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When it comes to SLR, conservatism is (unrealistic) optimism

November 26th, 2012 · 8 Comments

For some reason (hint: Sandy), The New York Times has become a powerful voice Planet of the Apesin the traditional U.S. media scene when it comes to climate change issues. Worthwhile opinion pieces, over this past weekend, included Rising Seas, Vanishing Coastlines and Is this the end? Associated with these articles is a powerful graphical tool that shows, for key American coastal areas, the impact of sea-level rise.  Entitled What could disappear, this interactive tool always us to assess rapidly the impact of varying amounts of sea-level rise in the Baltimore, Boston, Charleston, Houston, Jacksonsville, Los Angeles, Long Island, Mobile, New Jersey, New Orleans, New York, … areas.  The list is daunting to consider.  This tool allows one to peg the sea level rise anywhere between 0 and 25 feet.

Looking at what this map projects for what would happen in 100 to 300 years, a 5 foot sea-level rise, it is rather sobering to see how much land — how much high-value urban infrastructure — ‘disappears’ beneath the waves.  Take a look at, for example, New Orleans to the right.  With a five-foot rise, New Orleans will be “88% flooded”.  That’s New Orleans, of course we know that it as risk.  Looking elsewhere, Atlantic City will be 62% flooded, Huntington Beach (CA) will be 27% flooded, Galveston (TX) 68% flooded, Cambridge (MA) will be 26% flooded, and so on. That, of course, is only a 5 foot rise.  Want a truly shocking image, look to the future of America’s coastal areas in face of a 25 foot rise which is “the potential level in coming centuries, based on historical climate data.” Taking the moment to ‘play’ with What could disappear provides a depressing projection on the challenges ahead when it comes to managing coastal areas in the face of climate-change driven sea-level rise.

That ‘depression’, however, derives from what is actually a rather conservative projection that — due to its conservatism — actually represents a rather optimistic scenario.

What are some (potential) issues with these representations?

  1. A five-foot rise is listed as the “probable level in 100-300 years”. If, as projected from current business-as-usual practices, there is a seven degree (or so) increase in global temperatures by the end of the century, a five-foot rise seems likely by 2100 (or within the 100 year window).  The worst-case scenarios might have a 12 degree rise by 2200 which seems likely to be accompanied by a sea-level rise much more significant than 5 feet, perhaps approaching the 12 feet that the New York Times projects for 2300 (in a scenario where nations do only “moderate pollution cuts”).
  2. This does not seem to include many complexities, such as land subsidence in, for example, the Chesapeake Bay area that are interacting with rising seas to hasten the impact on land areas.
  3. It seems to apply solely the global average sea-level rise around land levels rather than accounting for regional variations in sea-level rise. This matters, significantly, for the New York Times subscriber base as the East Coast of the United States is seeing and will see a larger sea-level rise than that global average.
  4. This does not address ‘underground’ issues, such as saltwater intrusion on acquifers (which create serious problems for Eastern Shore agriculture well before land goes under the ocean) or the threat to infrastructure like sewer systems in port areas.
  5. There isn’t any representation of how storm surge impacts change with rising seas (re Norfolk, VA, area). These graphics demonstrate what will be covered but not necessarily what will become exposed to storm surges.  (The NYT OPED cited above, Rising Seas, Vanishing Coastlines, discusses this very sort of issue.)
  6. And …

Greg Laden provided me an example of another ‘and’.  What could disappear shows us what gets covered by rising seas but doesn’t deal with how rising seas will erode land that theoretically would remain above the new sea level.  When it comes to transgression, consider the Boston map.  From about Cambridge north, the inundation depicted is pretty close to what will likely happen given the because the land has hard hard basement rock near the surface. South of Boston, however, the substrate is glacial till at depth. Rising seas almost certainly would erode away at this and thus rising sea levels would likely mean fewer and far smaller islands than shown with these interactive maps. The many little islands shown as still sticking above the sea would all be sea mounts except in the occasional spot where a core of bedrock would be still visible, to produce islands much smaller than shown.  Long Island is an even more striking example. With the 25 foot sea level rise, the Long Island map shows 21% flooded (to the right).  However, the only thing that would be left of Long Island is its rocky core.  The moraine would eventually turn into cobbles and rocks in situ and mostly be shifted to sea as a sand sheet.   The highest elevations on Long Island are ca 120 meters as based on the topo map. The thickness of quaternary sediments in those areas is between 90 and 105 meters in those areas.  Those small patches would be islands if the ocean had its way with Long Island. Long Island will, in a few thousand years, become a large clam flat surrounded by some nice fishing grounds without sea level rise. With sea level rise, currently unaffected by the sea land faces would become exposed to strand line erosion. Looking back at the topo map, most of the area that is about 20-40 meters above sea level (blue to dark green would be eroded very quickly with just a few meters of sea level rise.

There is another issue here — the timing challenge and getting attention from citizens, organizations, politicians.  In an environment where ‘long term strategic planning’, especially for the business community, rarely goes past 5-10 years, speaking about impacts three centuries from now has a hard time eliciting a yawn from most.  With an economics profession ready to apply ‘discount rates’, a Starbucks coffee (okay, a Starbucks specialty drink) today might have a greater ‘net present value’ than a 25 foot sea level rise in the year 2500.  The reality is, as per the increased impact (reach) of Hurricane Sandy’s storm surge and the regular full moon high tide floods in Miami, we are already seeing real impacts from climate-change driven sea-level rise and those impacts will continue to grow — our societal choice is how bad we are willing to allow these impacts to become because we value that specialty drink today more than climate impacts tomorrow.

The New York Times‘ increased focus on climate change issues, sadly sparked by Hurricane Sandy’s damage to the New York area, could prove a valued contribution to fostering a better national discussion about and, hopefully, more serious national action when it comes to climate change issues.  As part of climate change impacts and risks, What could disappear is a useful tool for understanding sea-level rise.  When using it, however, we should remember that its conservative representation is almost certainly an optimistic look at what will happen in coming decades and centuries.

Tags: climate change

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