Sunday, August 24, 2014

A Tale of Two Cities:  Miami, New York and Life on the Edge

Retreating  (Credit: Cassidy Robison, an artist and student in the Department of Art & Art History, University of Colorado Boulder) Click to enlarge.
Walking along the waterfront in Fort Lauderdale and admiring the 60-foot yachts docked alongside impressive homes, it's hard to imagine that this city could suffer the same financial fate as Detroit.  But it is almost as hard to imagine how they will avoid a similar crisis given the sea level rise predicted by scientists.

The Miami-Fort Lauderdale area, with 5.6 million people, is "ground zero" in the battle against the rising seas.  Perhaps nowhere else in America are the odds lined up so heavily against a region.  With a relatively flat, low-lying landscape, and a porous limestone base that precludes levees, the options for this city do not look good.

Subway under water  (Credit: Cassidy Robison, an artist and student in the Department of Art & Art History, University of Colorado Boulder) Click to enlarge.
A thousand miles north-east lies New York -- another city very vulnerable to sea level rise.  But after the wake-up call of Superstorm Sandy, Michael Bloomberg, then the mayor of New York City announced "We cannot, and will not, abandon our waterfront" and launched a $20 billion program to protect the city against the rising seas -- at least for a little while.  So why can't Miami apply the same formula as New York City, and go back to relaxing on the beach?  And what is this concern about sea level rise in the first place? 

Most of us have heard of climate change or global warming, but what we may not realize is that about 90 percent of the heat being trapped by increasing greenhouse gases is going into the oceans, not the air.  And as the oceans become warmer, they expand -- causing the sea level to rise.  Sea level for most of the 20th century rose at the rate of about 6 inches per century.  In recent years this rate has approximately doubled to a rate of just over 12 inches per century.  Scientists predict that the pace will increase even more as the large ice sheets of Antarctica and Greenland begin shedding more ice to the ocean. Just how fast sea level will rise over the coming decades is undetermined at this point, but scientists agree on two points:  the direction is up and the pace will increase.

But what about the costs to the nation from the encroaching seas?  They, too, seem likely to rise.  Precise predictions of how high sea level will rise in the coming decades are difficult to make, and as a result forecasts vary significantly.  This makes it tough for urban planners who need to know what to prepare for and when those plans need to be in place.

To get a prediction his city planners could use, Bloomberg gathered a group of scientists together in 2008 to predict the local sea level rise for the coming years.  Their estimates had a mid-range prediction of 11 - 24 inches by the 2050s.  They did not predict beyond the 2050s, a key issue they plan to address in their next report and that we will return to later. 

New York City was in the process of planning for sea level rise when Sandy hit in October 2012.  If the city did not have reason to prepare for sea level rise before Sandy, it sure did afterwards.  Sandy, a "1-in-70 year storm" with its 9-foot storm surge flooded 17 percent of the city, impacting 443,000 people and 88,700 buildings.  It caused $19 billion in damage to the city alone.  Swiss RE, a re-insurance company, estimated that if nothing is done to protect against sea level rise, a similar 1-in-70 year storm would cause $90 billion in damage to the city by the 2050s.

During tropical storms and nor'easters, storm surges pose a bigger threat than the actual sea level rise.  Storm surges are caused primarily by an on-shore wind literally pushing the water towards shore.  Combined with large waves from the storm, the storm surge can be the most damaging part of the storm.

A Tale of Two Cities:  Miami, New York and Life on the Edge

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