Since Jean-Baptiste Le Moyne de Bienville founded the City of New Orleans in 1718, the water that surrounds the city has defined its very existence. With changes brought on by global warming that water also has the very real possibility of destroying it over the next 100 years.
Climate change is a reality, and one of the most damaging effects of it in the United States, especially for coastal cities like New Orleans, is sea-level rise. NASA data indicates that since 1993 global sea levels have risen at a rate of 3.16mm/yr., or about 2.4 inches in the last 20 years. According to a new report, Louisiana should anticipate a 3.3-foot rise by the year 2100.
Sea level rise is not the only problem
New Orleans has another problem in addition to sea-level rise; a process called subsidence, or in layman's terms, it’s sinking into the ground. USGS data shows that in the next 100 years New Orleans will sink approximately 50 centimeters or 19 inches. Areas of New Orleans that are presently 1.5 to 3 meters below sea level will be 2.5 to 4 meters below sea level by 2100.
Dr. Mark Kulp, professor of geology at the University of New Orleans, said, “Subsidence is something that affects deltas on a global basis. The Nile delta has subsidence problems, the Mekong Delta, Yangtze delta, the list goes on and on and on.” Kulp also explained that is somewhat unique because we have a major metropolitan city in the middle of the high subsidence zone.
Planning for the eventual rise in the waters is further complicated by the fact that the increase isn’t uniform. For instance, at Grand Isle, La., about 50 miles south of New Orleans, NOAA data shows sea levels will rise at a rate of 9.24mm/yr. and not the much lower 3.16mm/yr. global rate.
The temperature is rising
The temperature of the planet is also increasing, but the increase is not uniform across the globe. As the earth warms, water expands. The warmer the water, the more sea-level rise there is local to that area.
From 1880 to 2010 the mean global surface temperature relative to the average temperature has been trending upward. By 2010 both the annual mean and the 5- year average were at a +0.6 Celsius, meaning the earth, as a whole, is a half a degree warmer. In 2012, global surface temperatures were the ninth warmest on record.
More and stronger hurricanes
Warmer waters mean more frequent and more destructive hurricanes. Dr. Kulp said, “Some of the predictions that are associated with climatic change are that there will be an increase in the, essentially the destructive intensity of hurricanes, and possibly even [the] frequency of hurricanes.“
The primary hurricane protection tool in the New Orleans area is a vast and complex levee protection system. Levee heights are often determined using historical storm surge data, and then the Army Corps of Engineers tries to factor in the probability that one storm in 100 years would be able to top that levee.
Are levees enough
New Orleans is attempting to create a levee system that will protect it from a 500- year storm. According to Denise Reed, Ph.D., Chief Scientist for the Water Institute of the Gulf, the subsidence issue may complicate that. Reed said, “The city is surrounded by levees. Over time, because of subsidence, the elevation of those levees gets lower relative to the water level.” She continued, “If we want to keep the same level of protection associated with those levee systems, we have to keep putting dirt on them.” Dr. Reed makes clear that with sea-level rise this will be a continual process for the city.
According to the State of Louisiana damages from flooding due to storm surge and rain events average 2.4 billion dollars annually. If significant improvements are not made to reverse coastal erosion and improve hurricane protection systems, by 2061 damages could be as high as 23.4 billion dollars annually.