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.

A table labeled 'States with the most to lose from coastal habitat.' The states are Florida, New York, California, and New Jersey. Florida and New York both have around 335,000 thousand people protected by coastal habitats whereas the other states have around 100,000. Additionally, Florida and New York both stand to lose $80 billion in protected property, whereas the latter states have about $23 billion to lose.

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.

A map of the distribution of coral reefs and coastal forests in the United States, the #1 source of coastline protection. Coastal forests are highly prevalent in the east and southeast. Coral reefs are highly prevalent near the tip of Florida and in Hawaii.
A map showing the distribution of high dunes, oyster reefs, and emergent wetlands in the US, the #2 source of coastline protection. Emergent wetlands are prevalent throughout the US. Oyster reefs can be found in the east, and high dunes in the southeast and along the western coast.
A map of the distribution of low dunes in the United States, the third most important source of coastline protection. They're most found along the east and gulf coasts.A map of the distribution of seagrass beds, kelp forests, and other intertidal aquatic vegetation found throughout the United States. Seagrass beds are prevalent throughout most of the US coastlines. Kelp forests are mostly found on the west coast.