With higher seas, a common storm could prove as damaging as the rare big storm or hurricane is today, scientists say. Were sea levels to rise four feet by the 2080s, for example, 34 percent of the city’s streets could lie in the flood-risk zone, compared with just 11 percent now, a 2011 study commissioned by the state said.

New York has added bike lanes, required large buildings to track and reduce their energy use, banned the dirtiest home heating oils, and taken other steps to reduce the emissions that contribute to global warming. But with shoreline development that ranges from public beaches to towering high rises — and a complex mix of rivers, estuaries, bays and ocean — the city needs to size up the various risks posed by rising seas before plunging ahead with vast capital projects or strict regulations, city officials argue.

Yet the city’s plan for waterfront development dismisses any notion of retreat from the shoreline. Curbing development or buying up property in flood plains, as some smaller cities have done, is too impractical here, city officials say, especially because the city anticipates another million residents over the next two decades.

Rather, the city and its partners are incorporating flood-protection measures into projects as they go along.

Consolidated Edison, the utility that supplies electricity to most of the city, estimates that adaptations like installing submersible switches and moving high-voltage transformers above ground level would cost at least $250 million. Lacking the means, it is making gradual adjustments, with about $24 million spent in flood zones since 2007.

Some steps taken by city agencies have already subtly altered the city’s looks. At Brooklyn Bridge Park, a buffer between the East River and neighborhoods like Dumbo, porous riprap rock and a soft edge of salt-resistant grass have been laid in to help absorb the punch of a storm surge. Sidewalk bioswales, or vegetative tree pits that can fill up with rainwater to reduce storm water and sewage overflows and also minimize flooding, are popping up around the city.

Over all, the city is hoping to funnel more than $2 billion of public and private money to such environmental projects over the next 18 years, officials say.