The Insignificance and Inconsistency of Sea Level Rise Measurements

According to the National Aeronautics and Space Administration (NASA), global sea levels have risen 99.8 millimeters—about 4 inches—since 1993 based on measurements from satellite altimeters, or about 3.3 millimeters (mm) per year. Supposedly, a warming climate has led to warming oceans which is melting Arctic sea ice and raising ocean levels. Somehow a 1.6 degree celsius average increase in atmospheric temperature led to 5,000 gigatons, or 5 trillion metric tons, of melted arctic ice.

According to NASA, it is prime evidence of climate change and a major indicator of how fast climate change is happening. Not just that, cities could be directly affected by rising seas, and places like Miami have already started to plan for its repercussions by spending $4 billion on sea walls that could be 20 feet tall and ring the city. New York City is also set to spend $4 billion on sea walls.

That total amount of total sea level rise is small. Not just small in total, but also small compared to the variance of oceans whose height can vary with weather, waves, and tidal changes. And small compared to the accuracy of reported satellite measurements (around +/- .6mm). It also hasn’t affected every coastal area consistently, with some areas showing no noticeable change in sea level whatsoever. The threat of worse storms appears to simply be a remnant of improved storm tracking from satellites in the last few decades.

Changes in regional sea level can come from a wide variety of factors, including storm surges, ocean circulation, and subsidence—the gradual sinking of land from weight, tectonic movements, or anything else.

While NASA lists subsidence as one of a few contributing factors, in places like Miami subsidence has been estimated to be around 1 to 3 mm a year—slightly less than what NASA estimates for average global sea rise.

So from those two effects—global sea level rise and subsidence—Miami should ostensibly see a regional sea level rise between 3 to 6 millimeters a year.

Yet based on measurements of sea level in Miami from the British Oceanographic Data Center’s collection of the Global Sea Level Observing System (GLOSS), the average change is below all of those numbers: about 1.5 mm a year.

Not only is that small, it may not be statistically significant. The distribution of measured levels at the earliest period of measurements in 1982 to 1985 compared to the most recent in 1989 to 1992 showed no significant difference (T-statistic=-1.384, p=.167).

And it wasn’t a consistent rise year over year. Average annual sea levels declined in the years between. What might be a better metric than average sea level is maximum sea level, as that would give a measurement of how high they might need to build a sea wall. But between 1986 and 1990, the maximum sea level was actually lower than prior years.

It’s not just Miami, other areas also show an either negligible or even declining sea level rise based on in situ measurements (rather than by satellite): Charleston, SC, Biscayne Bay, FL, Cape Hatteras, NC, and Crescent City, CA.

GLOSS data from the University of Hawaii’s Sea Level Center shows plenty of other locations where the average rise in sea level below that 3.3 mm per year average or sometimes negative.

Greenland, which one might think would see the largest change in sea level as that is where ice is melting and simultaneously lowering the land mass and adding to ocean volume directly, has actually seen declining sea levels since 1993. Otherwise known as “uplift” or isostatic rebound, it’s where receding glaciers outpace any changes caused by growing sea levels.