I think they should start doing it now, in the long run it would benefit them greatly. I think until we figure out why they are rising, precautions should be made, to protect the coast line. Its just a matter of time,before it gets out of control. It may or may not get that bad,but its good to take precautions.
The sea gates used in the Netherlands have amply demonstrated themselves to be an excellent, if expensive, method to control sea level changes and protect against disastrous flooding. Given that the eastern seaboard is in grave danger from rising sea levels, major cities that can effectively use sea gates should investigate doing so.
I think detailed studies need to be done on the threat of rising sea waters to New York City and if there is a sufficient evidence that they will pose a threat on New York City in the next decade then I would fully agree with taking measures like building sea gates.
Yes, New York City should build sea gates to protect against rising waters, because if they see a problem coming there is no reason that they should not take steps to prevent it. If New Orleans knew Katrina was coming, they could have taken preventative measures. New York City can see the rising waters coming. They should defend themselves.
I do not believe New York City should build sea gats to protect against rising waters. I believe this is a really dangerous scenario. My impeding the water's flow and building a sea gate there will be a time in the future when these gates will have to hold water out on a daily basis, what happens when they fail and the water all spills into Manhattan at the same time. It would kill everyone in the first floor and below. It would be a catastrophe in the making.