How Sea Level Rise Will Affect New York

Let’s try answering this question on Quora:

How will global warming, and particularly sea level rises, affect New York City?

I doubt sea level rise will be the first way we’ll get badly hurt by global warming. I think it’ll be crop losses caused by floods, droughts and heat waves, and property damage caused by storms. But the question focuses on sea level rise, so perhaps we should think about that… along with any other ways that New York City is particularly susceptible to the effects of global warming.

Suppose you know a lot about New York, but you need an estimate of sea level rise to get started. In the Azimuth Project page on sea level rise, you’ll see a lot of discussion of this subject. Naturally, it’s complicated. But say you just want some numbers. Okay: very roughly, by the end of the century we can expect a sea level of at least 0.6 meters, not counting any melting from Greenland and Antarctica and at most 2 meters, including Greenland and Antarctica. That’s roughly between 2 and 6 feet.

On the other hand, there’s at least one report saying sea levels may rise in the Northeast US at twice the average global rate. What’s the latest word on that?

Now, here’s a website that claims to show what various amounts of sea level rise would do to different areas:

•, Flood maps, including New York City.

Details on how these maps were made are here. One problem is that they focus too much on really big sea level rises: the smallest rise shown is 1 meter, then 2 meters… and it goes up to 60 meters!

Anyway, here’s part of New York City now:

Here it is after a 1-meter (3-foot) sea level rise:

(Click to enlarge any of these.) And here’s 2 meters, or 6 feet:

It’s a bit hard to spot the effects in Manhattan. They’re much more noticeable in the low-lying areas between Jersey City and Secaucus. What are those: parks, industrial areas, or suburbs? I’ve heard New Yorkers crack jokes about the ‘swamps of Jersey’…

But of course, a lot of the city is underground. What will happen to subways and other infrastructure, like sewage systems? And what about water supplies? On coastlines, saltwater can infiltrate into surface waters and aquifers. Where does freshwater meet saltwater near New York City? How will the effect of floods and storms change?

And of course, there are other parts of New York City these little maps don’t show: for those, go here. But watch out: at first you’ll see the effect of a 7-meter sea level rise… you’ll need to change the settings to see the effects of a more realistic rise.

If you live in a place that will be flooded, let me know!

Luckily, we don’t have to figure everything out ourselves: the state of New York has a task force devoted to this. And as task forces do, they’ve written a report:

• New York Department of Environmental Conservation, Sea Level Rise Task Force, Final Report.

New York City also has an ambitious environmental plan:

• New York City, PlaNYC 2030.

Finally, let me quote part of this:

• Jim O’Grady, Sea level rise could turn New York into Venice, experts warn, WNYC News, 9 February 2011.

Because it looks ahead 200 years, this article paints a more dire picture than my remarks above:

David Bragdon, Director of the Mayor’s Office of Long-Term Planning & Sustainability, is charged with preparing for the dangers of climate change. He said the city is taking precautions like raising the pumps at a wastewater treatment plant in the Rockaways and building the Willets Point development in Queens on six feet of landfill. The goal is to manage the risk from 100-year storms—one of the most severe. The mayor’s report says by the end of this century, 100-year storms could start arriving every 15 to 35 years.

Klaus Jacob, a Columbia University research scientist who specializes in disaster risk management, said that estimate may be too conservative. “What is now the impact of a 100-year storm will be, by the end of this century, roughly a 10-year storm,” he warned.

Back on the waterfront, oceanographer Malcolm Bowman offered what he said is a suitably outsized solution to this existential threat: storm surge barriers.

They would rise from the waters at Throgs Neck, where Long Island Sound and the East River meet, and at the opening to the lower harbor between the Rockaways and Sandy Hook, New Jersey. Like the barriers on the Thames River that protect London, they would stay open most of the time to let ships pass but close to protect the city during hurricanes and severe storms.

The structures at their highest points would be 30 feet above the harbor surface. Preliminary engineering studies put the cost at around $11 billion.

Jacob suggested a different but equally drastic approach. He said sea level rise may force New Yorkers to pull back from vulnerable neighborhoods. “We will have to densify the high-lying areas and use the low-lying areas as parks and buffer zones,” he said.

