As New York city Mayor Michael Bloomberg enters the final stretch of his long tenure, he has turned his attention to legacy-building. Cornell-Technion is one manifestation of this “edifice complex,” but in a recent address on protecting the five boroughs against future storm surges, the mayor offered an idea far more ambitious and far more promising: he called for the creation of a new neighborhood along Manhattan’s eastern edge, a “Seaport City” to be built on landfill, much like Battery Park City on the west side. The following (felicitously titled “Southern Manhattan Initiative 2″) is drawn from the city’s report on “A Stronger, More Resilient New York“:

The eastern edge of Lower Manhattan, particularly from the Battery north to Chinatown, is one ofthe lowest-lying areas in Southern Manhattan and is, therefore, subject to flooding. This vulnerability, demonstrated during Sandy, is likely to get worse as the climate changes. Though the integrated flood protection system described above could provide substantial protection during extreme weather events, there may need to be a longer-term approach that not only could offer more permanent protection,butalso,overtime,couldbeself-financing. Subjecttoavailablefunding,theCity,therefore, will study the creation of a new multi-purpose leveealongtheeasternedgeof LowerManhattan from the Battery Maritime Building to Pier 35, which would provide protection against multipleclimatechange-related threats,including storm surge and sea level rise. This approach would provide the protective value of a traditional levee while also providing new land on which commercial and residential buildings could be constructed, both to accommodate the City’s growth and to help finance the construction of the multi-purposelevee. The intention would be for this new East River neighborhood to serve much the same function as Battery Park City does along the Hudson River.

Though not quite as conceptually ambitious as “LoLo,” Vishaan Chakrabarti’s vision of a new neighborhood that would link Battery Park and Governor’s Island, Seaport City is an excellent idea for a city that is severely capacity-constrained. While other coastal global cities, like Tokyo, have expanded their footprint through landfill development in recent decades, Manhattan hasn’t seen a major expansion since Battery Park City, the landfill portion of which was completed in 1976. New York city has grown considerably since then — that year, the population was 7.4 million; the latest estimate is just over 8.3 million. The city has also grown considerably more affluent, and affluent consumers tend to consume, and certainly to prefer to consume, more living space. High housing prices suggest that the demand for New York city greatly outstrips the supply, so one natural solution is to increase supply through the use of landfull development. If anything, my criticism of the Seaport City concept is that it is not sufficiently ambitious. Though historical preservationists, environmentalists, and NIMBYs and BANANAs of all stripes would surely howl in derision, there is a strong case for Seaport City and LoLo. The only coherent case against is that we ought to prioritize upzoning existing neighborhoods before we commit to expanding Manhattan, though of course this neglects the ways in which landfill development will help protect the city from coastal flooding, etc. Both strategies ought to be vigorously pursued. Environmental objections to landfill development are particularly fatuous, given the environmental benefits of dense urban living, as described by Harvard economist Edward Glaeser:

New York City has the largest gap in emissions between central city and suburbs of any metropolitan area in the country—unsurprisingly, since New York’s central city is the epitome of dense urban living. Our estimate is that an average New York City resident emits 4,462 pounds less of transportation-related carbon dioxide than an average New York suburbanite. The reductions in carbon emissions from home heating and electricity are comparably large, thanks to New York’s famously tiny apartments. Manhattan is one of the greenest places in America.

And though congestion is a legitimate concern, a combination of congestion pricing and investment in mass transit can help mitigate any downsides. New York city’s size and productivity is a crucial strategic asset for the U.S. Increasing its size will tend to increase its productivity, per the literature on superlinear scaling. We would be foolish not to pursue this opportunity.