How much sea level rise could these cities cope with before the cost of defending them becomes prohibitive?
Being a climate scientist who does a lot of work in London this is a question I’ve been asked several times, especially by organisations with a vested interest in remaining in London (city institutions, insurance industry etc).
London is relatively easy to defend as it’s not on the coast (it’s on the tidal section of the Thames) and it already has the Thames Barrier that can be raised to cut it off from the sea. This was installed in the 1980’s and was expected to last for at least 100 years. Rising sea-levels mean it’s likely to need replacing by the 2030’s.
Plans are already being drawn up for the construction of an even larger barrier further down the Thames, this is part of the Thames Estuary 2100 review.
When the present Thames Barrier was constructed it wasn’t envisaged that sea-levels would rise quite so much. As a result it’s now closed ten times as a frequently as it used to be (11 times in it’s first ten years, 107 times in the last ten years).
These closures have prevented massive flooding in London and the Barrier has paid for itself many times over.
In 1953 a tidal surge in the North Sea claimed the lives of nearly 2,000 people. In December 2013 there was an even higher tidal surge but with the flood defences in place not a single life was lost and hardly anyone even needed to evacuate from their homes.
Flood defences definitely work. The UK has just had it’s wettest winter on record but less than 10,000 properties were flooded. Without flood defences more than a million homes would have been flooded.
Whilst London can be protected for at least 200 years with relative ease, the same can’t be said for coastal cities such as New York and Miami. New Orleans is even harder to protect as much of it is below sea-level.
To protect a coastal city would require the construction of immense coastal defences, these would have to form an impenetrable wall that could withstand the force of the sea stretching some considerable distance beyond the city limits.
Hurricane Sandy (TS Sandy when it hit New York) brought tidal surges of 7 metres. To protect the city against such event sin the future would mean constructing defences right around the coast line, because of the shape of New York and the fact that some of it is on islands means that these defences would be of great length. They would also carve through areas of prime real estate and many waterfront buildings would need to be demolished.
Massive infrastructure changes would be required (gas, water, electric, phone, sewerage, Metro, roads, rail would need rerouting), thousands would need rehousing.
Such a scheme could be undertaken and the US certainly has the resources to do so, whether public opinion would permit such a thing is a different matter.
After adjusting for inflation, nine of the costliest Atlantic storms in history have occurred in the last 10 years (respectively – Katrina, Sandy, Ike, Wilma, Ivan, Irene, Charlie, Rita and Frances. Andrew is the exception, it occurred in 1992 and ranks 5th in terms of cost). Losses from Katrina were $125 billion, from Sandy they were $68 billion.
Indications are that unusual storms such as Sandy will become more frequent, although hurricane numbers as a whole may well decline. The questions is – how much do you spend on defences and where?
Protecting NYC could cost anywhere from $50 billion to $400 billion, depending on the scope and extent of any works undertaken. This investment could pay off within months, or it may never pay for itself. Other coastal cities face the same dilemma.
It’s feasible that we can protect our cities against most anything the seas and oceans can throw at us for at least another century, even allowing for the worst case scenario when it comes to sea-level rises.
Theoretically we could enclose our cities within barriers so high that they could hold back the oceans even if all the ice in the world were to melt (sea-level would rise by 80.32 metres). It probably wouldn’t be cost effective, but it could be done.
There’s no way of knowing what storms will hit in the future, where they’ll hit and how much damage and financial loss will be incurred. Sea defences will always be something of an insurance policy and we’d hope never to have to need them but it’s good to have just in case.
To answer your specific question about when it becomes prohibitively expensive to defend cities… much of the cost is incurred in land purchase, infrastructure and construction of the foundations. Thus, it doesn’t cost much more to build a 10m high defence than it does to build a 5m high defence. As such, the question becomes – is it worth defending in the first instance? The answer to this is something the City Planners and citizens will need to decide and the taxpayers will have to fund.
They can either try to keep the water away like holland has or live with it like venice. Either way it runs into billions and given the US appetite for taxes and public works I think an attitude adjusment will be needed.
It's more likely for ny than new orleans.
Best to ask the people in the Netherlands
Weird question. Try defining "uneconomic". Or give up and ask something less weird.
It is a good question, however it is not really about sea level, as sea level rise over the last century has only been about 8 inches, and as storm surges can be up to 7 meters high an additional 8 inches hardly makes a lot of difference.
Protection against storm surges is definitely a good idea, and many should be carried out now, the huge damage and loss of life that was incurred in New Orleons could have been largely avoided, it was known for a long time that there was a weakness with their storm defences, but there was a reluctance to spend big sums of money to put it right, but in hindsight it would've been money well spent.
How about Miami? How about New Orleans?
How much sea level rise could these cities cope with before the cost of defending them becomes prohibitive?
