-zero carbon — meaning that any carbon emissions produced by the building’s power consumption are offset by purchasing renewable energy that displaces power produced by fossil fuels. Some people, including Boston Mayor Marty Walsh, say the net-zero standard Councilor O’Malley is advocating for is not technologically possible. A piece in the Boston Herald by Jordan Graham, about the net-zero standard, quotes Mayor Walsh equivocating and David Begelfer, chief executive of NAIOP Massachusetts, a commercial development association, saying “To make it net-zero, they’d love to do it, but the technology’s not there yet.” This is wrong. It is not only technologically possible — it can be done at little incremental cost. In 2009, the European Union mandated that countries set standards to achieve nearly zero emissions in all new buildings by the end of 2020 and offers a standard format for nations to report progress. Several European cities, including Hamburg, Copenhagen and Stockholm among them, require net-zero energy for some or all buildings. By 2020, California will require all new residential or single-family homes to be net-zero energy. U.S. cities that are proposing similar standards for some or all buildings include Salt Lake City; Palo Alto, Santa Monica and Santa Clara, California; and Fort Collins and Boulder, Colorado. In Massachusetts, Cambridge — where one of us served as mayor — has committed to a net-zero emissions plan that calls for all buildings to produce, on site, all the electricity they require from renewable sources by 2040. The plan may ultimately allow for exceptions for some buildings (to be handled by bundling buildings that produce excess renewable energy with non-compliant buildings) or allow developers to buy carbon offsets. Building a net-zero carbon emissions building is fairly simple: Build to the highest energy-efficient standards; design the building to use electricity for heating, lighting and appliances; purchase renewable energy as the power source — either by buying green power (e.g. wind, solar, geothermal, hydroelectric) from a utility, such as Eversource, or from another supplier. Larger operations, such as universities and hospitals, typically go the offset route. Boston Medical Center is a great example of this: BMC partnered with MIT to buy solar power from North Carolina to offset its fossil fuel use. It’s true that renewable energy currently costs slightly more than fossil fuels. However, aggressive energy-efficiency measures reduce a building’s energy demands significantly, meaning they use far less energy. Several studies estimate that zero-emissions buildings cost the same or modestly more to construct, but that their reduced operating costs make them more profitable over the life of the building. Cities are also experimenting with different incentives to encourage developers to build a net-zero emissions way. For example, Cambridge is considering giving developers the chance to build more square footage than is currently permitted by zoning regulations (called a “density bonus”) in exchange for building to a net zero standard. Swedish cities convene working groups of city planners, architects, developers and builders to regularly discuss how to cost-effectively build to zero-emissions standards. As a result, Sweden is home to some of the world’s leaders in highly energy efficient construction. Boston should be able to do something similar. If Boston is going to achieve its stated goal of going carbon neutral by 2050, it will take a carefully crafted implementation plan involving owners, tenants, policy makers and others. Councilor O’Malley’s proposals include important steps toward the ultimate goal — zero carbon emissions from buildings by 2050. But many, many more steps will be needed and as the latest report from the IPCC states, we need to get to carbon neutrality sooner than 2050.