Louisiana’s compounding coastal threats

By Alisha A. Renfro, Ph.D., Staff Scientist, National Wildlife Federation

Worldwide, rising global temperature is a threat to coastal communities in the form of rising sea levels and stronger hurricanes. Last week, the Louisiana State Museum in New Orleans hosted a presentation by Virginia Burkett, Ph.D., Chief Scientist for Global Climate and Land Use Change at the United States Geological Survey. In Dr. Burkett’s presentation, “Climate Change and Sea Level Rise: Implications for New Orleans,” she discussed the science of climate change and the threats sea level rise present to the vulnerable low-lying landscape and communities of coastal Louisiana. Louisiana’s 2012 Coastal Master Plan acknowledges these threats and outlines a 50-year plan for protection and restoration that takes into account subsidence, sea level rise and increased storm frequency and intensity.

Long Term Relative Sea Level Trends for the United States. Source: NOAA.

Global sea level rise is a consequence of water influx from melting glaciers and ice sheets and the expansion of ocean water as it is heated. During the 20th century, global sea level rose approximately eight inches, but satellite data indicates that the annual rate of sea level rise has almost doubled over the last 20 years. As the different processes that affect melting of large ice sheets are still the subject of intense scientific study, the range of predicted sea level rise in this century ranges from 0.6 to 6.6 feet, but  the most likely range of sea level rise is between one and four feet.

While the predicted rate of global sea level rise is enough to cause concern for many coastal regions, in Louisiana, the threat is intensified as not only is sea level rising, but the land is also sinking. Subsidence can occur due to natural geological processes, such as dewatering and compaction of deposited river sediments over time, but it can also be increased by human actions, such as groundwater withdrawal and oil and gas extraction. Subsidence rates across Louisiana’s coast vary, but in many areas, the rate of subsidence far exceeds the global rate of sea level rise. The combination of global sea level rise and local subsidence means that the local sea level will rise sooner and higher in Louisiana than in most other places in the world.

Sea Level Trends. Source: NOAA

At the conclusion of her talk, Dr. Burkett had a few recommendations for actions we here in Louisiana can take to adapt to sea level rise and increase the resiliency of our coastal communities and coastline. For coastal communities, elevating and flood-proofing infrastructure are important steps for adapting to the increased threat of inundation from sea level rise and hurricanes, but in some cases, retreat from low-lying coastal areas may be necessary.

We can better manage our coast by factoring our understanding of the natural processes and trends and by getting sediment from the Mississippi River into the wetlands. As one of the most vulnerable areas to sea level rise in the United States, coastal Louisiana will serve as the testing ground for scientific innovation and policy that will likely shape the response of coastal communities throughout the country to the threats of climate change and sea level rise.