In this scenario, New York in 200 years looks like Venice. Concentrations of greenhouse gases in the atmosphere have melted ice sheets in Greenland and Antarctica and raised our local sea level by six to eight feet. Inundating storms at certain times of year swell the harbor until it spills into the streets. Dozens of skyscrapers in Lower Manhattan have been sealed at the base and entrances added to higher floors. The streets of the financial district have become canals.

“You may have to build bridges or get Venice gondolas or your little speed boats ferrying yourself up to those buildings,” Jacob said.

David Bragdon is not comfortable with such scenarios. He’d rather talk about the concrete steps he’s taking now, like updating the city’s flood evacuation plan to show more neighborhoods at risk. That would help the people living in them be better prepared to evacuate.

He said it’s too soon to contemplate the “extreme” step of moving “two, three, four hundred thousand people out of areas they’ve occupied for generations,” and disinvesting “literally billions of dollars of infrastructure in those areas.” On the other hand: “Another extreme would be to hide our heads in the sand and say, ‘Nothing’s going to happen.’”

Bragdon said he doesn’t think New Yorkers of the future will have to retreat very far from shore, if at all, but he’s not sure. And he would neither commit to storm surge barriers nor eliminate them as an option. He said what’s needed is more study—and that he’ll have further details in April, when the city updates PlaNYC.

Jacob warned that in preparing for disaster, no matter how far off, there’s a gulf between study and action. “There’s a good intent,” he said of New York’s climate change planning to date. “But, you know, mother nature doesn’t care about intent. Mother nature wants to see resiliency. And that is questionable, whether we have that.”

29 Responses to How Sea Level Rise Will Affect New York

  1. So its good to see both the conservative estimates and others critical take on this issue. They are made from global mean projections of temperature

    This is unsuitable for local and regional scales. As mentioned by the book “Climate Change Adaption in the Water Sector, Global Climate Models (GCM) are too coarse and that is why you get rough estimates.Still good but not useful for capacity planning , so you need to create high-resulotion regional climate models with sizre 500-1000 km. See references on this page:

  2. Nathan Urban says:

    Downscaling is somewhat less of a problem for sea level than other variables like temperature and (especially) precipitation, since sea level rise is a sort of global phenomenon. There are local variations in sea level rise, but the century-scale uncertainty in them is probably dominated by the uncertainty in the global mean response due to ice sheet dynamics and overall amount of warming.

    That being said, a few references on regional sea level responses include Yin et al. (2009) and Yin et al. (2010) on changes in regional ocean circulation, Gomez et al. (2009) on regional effects of Antarctic ice sheet disintegration, Kopp et al. (2010) on regional “fingerprints” of Greenland ice sheet melting, and Gutierrez et al. (2011) on statistical prediction of local shoreline impacts.

  3. Phil Henshaw says:

    Na… It just floods. Regional coast lines were not made to be waterproof. We’ll lose the subway system quick enough if the water can’t drain, etc, etc.

    • Speed says:

      The Netherlands is a geographically low-lying country, with about 25% of its area and 21% of its population located below sea level and 50% of its land lying less than one metre above sea level. Significant land area has been gained through land reclamation and preserved through an elaborate system of polders and dikes.

      • Phil Henshaw says:

        Are there differences? Is the Netherlands still able to drain its land at low tide, for example? Is the real problem in the offing one that even the Netherlands will no longer be able to hold back?

        Is there also various scale changes for the US cost? Are there several major river systems to elevate or re-engineer? Is there an extraordinarily long and highly complex shoreline, with much of our most valuable real estate, to either move or wall in?

        I think the gigantic economic problems, not the theoretical ones, are the real difficulty. Abandoning what’ll get wet and building some more sophisticated sustainable habitat seems definitely the low cost scheme to me.

        My being an architect with a lifetime of experience with building and development problems doesn’t make my hunches certain of course, but that’s my hunch of what will happen. I’m assuming that when people get down to having to spend real money for this stuff they’ll realize that the 200 year plan has to be for 30 or 40 feet of ocean rise, something like that, and that it would be dumb to spend the money twice.

  4. Speed says:

    I’m afraid that the maps showing the effects of one and two meter rises in sea level on Manhattan Island assume no change island itself — there will be no progress in infrastructure or use of the waterfront real estate.

