Maryland Reassesses Local Sea Level Rise: More of Us Are Going to Get Wet

Maryland Reassesses Local Sea Level Rise: More of Us Are Going to Get Wet

June 26, 2013 19:14
by J. Wylie Donald

We have looked at Delaware's perspective on rising sea levels several times in recent months.  Now it is Maryland's turn.  Today a panel of experts led by the University of Maryland Center for Environmental Science issued an update to Maryland's 2008 assessment:   Updating Maryland's Sea Level Rise Projections.  The conclusion is disturbing.  In the passage of just five years, the anticipated sea level rise in the mid-Atlantic states now exceeds the previous high range.

The origin of the report is  Governor Martin O’Malley’s December 28, 2012 Executive Order on Climate Change and “Coast Smart” Construction, which called for updated sea level rise projections based on "an assessment of the latest climate change science and federal guidance."  Maryland has the fourth longest tidal coastline in the continental United States and loses 580 acres every year  to shore erosion.  Id. "Thirteen Chesapeake Bay islands once mapped on nautical charts have been lost." Id.  The State has 450 facilities and 400 miles of roads within areas likely to be impacted within the next 100 years.  Id.  Hence its interest in rising seas.

And the seas are rising, faster than they have before.  More and better data confirm this. 

(1) the 20th century experienced the highest rate of sea-level rise in the last 2,000 years;
(2) global mean sea level (GMSL) rose at an average rate of 1.7 mm yr-1 during the 20th century based on tide gauge records and an average of 3.2 mm yr-1 from 1993 to the present based on satellite measurements;
(3) rates of melting of the Greenland and West Antarctic ice sheets accelerated; and
(4) sea level is likely to rise more than estimated by the IPCC 2007 assessment.

Update at 3.  With respect to the mid-Atlantic region, "relative sea-level rise of 7-8 mm yr-1 has been measured at Maryland tide gauges between 2002 and 2011", although scientists consider this period too short to identify a trend.  Update at 7.

Sea levels are eminently local attributes and affected by much more than the flows from the melting of arctic ice and the warming of the oceans.  The researchers considered, among other things

  • the amount of water being stored behind dams or pumped out of groundwater aquifers (expected to be a net addition over the next century);
  • the weakening gravitational effect of melting arctic ice masses that "counter-intuitively result[] in sea-level decline in nearby polar regions and sea-level increase in tropical regions";
  • glacial isostatic adjustment, which is the rebound of land once weighed down by the glaciers, as well as the subsidence of the "forebulge" of unglaciated lands at the front of the glacier;
  • the slowing of the Gulf Stream, which has the effect of causing coastal waters to rise; and
  • the increase in tidal ranges and storm surges, which are amplified by rising sea levels in an enclosed body of water like Chesapeake Bay.

In case all of that was a little complex, the researchers obligingly "put it all together."  The best estimate of sea level rise in Maryland by 2050 is 1.4 feet, with a range of 0.9 to 2.1 feet; by 2100 it is 3.7 feet with a range of 2.1 to 5.7 feet.  Update at 15.  To put this in perspective, the best estimates in the 2008 Maryland Climate Action Plan (p 53) were by mid-century a range of 0.6 feet to 1.3 feet or by 2100 2.7 to 3.4 feet.   Now the best estimate exceeds the high range of only five years ago.

As Governor O'Malley put it in his executive order, "The State of Maryland must take action now to ensure that State infrastructure investments in vulnerable coastal areas are "Coast Smart" - fiscally wise and structurally sound."  We couldn't agree more.

In closing, we don't often look far out into the future in this blog because its intended focus is the practical here-and-now impacts of climate change on the practice of law.  But the Update offered a sobering perspective on the unshakeable legacy our action or inaction today leaves to our children and grandchildren:

differences in 21st century emissions trajectories begin to have significant consequences for the rate of sea-level rise toward the end of this century and result in even greater differences during the next. In other words, steps taken over the next 30 years to control greenhouse gas emissions and stabilize global temperatures during this century will largely determine how great the sea-level rise challenge is for coastal residents in subsequent centuries. There is not much they could do then to slow sea-level rise because of the inertia of ocean warming and polar ice sheet loss.  Update at 11.

Regulation | Rising Sea Levels

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