After much deliberation I've decided that there isn't much hope of New York remaining entirely habitable. No amount of alternative energies will prop this type of overgrown urbanism up. New York--and cities like it--needs hydrocarbons. Never mind keeping the cars running. Rail service will not operate at this scale on wind and water. All these lights, mechanical ventilators and elevators that keep acres of skyscrapers usable won't run on wind and water either. Understand that it is possible to power a handful of buildings, but not hundreds. Manhattan at the very least will be largely abandoned. There are plenty of low-rise, naturally lit and otherwise low-energy buildings on the island, but there are just as many high-energy ones whose abandonment may make plenty of neighborhoods desolate and dangerous. Even the more modest tenements that crowd the boroughs don't have very good prospects. A lot of the post war apartment buildings are over six stories high and at the very least may face sanitation problems if it becomes very expensive to pump water past the fifth floor. Too, many of these buildings weren't designed to allow natural light to filter into the common areas like hallways, stairwells and cellars. If generating electricity for light becomes troublesome, then these places will largely be in the dark while the city itself will be populated by increasingly desperate people. Just getting from the lobby to an apartment may become so dangerous that these buildings won't be used by anyone but the foolhardy. The big cities and their suburbs may become increasingly lawless and deadly until the final food shipments are made and everyone clears out. People who can afford to leave will do so and those left behind will be living in a no man's land, for a while at least. There may be pockets of civilization, but these will abut the dangerous areas. Even if a given neighborhood has features that allow it to be livable like small scale power generation, a large percentage of buildings under five stories, and wide scale urban horticulture, there would for a while be the danger of invasion from the denizens of dying areas.
The historic model for urbanization is one of cities (small by today's standards), towns and villages surrounded by farmland and separated by wilderness--a well-defined nucleus of permanent dwellings encased in an agricultural cytoplasm beyond which the ecosystem is left largely unmolested; The modern model is the industrial megacity surrounded by suburbs and exurbs; this organism tends to grow taller and denser in its center while its low density edge creeps out in an ever widening circle of raised ranch ruination. The latter will not gently drift back into the former. Those still in the cities and suburbs during energy descent will be far worse off than those in faraway towns and farms. Everyone is going to have a tough time of it during energy descent, but it is the metroplexes that will suffer disproportionately and be more prone to loss of life through violence. I worry that not even pockets of civility will remain in the vast swaths of land already covered by megalopolis. Some of the best sites for city-building may be lost for as long as it takes nature to digest the remains of the industrial wreckage. Global warming may have already be doing the job of submersing a lot of these soon-to-be-abandoned ruins anyway. Maybe in a thousand years coastal villagers in what is now Rutherford, NJ, will paddle their canoes around the spires of the Empire State and Chrysler Buildings. The essential truth is this; what we've built in our cities and our suburbs will be useless in the future when the energy available is simply not enough to keep it all running and livable.
The main problem is one of population and density. The inappropriate furnishings of the industrial city can be abandoned and replaced over decades and centuries. The inhabitants, however, would need to cobble together quickly other means of procuring food calories. One square mile of healthy agricultural land can support about two or three thousand human beings. There are nearly 9 million full-time residents of New York's 300 or so square land miles. That means about 3000 square miles of nearby farmland would be necessary to keep New York fed. Ironically, the "urban area" or suburban sprawl around New York proper is about 3000 square miles and home to another 10 million suburbanites. So all the nearby farmland that would be required to feed New York's millions have been ruined by suburbanization. The city itself is simply too big and populous anyway, even before we add in the suburban sprawl that knots the area into the chain of conurbation along the northeast coast. Megacities and megasuburbs would not have been possible without the energy density ("bang for the buck") of abundant hydrocarbon fuel. Such a concentration of people and resources requires an immense energy feed in order to hold together. During energy descent, the arrangement simply won't hold. Oil and natural gas are the binding agents keeping the urban mega-golem's parts together and without them the montrous patchwork will fall apart. The swollen populations of the big cities would have to melt back into smaller communities with nearby agriculture already established or relatively easily re-established. Whatever happens, the metroplexes will not be able to support anything resembling their current populations or any at all. This is precisely how the ruins of a once-powerful civilization are made. I think the ruins created by the industrial age may be the most impressive and outrageous the world will ever see.
As I write this there is an effort to remove cars entirely from 42nd St and install light rail. This fills me with nervous hope. If megalopolis were to devote itself to rescaling immediately, then we could avoid the scenarios of chaos and abandonment that populate my nightmares. At the same time, I have to wonder at any intended symbolism of laying light rail and sidewalks over the city's most famous street in the center of the center; it smacks of the proverbial laying of a band aid across a disembowlment. The destruction, disfigurement and other distortions (like living 40 miles from one's job or working in an office 200 ft off the ground) of the post-war industrial hypergrowth will not be easily corrected. Most of the skyscrapers-- especially the postwar glass cuboids-- would have to be demolished and replaced with sensibly scaled buildings made from lasting materials like brick and stone. In fact, the same holds for most all the postwar housing stock throughout the region. Just about all of that junk would have to go and be replaced by buildings with natural ventilation and lighting. That's a tall order and I really don't think it will be accomplished by means of public will or that it could even be accomplished within the energy window we have remaining. By the time the general public can no longer avoid the fact that things as they stand won't work in the future, we will likely be too energy-poor to do much about it. Yet, if cars were to be banned from the nexus of the biggest metropolis in the U.S. and light rail (more efficient than either buses or subways) installed in its place, then I would have to rethink the fate of megalopolis. We still face food shortages yet I also hear of farms being established within city limits and urban gardening is growing more popular. If a major American city makes such drastic moves toward lower energy usage and relocalizing food production, then one can't help but hope. On the other hand, residential skyscrapers are going up in my sister-neighborhood of Long Island City. I do maintain a small hope for this petroleum-spawned disaster, but I'm keeping an eye on the exits.