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by John Englander
President, International Sea Level Institute
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Historic buildings in coastal regions are one of the prime battlegrounds in the race against rising sea level. Our preserved buildings are often fragile and always priceless. Often they have lasted centuries due to devoted care and restoration. With the latest evidence about rising sea level accelerating, this is the time to plan so that they might survive this century.
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Architects and planners know that a good plan starts with the right design criteria. that means understanding what could occur as sea level gets higher. It is more complicated than most would imagine.
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Sea level rise (SLR) is often confused with flooding from storms, extreme high tides, and heavy rainfall. As disastrous as they may be, those are all short-lived events, allowing the water to recede and recovery to begin. Rising sea is essentially a permanent rise in the base ocean height. It will not go down for centuries and will elevate all those short-term flood events ever higher.
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Projections for SLR keep changing and are getting higher as the evidence of glacier collapse in Greenland and Antarctica accumulates. In 2012 the most recent US Government review said that sea level could be as much as 6.6 feet above present by the year 2100—though even that was not an extreme upper limit. See here for the full explanation, with a list of references. With 2016 and each of the last few years , the signals of faster ice melt and higher sea level are now in front of us.
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 Traditionally we paid little attention to sea level changes because the rate was rather slow. As a global average sea level rose about 8 inches (20 cm) in the last century. It has not changed significantly in the last few millennia. In geologic time, sea level moves hundreds of feet up and down, by nature on a cycle time of roughly a hundred thousand years. It’s part of the pattern we know as the ice ages. The last ice age peaked 20,000 years ago and sea level was almost 400 feet lower. One hundred thousand years earlier sea level reached an amazing 25 feet higher than . It is headed back there. To view and download a simple colored graphic of 400,000 years of sea level change, with global temperature and carbon dioxide levels go here. Now things are happening much faster, making it more of a challenge to plan responsibly. The core issue is the ice sheets and glaciers on Greenland and Antarctica.
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When I advise groups such as architects in vulnerable Florida, to the Port Commissioners in San Francisco, or the City of Annapolis, I recommend that they plan for three feet (roughly a meter) of SLR as soon as possible. we can forestall that amount of increase to the end of the century. But even if it happens by mid-century, we can be prepared. It is worth recognizing that AIA Florida recently adopted just such a visionary policy position.
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In some it may be possible and even desirable to plan for a higher level such as two or three meters, rather than doing it in stages over the century. It is also important to consider regional and local variations that can be huge. Areas like Hampton Roads and New Orleans have dramatically greater SLR than the global average. In New Orleans, the most extreme situation in the U.S., the rise has been over 45 inches since 1880 due to the land in that area subsiding.
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In deciding how to protect historic structures, an assessment needs to be done for each specific location that takes into account the regional and local geologic factors such as subsidence, or porous bedrock that will determine whether seawalls and levees can shield the structure from water. Rising sea level combining with storms and extreme presents different problems in different places. What works in Manhattan will not work in Miami.
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Unlike the damage from storm waves that is somewhat limited to the coastline, SLR extends through marshes and wetlands and can push hundreds of miles up tidal rivers greatly expanding the vulnerability zone. For example, Sacramento and Hartford Connecticut are located on tidal rivers, are extremely vulnerable to SLR even though they are quite far from the coast.
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Rising sea level is often confused with the larger issue of climate change, with sustainability, , and reduction of greenhouse . While all of those are important and have some relevance, they must not confuse or distract your focus to design for rising sea level.
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The oceans have already been warmed almost a degree and a half F. Even if the world went 100% solar tomorrow, we are still going to get SLR as the ice sheets on Greenland and Antarctica continue to melt. It is now locked in for centuries. Reducing greenhouse gas emissions like carbon dioxide through better energy policies is very important at the global level in the long term. At a local level, reducing GHG emissions will not have any real effect on SLR, even over the next few decades. They are essentially separate issues.
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Ultimately you may come down to tough choices about protecting historic structures and even consider elevating or even relocating them. It is important to evaluate the options in economic terms over a fairly long future. Short term planning can result in cost in the long term. Fortunately today we do have tools to do very sophisticated planning and evaluation of options.
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Now is the time to plan, protect, and preserve. If it is done well, it can reap rewards for centuries.
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John Englander is a consultant, speaker, and author of the authoritative book “High Tide on Main Street: Rising Sea Level and the Coming Coastal Crisis” (The Science Bookshelf, 2nd Edition 2013) in print and for Kindle. He is president of the Rising Seas Group, a firm that helps communities, companies and organizations understand, assess risks, and plan for adaptation. He can be reached at englander@risingseasgroup.com
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