Sea-Level Rise in the Coming Years: Impacts to Dynamic Coasts

Coastal systems by their nature are dynamic and exhibit non-linear behavior. Recent climate change assessments conclude that increase in global temperature is unequivocal; and, that warming and wide-spread environmental change result primarily from increase in greenhouse gas emissions. The CCSP SAP 4.1(2009) report concludes that a consequence of climate warming will be that coastal systems are very likely to become even more dynamic and less predictable. One of the most significant climate-change effects is sea-level rise (SLR).  Direct SLR effects include: erosion, more frequent tidal and storm-surge flooding, inundation of low areas, saltwater intrusion into aquifers, wetland loss, and risk to urban infrastructure.    

Deltas world-wide are particularly vulnerable due to their low relief and high subsidence rates of ~12 mm/yr. Global SLR adds to subsidence effects and SLR rates are shown to be accelerating (~3 mm/yr). Many deltas too are impacted by sediment starvation due to dam impoundments and by effects of flood-control structures. Sea-level rise rates for much of the mid-Atlantic region are higher than global averages due to land subsidence from continuing isostatic adjustment from ice sheet loading and unloading during the last Pleistocene ice advance. For example, the average global rate of rise has been ~ 1.7 mm/yr for the 20^th C, but the trends observed from gauges range from 2 mm/yr rise in Maine to 4-6 mm/yr rise for coastal Delaware to Virginia, the region of maximum isostatic subsidence. Maximum rates of ~ 10 cm/yr occur along the Louisiana delta plain coast due to subsidence from sediment compaction.        

IPCC (2007), suggests that global sea level for this century will rise up to 59 cm.  More recent modeling studies, however, suggest that rates may be significantly higher in decades ahead due to processes that appear to be strong, but little understood. These studies suggest that global SLR could be ~ 1 m or more during this century; however, continued accelerated melting in Greenland and West Antarctica could lead to 4 m or more rise over the next several hundred years.

Accelerated sea-level rise will have significant impacts on coastal systems and societies world-wide.  It is uncertain, however, whether current techniques used to predict coastal change can provide reliable long-term predictions at scales optimal for local planning and decision making. With substantial acceleration of SLR, traditional coastal management and engineering practices may not be economically or environmentally sustainable.