According to its most recent report, the Intergovernmental Panel on Climate Change estimates that even with aggressive emissions reductions, global average sea levels will rise between one and two feet by the century's end. For coastal communities in the United States, storm surges—such as the record 13.9-foot surge that inundated lower Manhattan when "superstorm" Sandy made landfall in 2012—could become commonplace. The conventional coastal defense approach of "hardening" shorelines, while appropriate in some situations, has its drawbacks: Seawalls and similar man-made structures are expensive to build and maintain, detract from aesthetic and recreational value, and may contribute to environmental degradation.
A savvier strategy, proposed by Stanford scientists working with the Natural Capital Project, is to invest in conservation and restoration of coastal habitats that serve as natural barriers and buffers—particularly in regions where they shield vulnerable populations, high-value property or both. The research team identified and mapped key habitats—coral reefs, coastal forests, emergent marsh, seagrass beds, kelp forests, intertidal aquatic vegetation, oyster reefs and sand dunes—that provide varying degrees of protection against flooding and erosion caused by sea level rise and storm surges.
"If we lose these defenses, we will either have to have massive investments in engineered defenses or risk greater damage to millions of people and billions in property," says the study's lead author, Katie Arkema, a postdoc at Stanford's Woods Institute for the Environment.
A collaboration of the Woods Institute, the University of Minnesota's Institute on the Environment, the Nature Conservancy and the World Wildlife Fund, the Natural Capital Project aims to quantify nature's benefits to society and incorporate its value into policy decisions. The analysis carried out by Arkema and her NCP colleagues is the first to synthesize coastal hazard and climate change models with ecological and demographic data. The resulting interactive map illustrates—on both a national and local scale—the areas where conservation or restoration efforts are most critical.
All told, these habitats currently cover more than two-thirds of the nation's coastline and reduce by half the proportion of people and property exposed to the highest hazard risk. Florida tops the list of states that would feel the greatest impact of the loss of these habitats, followed by New York, California and New Jersey. However, as the study's authors note, "focusing solely on property value may cause decision-makers to overlook ecosystems that provide disproportionate protection to vulnerable populations." The devastation of Hurricane Katrina, for example, was as much a function of socioeconomic factors that made it difficult for individuals to avoid the storm and cope with its aftermath as it was of New Orleans's physical exposure.
HELPFUL HABITATS: Ecosystems that shield shorelines by, for example, dissipating wave energy or anchoring sediments were ranked according to the amount of protection they afford.