Warming Has Doubled Risk of Katrina-like Storm Surges

Global warming has already doubled the risk of Hurricane Katrina-magnitude storm surges in the U.S., according to a new study published Monday.

The study, which was published in the journal Proceedings of the National Academy of Sciences, estimates that for every 1.8°F increase in global average surface temperatures, there could be a two-fold to seven-fold increase in the risk of Katrina-magnitude surge events.

Views of inundated areas of New Orleans following breaking of the levees surrounding the city as the result of storm surge from Hurricane Katrina (2005).
Credit: NOAA.

The latest climate projections call for the globe to warm by between 3.2°F and 7.2°F by 2100, depending on future greenhouse gas emissions and the precise sensitivity of the climate system to such pollutants.

When Hurricane Katrina struck the shoreline of Mississippi and Louisiana on Aug. 29, 2005, it caused water levels along some parts of the shoreline to rise by 28 feet above the astronomical tide level, flattening communities and contributing to the deaths of more than 2,000. Storm surges — which occur due to hurricanes’ strong winds and low central air pressure — are hurricanes’ greatest killer, a point that was driven home again just last year, when Hurricane Sandy killed at least 72, mainly along the coast of New Jersey and New York.

Technically, Sandy was a post-tropical cyclone at landfall, although its effects were similar to a land-falling hurricane, as it resulted in hurricane-force winds and some of the largest waves ever recorded in New York Harbor.

The new study uses a historical record of storm surge events from six tide gauges located along the U.S. coast, all with data going back to at least 1923. The authors of the study compared the changes in observed surge records to several well-known or theorized influences on tropical cyclones, such as global temperature changes, regional sea surface temperature changes, and sources of natural climate variability such as El Niño and La Niña events.

The study concluded that regional sea surface temperatures and global average surface temperatures best match the tide gauge records.

The study also used the tide gauge data to project changes in the probability of extreme storm surge events. It factored out other influences that could affect the magnitude and damage from storm surges, such as sea level rise, but it also may have captured surge events caused by non-tropical storms, such as Sandy-like hybrid storms or nor’easters.

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