I’ve already blogged about the lame treatment of sea level in the new DOE report. It has attracted some attention from those who want to know how the Trump administration is butchering climate science. But — unlike the authors of the DOE report — it seems my readers also want to know what’s really happening to sea level along the coasts of the USA.

If global sea level is accelerting (and it is), then it’s no surprise we see statistically significant acceleration on the east coast and Gulf coast of the U.S., by why not on the west coast?

I tested for recent acceleration at U.S. tide gauge stations by fitting a quadratic to the data since 1970. It’s not the best test, but it’s simple and I think it’s a good one. It raises the question, what is the average acceleration since 1970 of global sea level? I took the tide gauge reconstruction from Frederikse et al. and fit a quadratic to its data since 1970, which estimates the average rate of global sea level acceleration since 1970 to be 0.083 ± 0.024 mm/yr/yr (95% CI).

Then I checked the average rate since 1970, and acceleration since 1970 (and their uncertainty ranges) for each station on the coast of USA48 (the “lower 48 states), and divided them into two categories. The eastern stations are on the Atlantic and Gulf coasts, the western stations are on the Pacific. All the east-coast stations but one show faster-than-global (with statistical signficance) rates of sea level rise since 1970 (the global average rate since 1970 is shown by the dashed line, the error bars give 95% CI ranges for individual stations):

Not only is east-coast sea level rising faster than global, it is accelerating faster than global (again, global acceleration shown by the dashed line, error bars are 95% CI ranges):

As you can see, all the acceleration estimates are positive and all but one “statistically significant.” They are also all above the global level with quite a few significantly so.

The story is very different for west-coast stations. Most show slower-than-global sea level rise, and one even sees sea level fall:

Most but not all show positive acceleration, but it is smaller-than-global and in no case statistically significant:

I notice that for acceleration estimates, the uncertainties tend to be larger than on the east coast (both graphs are on exactly the same scale). All but two include the global rate in their confidence interval. Overall, it seem thay are probably accelerating but not certainly so, and probably at a less-than-global rate.

This drastic difference between the coasts has been known for a while, but I don’t know the reasons. I expect that ocean circulation patterns and their changes are primarily responsible. In fact, I often ponder the idea that slowing of the AMOC is part of the reason that sea level is rising so fast on the east coast.

I further sub-divided USA48 stations into five groups. The Northeast includes Atlantic-coast stations from Cape Hatteras northward. The Southeast Atlantic includes those south of Cape Hatteras. The Gulf coast includes stations in the Gulf of Mexico, Southern California includes the Pacific coast to San Francisco, and the Pacific Northwest is north of San Francisco.

I then aligned all the stations in each region to form a regional average, then I analyzed the regional data since 1900 in order to project future sea level in two ways. First is the climate-denier way: fit a straight line to the past and project forward to the year 2050. I used the data from 1900 to 2020 for this process. Second, I used data from 1970 to 2020 to fit a quadratic curve, and extrapolated that to the year 2050.

Here are the stations in the Gulf Coast region with at least 30 years of data:

Aligning them to form a regional average gives these yearly averages, with blue lines showing the two fits: a straight line from 1900 to 2020, and a parabola from 1970 to 2020. Red lines extend them forward to the year 2050:

There’s quite a difference in the two projections. By the year 2050 the quadratic forecast (which includes acceleration) is more than 288 mm (11.3 inches, almost an entire foot) higher than the linear. Note that sea level in this region has already reached the linear forecast for 2050. The Gulf coast shows the largest difference between the two forecasts.

Next on the list is the Southeast Atlantic; here is the regional yearly average and the two forecasts:

Again, there’s a big difference due to acceleration, some 237 mm (9.4 inches). In this case, we have already exceeded the linear forecast for 2050.

The northeast follows the east-coast pattern. The impact of acceleration by 2050 is still large at 227 mm (9 inches):

Clearly the entire east coast is showing rapid sea level rise (faster than global) and rapid acceleration (fasther than global). People living along the coast have good reason to be alarmed.

Turning to the Pacific coast, let’s start with southern California, where the estimated acceleration is small enough that two forecasts only differ by 56 mm (2.2 inches):

The Pacific Northwest shows even less sea level rise (less than 3 more inches by 2050) and less of it due to acceleration (estimated impact at 2050 only 49mm = 1.9 inches):

Of course all these estimates are imperfect, and of course extrapolating simple models too far into the future is ill-advised. But for the next couple of decades, they give us an excellent idea of what the past suggests we expect in the near future. The message is clear. Both coasts will be impacted by sea level rise, but the east coast is seriously impacted already and the forecast is frightening.

That’s mainly because acceleration in east-coast regions is obvious.

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