    Historically the shoreline has been anything but static. No longer can anyone walk down to the beach and dip a toe in the cool water. No ice skating in winter. All the physical/commercial infrastructure is used up and replaced every few decades as ships get bigger and uses change. If allowed, landowners would have long ago moved seawalls further and further into the rivers, filling behind to create more valuable and useful real estate.

    “Castle Clinton, a circular red sandstone fort built in 1807 on what was then an offshore spit of rocks. Countless fills by the land-hungry city have left it a few hundred feet inland.”

    Certainly as this process continues in the future, seawalls will be made incrementally taller and land will be filled. It’s not a tsunami we’re facing. It’s more like a leaking faucet.

    “I See a Ship in the Harbour – Part 1 – The Living Harbour”

    • Phil Henshaw says:

      Yes, it is important to understand the problem as a quite gradual rise, a “leaking faucet” in your phrasing. That a shoreline is not made as a waterproof barrier, though, but just to lift you above water level, implies that the “build a tub” approach would be a temporary fix. That would start with barriers that only need to protect against high tide for a few hours a month then more and more over time.

      Two of the long term issues I think that makes important are 1) identifying the thresholds where existing urban infrastructure will not be possible to protect, and 2) the cost/benefit ratio of slowing the progress of the seemingly inevitable loss of our most ancient of investments in shoreline development. It might actually be best to just have a well planned move instead of in large sinking investments with no return.

      The most important issues, of course, remain to really understand 3) why the present economic model requires ever accelerating increases in energy us to remain stable (and un-steerable on approaching limits) and 2) the cultural traps that have for so very long been preventing discussion of that.

      • Speed says:

        Re: waterproof barrier — see link above about Holland.

        Perhaps you could supply us with an economic model that uses ever accelerating decreases in energy. Numbers please. A spreadsheet would be nice.

        With respect to shoreline development — Currently the world’s most valuable property is along the shore because of its beauty, recreation potential and … commercial use especially transportation and industries that depend on transportation. The most efficient mode of freight transportation is rail and the second most efficient is marine. The shore is where the two meet — trains can’t operate on water and boats require it.

        Are you telling us that it would be more economical to move all the current shoreline development inland than to raise the breakwall a meter or two?

        If you examine the shoreline of Manhattan or any other commercial area you’ll see seawalls and various other barriers that keep the water out and the land in. Building them three feet taller to further protect the commercial development behind them should be a financial no-brainer.

        And then we have the recent spate of land “reclaimed” from the oceans for commercial use. For example …

        Hong Kong International Airport was built on a large artificial island, formed by levelling Chek Lap Kok and Lam Chau islands (3.02 km² and 0.08 km² respectively), and reclaiming 9.38 km² of the adjacent seabed. The 12.48 km² airport site added nearly 1% to Hong Kong’s total surface area, connecting to the north side of Lantau Island near Tung Chung new town.

  5. Yes Speed that is what this adaptation page is all about, but the issue here
    is about how sea rise will affect NYC. See the first ref that Nathan Urban
    refers to:

    “We conclude that together, future changes in sea level and ocean circulation will have a greater effect on the heavily populated northeastern United States than estimated previously”

    So the question is how much more, and how that will affect NYC beaches and economically through adaptive measures like seawalls. But they are extremely expensive!

  6. Well, it is always good to see some actual data. Fortunately we have an almost continuous dataset for the New York tide gauge in PSMSL between 1993 and 2009.

    It is 117 years. Average rate of sea level rise is 2.95 mm/yr, acceleration is 0.005 mm/yr^2. In other words, there is no acceleration whatsoever, sea level change is linear at New York.

    At this rate average sea level will be 26-30 cm higher at Battery Park, Manhattan by the end of this century. Difference between low and high tide is about 1.5 m there.

    • John Baez says:

      Berényi wrote:

      Well, it is always good to see some actual data.

      I agree! I am sorry that I haven’t been able to help you settle your earlier question about sea level rise. I haven’t forgotten it. You or I should add that question to the Azimuth page Sea level rise, and/or ask some experts.

      Here are some pictures from the Permanent Service for Mean Sea Level page.

      New York monthly mean sea level data:

      New York annual mean sea level data:

      What happened in the late 1800s? A financial crisis or something?

