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It’s for good reason Boston and Cambridge have earned strong reputations as leaders in sustainable building practices. In 2007, Boston amended its zoning code to become the first city in the nation to require LEED standards for all large-scale development projects. Cambridge followed suit in 2010, and along the way both cities were quick to adopt the Stretch Energy Code, an optional provision that requires greater energy efficiency in the design of most new buildings.

In May, Boston once again took the lead when its City Council approved Mayor Tom Menino’s proposal for a Building Energy Reporting and Disclosure Ordinance. Drawing on lessons learned from similar initiatives already under way in other cities, this will encourage greater efficiency measures by requiring all large and medium-sized buildings to report their annual energy and water use.

Meanwhile, on the other side of the Charles River, climate advocates and neighborhood leaders have been pushing the Cambridge City Council to go even further – by adopting a comprehensive requirement for “net zero” greenhouse gas emissions in the annual operation of all large, new buildings.

The movement for a “Net Zero Cambridge” took a big step forward Oct. 21, when the City Council approved the “Getting to Net Zero” framework, a proposal by City Manager Richard C. Rossi to put Cambridge on the path toward becoming a net zero community.

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This latest milestone is the culmination of a series of meetings that Cambridge Mayor Henrietta Davis affectionately dubbed “Net Zero Emissions Month” – and it comes as a direct response to the grassroots activism of some 500 residents who signed on to support the Connolly Petition, a citizens’ zoning amendment for net zero emissions that, in the words of one local reporter, “has come to dominate the city’s calendar” since being introduced to officials June 24.

The most striking feature of the net zero emissions proposal is the requirement that all of the energy consumed by large, new buildings must come from renewable sources, such as wind or solar power. In the event that fossil fuel-based energy is needed, it must be offset through the purchase of renewable energy certificates or some other form of local carbon mitigation. To help with compliance, the net zero proposal also calls on Cambridge to implement its own scheme for annual energy use reporting.

According to the city’s Community Development Department Web page for sustainable buildings, 80 percent of the city’s greenhouse gas emissions come from building energy consumption.

In essence, the renewable energy requirement is the next big piece of the building emissions puzzle. LEED building standards, the Stretch Energy Code and energy use reporting all serve to promote greater efficiency and awareness, thereby driving down overall energy consumption. In turn, the renewable energy requirement ensures that energy consumed at the building level will not add to the net concentration of carbon in the atmosphere.

Critics of the Connolly petition have often confused the proposal for net zero emissions with a far more challenging concept known as net zero energy.

The confusion over terminology is understandable. Standardized definitions of “net zero” have yet to be established, and in 2008, Gov. Deval Patrick formed a task force to focus on net zero energy buildings (i.e., buildings that are designed to produce all of the energy they consume). In the end, net zero energy was deemed to be a viable statewide target for the year 2030.

On the contrary, we can strive for net zero emissions right now. This is because renewable sources of energy are available over the grid at very competitive prices. For example, the nonprofit Mass Energy Consumers Alliance is offering 100 percent renewable electricity to Cambridge residents for just 2.7 cents more per kilowatt hour as compared with Nstar’s basic rate. In March, Palo Alto, Calif., took the leap and adopted a 100 percent renewable portfolio for all residents.

To be sure, maintaining the net zero emissions standard will not be easy, but from a business perspective there’s good reason to believe it’s worth the effort.

According to green building consultant Jerry Yudelson, the business case for net zero is compelling. In an interview with Energy Manager Today, Yudelson notes that, “large corporations are doing net zero to attract and keep staff of the millennial generation.”

For proof, Yudelson points to the 350,000-square-foot Genzyme Center in Kendall Square, which has sourced 100 percent of its electricity from local, renewable sources for nearly a decade. As a result, Genzyme has documented a reduced turnover in staff, creating savings that more than make up for the added cost of green power.