71,000 New Yorkers: “Rise Does Matter!”

Superstorm Sandy produced record storm surge levels for locations in and around the NY City metropolitan region. One way that global warming made Sandy worse is because global warming is causing sea levels to rise. Sea levels have risen more than a foot in the New York City region since the Industrial Revolution. So what difference did this extra foot make for the citizens of New York City? Quite a lot. 6,000 more people impacted for each inch of rise!

70,929 more people and 30,551 more homes flooded.

8ft surge vs. 9 ft surge for New York City residents

I asked storm surge expert Dr. Ben Strauss to reflect on what this extra foot meant for New Yorkers. His reply appears below (with permission):

According to NOAA’s preliminary tide gauge readings, Sandy peaked at 9.15 ft above Mean High Water (MHW, the average high tide line) at The Battery in NYC. Surging Seas uses the same elevation reference, MHW. So from our tool you can see we estimate that in NYC alone, ~633k people live on, and ~273k homes sit on, land that’s less than 9 ft above MHW. Compare that to 8ft, or one foot less: ~562k people and ~242k homes. So, yes, Sandy’s damage would absolutely still have been unthinkable without the extra 8 inches or so we might attribute to warming since the late 19th century. But you add about 6k people per vertical inch in this 8-9 ft elevation range. I think we all would have been happy to see just a few percent less damage here!

A few other thoughts:

• flood damage increases more steeply than flood depth
• how many pieces of infrastructure might have been saved if the water were a bit lower?
• a relative of mine heard a CBS news radio report that the water got 1.5 ft higher than anyone at Con Ed had ever imagined/planned for — I don’t know the exact wording. Would the 14th St transformer station that exploded and left so much of lower Manhattan in the dark — would it have exploded with 8 inches lower water? (est. global sea level rise since 1880) 15 inches? (est total NYC SLR since 1880, including local land subsidence)

Sea level rise is certainly not the main story line here, but it contributed to the total damage from flooding and surge without any doubt. Furthermore, Sandy provides an illustration of flood levels that could be common — say, once a decade or worse toward the end of this century — if the upper end of sea level rise projections for NYC are realized.

Dr. Ben Strauss serves as Chief Operating Officer and Director of the Program on Sea Level Rise at Climate Central. In the latter capacity, he has published multiple scientific papers, testified before the U.S. Senate, authored the Surging Seas report, and led development of the SurgingSeas.org coastal flood risk tool, leading to front-page coverage in the New York Times and Washington Post, appearances on NBC, ABC, CBS, PBS and NPR national programming, and extensive coverage nationwide, from AP, Reuters, Bloomberg, USA Today and the LA Times, to many hundreds of local news outlets, to numerous editorials and op eds.

In the future, we will look back at the one foot sea level rise as “the good old days”. According to the New York State Sea Level Rise Task Force Report, it is very possible that seas will rise an additional 2.5 ft by the 2050s and 4.5 ft by the 2080s. Imagine what a Sandy would do then? It is pretty clear that New York City planners have much work to do to avoid future catastrophes. City officials did not endorse many of the recommendations of the Task Force in 2010. Perhaps they will reconsider their position now?

Chris Mooney at Mother Jones provides more information.