      You’re right that this looks roughly linear, at least by eyeball. However, the accelerating melt of Greenland and Antarctica is only claimed to exist starting around 1992, so one has to be careful: that that might be true yet obscure in these graphs going back to 1860.

      Furthermore, if it’s really true that sea levels may rise in the Northeast US at twice the average global rate, then tricky things are going on, so we have to be even more careful in trying to relate the situation in Antarctica and Greenland to what’s going on in New York.

      I don’t have strong opinions about these issues; I just want to point out some potential pitfalls.

      • Nathan Urban says:

        Yes, it is a bit tricky to get regional sea levels. (Maybe I implied differently earlier; what I mean is that there are regional effects, but you don’t necessarily have to downscale below grid resolution to get an idea of what they are.)

        Beyond the global sea level rise, there are regional differences in thermosteric expansion, regional dynamical ocean circulation changes, regional gravitational geoid effects from ice sheet mass loss, and local glacial isostatic adjustment of the coastline.

        If you look at Figure 2e of the Kopp paper I cited, you can see a computer experiment where they looked at the combined effect on NYC of MOC changes in the Atlantic due to freshwater input and gravitational geoid effects from Greenland melting. The former induces above-average SLR at NYC (the effect discussed in the Yin paper); the latter induces below-average SLR. The net effect is below average SLR at NYC. Of course, this is all contingent upon the particular North Atlantic freshwater inputs and Greenland melt rates they imposed.

  7. Speed says:

    John Baez asked,
    “And what about water supplies? On coastlines, saltwater can infiltrate into surface waters and aquifers. Where does freshwater meet saltwater near New York City? How will the effect of floods and storms change?”

    “Each day, more than 1 billion gallons of fresh, clean water is delivered from large upstate reservoirs – some more than 125 miles from the City – to the taps of nine million customers throughout New York state.”

    The NYC aquifer is far from the coast and salt water.

    • John Baez says:

      Okay, good. I figured it was… New York City is famous for its water quality… but the New York State website mentioned the danger of salt water infiltrating aquifers, so I wanted to be sure. I guess they think that could be a problem in other communities in the state.


      • Frederik De Roo says:

        From US Geological Survey :

        Atlantic Coastal Plain – In Nassau and Suffolk Counties, Long Island, New York, pumping water for domestic supply has lowered the water table, reduced or eliminated the base flow of streams, and has caused saline groundwater to move inland.

        • Speed says:

          None of New York’s five boroughs is in Nassau or Suffolk Counties.

        • streamfortyseven says:

          In a time of long past peak oil, such as 30 years from now, unless people/corps/governments decide to build lots of thorium nuclear reactors or find another equally productive energy technology, the carrying capacity of Nassau and Suffolk Counties will drop sharply, along with their populations, and the aquifers will get a chance to recharge.

          It’s not just the sea level rising, it’s that and the depletion of energy-dense fuels such as petroleum products and …

  8. John Baez says:

    I was really hoping that some native New Yorkers would chip in here… technical expertise is great, but local knowledge is also great.

    When it floods, what happens?

    Are they building new stuff on reclaimed land that’s low-elevation?

    Do you know of any attempts to plan ahead for sea level rise?

    Etctera… don’t be intimidated by the people who post very scholarly comments. You’re New Yorkers! You’re supposed to be brash!

    (“Speed” here seems to fit that description.)

    • Hi,

      I am not shy, but I also don’t have much to say, so let me just make some guesses on how I would feel most impacted.

      When it floods:

      It seems by above discussion that the financial district gets gondolas. Unfair, but they are making the money. So what do we lose? Battery park, an easy connection between the west side highway and FDR drive, but the buildings are built on an extremely strong bedrock as far as I know, which is what makes Manhattan so special, right?

      Central Park seems safe from rising water levels, but it is a non-bedrocky area of Manhattan, right? In particular, it was once rather swampy back when everyone lived pretty far below 60th street.

      The north/north-east sides of Brooklyn are industrial and can probably deal with water. The Russians and Italians, among many others, could lose the beach and marinas on the other side of the borough.

      What happens in the South Bronx and the western edge of queens? I don’t know. We lose the birthplace of a lot of good hip-hop. Same goes for Staten Island, but I guess people will take refuge on higher ground (landfills).

