Storm Surges and Climate Warming

The following discussion of the effects of climate warming upon storm surge heights along the Atlantic and Gulf coasts of the United States is modified from the blog of Dr. Jeff Masters (www. wunderground.com).

A storm surge of the magnitude experienced in Hurricane Katrina, which charged into the northern Gulf Coast in 2005, occurred every 20 years since 1923 , according to a storm surge index developed by Aslak Grinsted, of the Centre for Ice and Climate at the Niels Bohr Institute (Copenhaven). The index is produced from a statistical model that links global temperatures to the risk of Katrina-level storm surges. The data used in the modeling come from six tide gauges located along the coast from Texas to New Jersey for the period from 1923 to 2011. The authors  conclude that, because of global warming, Katrina-magnitude storm surge events (see photographs below) have already more than doubled in frequency since the late 19th century. Their modeling found that a global temperature increase of 0.4°C was sufficient to double the odds that storm surges would reach the levels seen in Hurricane Katrina. Since global temperatures have already risen 0.6°C since the late 19th century, “we have already crossed the threshold where more than half of all ‘Katrinas’ are due to global warming,” said Grinsted.

shipisland_surge

Figure 2. High water marks on East Ship Island, Mississippi, after Hurricane Katrina in 2005. Katrina brought the highest storm surge ever recorded on the U.S. coast, 27.8′ at Pass Christian, MS. Left image: Bark stripped off a tree by storm surge (note the 25 ft (7.65 m) long survey rod for scale). Right: Massive beach and over wash erosion damaged and snapped pine trees along the beach. Arrows show the high water mark left by the storm surge. Image credit: Fritz et al., 2007, “Hurricane Katrina storm surge distribution and field observations on the Mississippi Barrier Islands” (PDF File), Estuarine, Coastal, and Shelf Science (2007), doi:10.1016/j.ecss.2007.03.015.

Projecting into the future, the model suggests that with a  1°C  rise in global average temperature, Katrina-level storm surge events would become two to seven times more frequent. Since sea level probably will continue rising due to global warming, these future storm surges will be piled onto an elevated ocean surface, increasing their potential for greater damage than in the past. Although future statistical  relationships between surge height and temperature  might possibly change as the climate continues to warm, Masters says that the surge heights projected by Grinsted and colleagues are quite possible. Coastal planners should therefore take the projected surge heights seriously, particularly considering that human populations are expected to increase in vulnerable coastal areas. Increased investment in  improved shoreline protection in the coming decades is one cost that the U. S. and other coastal nations would face in response to higher and therefore more penetrating storm surges. References consulted include:

Grinsted, A., J. C. Moore, and S. Jevrejeva, 2012, “A homogeneous record of Atlantic hurricane surge threat since 1923,”PNAS 2012, doi:10.1073/pnas.1209542109;  Grinsted, A., J. C. Moore, and S. Jevrejeva, 2012, “Projected Atlantic hurricane surge threat from rising temperatures” PNAS March 18, 2013 201209980,doi: 10.1073/pnas.120998011;  stateofthe coast.NOAA.gov; wunderground.com/blog/JeffMasters/comment.html?entrynum=2373

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