Hurricane Harvey and the impact of sea level changes

Guest essay by Philip Lloyd

Hurricane Harvey broke the 12-year pause in Major tropical cyclones making landfall on the continental US. Inevitably, believers in Catastrophic Anthropogenic Global Warming [CAGW] had a celebration. They had correctly predicted climatic disaster. It mattered not that there had been earlier, stronger storms. Harvey was clearly the result of humans sinfully burning fossil fuels.

One of the problems with CAGW is the mistaken belief in an unchanged and unchangeable globe. Yet we know that on a macro scale, continents wander over the face of the earth and occasionally collide, throwing up huge mountain ranges. Around the Pacific, plates slide over the ocean floor, creating devastating earthquakes and chains of volcanoes. Glaciers grind away the slopes of high peaks, forming characteristic valleys. Rivers meander across the plains, shedding ox-bow lakes as they carve new passages. Nowhere does stasis rule.

Fixation is a poor guide to causation. Something struck me as I viewed aerial pictures of the floods as they poured off the land. Drainage was far slower than I had expected. Was something happening along the Gulf coast to alter the drainage? Much of it is low-lying. Was the sea-level rise of 2-3mm per year showing some effect?

I went to the tide gauge data (Permanent Service for Mean Sea Level, http://www.psmsl.org/data/obtaining/) There are 35 stations along the Gulf coast, of which 18 had more than 25 years of data and were reasonably complete. One station (Sabine Pass) had data until 1983, when it was moved about 3km and restarted in 1993. The datum evidently moved during the re-siting, but when 310mm was added to the post-1993 data, there was a consistent pattern with a low standard deviation, so an additional “station” using the combined data was used to fill in a wide gap between two other stations.

The location of the tide gauges is shown in Figure 1.

Figure 1. Location of tide gauges (Google Earth). Freeport, to the west of Galveston, is not labeled

The data were downloaded as a .txt file and imported into Excel. Dates for which the data read -99999, indicating a missed reading, were deleted. The remaining data were analyzed using the Regression function in Excel, which yielded the standard deviation of the trend and an F statistic that was much less than 0.001 in every case. Figure 2 shows the data for PSMSL Station 161, Galveston Pier 21, for which there were nearly 1300 monthly readings, 99% complete from 1908 to 2017.

Figure 2. Data for Galveston Pier 21.

The rate of rise was 6.41±0.10(std.dev.)mm per year. Note that the standard deviation is that of the trend, related to the more usual Pearson R by 1/√(n-1), where n is the number of monthly readings. There is a second station 2.8km south, at Galveston Pleasure Pier, PSMSL Station 828. Data is from 1958, but is only 89% complete. The rate of rise was 6.55±0.30mm per year. A T test showed that it was statistically identical to the Pier 21 data, giving high confidence in the reliability of the analysis.

The rate of rise is shown for all stations in Figure 3. In the east, the mean sea level averages the global average 2-3mm/year, which implies that the land is neither rising nor sinking. However, from Grand Isle at the mouth of the Mississippi west to Rockport, the rate of rise of sea level is 6-10mm/year. If the sea level is rising naturally at 2-3mm/year, then the land must be sinking at between 3 and 8mm/year.

Figure 3. Sea level rise at stations along the Gulf coast

Over the course of a century, the mean sea level could approach 1m rise. The impact of this would not be insignificant, and should certainly be taken into account in planning any development in coastal regions. Focus on CAGW is global, and local issues such as abnormal sea-level rise are all too easily blamed on the global problem. All the hot air expended on rising carbon dioxide in the atmosphere will do nothing for a sinking Gulf coastline.