      Are they building new stuff:

      No idea, but I would like to hear from someone who does. Maybe I’ll try to recruit some people with (more) useful remarks.

      @Speed: It’s true that neither Nassau nor Suffolk county contain any of the 5 boroughs, but its worth thinking about them when thinking about NYC. In particular, it is just a matter of historical events that Nassau is separate from Queens. I am not trying to be more technical, I am just suggesting that it might be useful to be a little less technical.

  9. Speed says:

    A few links that might be interesting.
    NYC Hazards: Coastal Flooding

    CDC Surveillance of Deaths Attributed to a Nor’easter — December 1992

    Co-op and Condo Monthly: New York is an Island
    Is your Buiding in a Flood Zone?
    “Not all flooding is caused by such dramatic events. Eric Cohen, a managing partner of Benefit Quest Inc., says flash flooding brought about by thunderstorms or intense rainstorms—where a local street can suddenly become a river—claims more than 140 lives a year.”

    U.S. Department of the Interior
    U.S. Geological Survey
    December 11-12, 1992, in New Jersey

    Manhattan, like most other cities in the Northeast has areas that flood periodically — more often from rain than seawater. As the sea level rises, which it has for more than 10,000 years, people and institutions will adapt. We’re clever that way.

    • Speed says:

      Clarification. A link above refers to 140 deaths per year from flash floods. This appears to be a national (US) statistic, not NYC or Manhattan.

      This from the National Weather Service makes more sense.
      Thunderstorm Hazards — Flash Floods
      “While the number of fatalities can vary dramatically with weather conditions from year to year, the national 30-year average for flood deaths is 127. That compares with a 30-year average of 73 deaths for lightning, 68 for tornadoes and 16 for hurricanes.”

      Note to John Baez … Are HTML tags supported in user comments?

      • John Baez says:

        Thanks for the clarification. 140 deaths per year from flash floods in NYC did seem amazingly high. I wonder how many there actually are, there, on average. 1?

        Yes, HTML tags are supported in comments; that’s how people make nice links, boldface, italics, quotes, etcetera. Unfortunately I’m the only person who can include images in comments: presumably that’s some sort of anti-advertising measure on the part of WordPress.

  10. Phil Henshaw says:

    I’m a New Yorker, and I replied. In practical terms, I don’t think coast lines are meant to be waterproof, they’re meant to tell you where your feet are above water. Long Island is a big sandbar, very permeable, so probably many municipal wells have gone below future sea level, for example. There’s a limit to how much you can pump, like when all sewers outlets have to turned into pump stations. It won’t be affordable is my guess.

    What I think you really need to know for New York is when major infrastructure will be compromised, like the sewers, subway, power distribution and all that. I suspect it’s when more than barriers to hold back high tide are needed, that I gather is somewhat over 100 years.

    I don’t know the data and understand the wide variation in projections, but I think the planning for what to abandon and dismantle (as nothing is likely to be moved or rebuilt) will need to take place before the end of the century. The reason nothing will be rebuilt is that it’s all too expensive, particularly in the rapidly declining EROI economy we’re running into, unexpectedly early, and ballooning mitigation costs for all our horrible long range environmental and technology planning, and without growth to pay for them.

  11. Christina Sormani says:

    Another thing to keep in mind is that storm surges destroy infrastructure, so that long before the sea level premanently floods a neighborhood, the neighborhood has been destroyed in a hurricane. See the images of Hurricane Sandy (2012). The governor of New York has offered to buy out homes in destroyed neighborhoods at prehurricane prices but is not mandating that people move. After the next hurricane one can expect a similar offer with houses at a much lower real estate value. This beach and waterfront land would then become state park land and a flood zone.

    As for Manhattan, much of the endangered land is on landfill already and one could raise the walls around these areas higher (or insist the next developments fill in the ground level significantly higher. It makes no sense that Battery Park City was built so close to water level, when an extra ten to twenty feet of above sea level land fill could have been used. Now people are more aware that future landfill needs to be done higher. Nevertheless apartments in Battery Park City go for millions of dollars.

  12. you left out one big thing. 0.6 to 2.0 meters is the SLR from melting ice. Add 3 meters on top of that from the increasingly likely failure of the West Antarctic Ice Sheet. and that rise would come suddenly – possibly in less than one year.

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