By Andy May

We’ve all heard the question. We point out there is no evidence that current climate changes, whether man-made or natural, are dangerous or unusual. Then we are asked, but “What about sea level rise? Isn’t that dangerous?” There are many very good technical arguments why the current rate of sea level rise will not threaten humans, New York City, Miami, or Tuvalu. These are urban legends that spawn from silly IPCC models as explained by Ole Humlum in Chapter 10 of our latest book (Crok & May, 2023). How are these myths dismissed quickly in clear language? This is my best attempt in ~600 words. Let me know how I did.

The current rate of global sea level rise is below the accuracy of our current ability to measure it as discussed in Kip Hansen’s Chapter 5 in Crok & May. Figure 1 shows three respected estimated rates. The sea levels are shown as reported and they have different zero points. The Jevrejeva, et al. estimate in blue is 2 mm/year (± ~0.3), the one below that is the Church and White estimate of 1.7 (± ~0.3) mm/year. These estimates are both from tide gauges, although the Jevrejeva estimate does try and include the satellite data from 1993 to 2009. Due to the overlap of the author’s estimates of uncertainty, the two estimates are statistically equivalent.

The lower estimate, shown in gray, uses all the NASA satellite data since 1993. It shows a rate of 3.3 mm/year (Beckley, Callahan, Hancock, Mitchum, & Ray, 2017). The satellite record is too short to be meaningful, we need at least 60 more years of data before we can derive a meaningful rate from satellites. The satellite data only covers the upward part of a ~60-year cycle or oscillation that began in 1991.

Global mean sea level has been rising for the past 170 years, but the rate is cyclical. The cycle shows up prominently in Figure 1 from about 1930 to 1991 in the Jevrejeva et al. reconstruction. It is also seen, albeit in a more subdued fashion, in the Church and White reconstruction. Thus, any estimate of the rate of rise based on a reconstruction (satellite or tide gauge or combined) that is shorter than 90-120 years is erroneous. Sea level fell during the Little Ice Age until about 1861 when it began to rise.

All the rates (since 1900) are projected to 2100 in the upper left box and show sea level rises between 5 and 10 inches by 2100. These increases are much less than the average daily tidal range of over one meter. Such a small rise in 76 years is unlikely to be noticed. It should be noted here that sea level is not the same in all oceans as one might expect. In Panama, sea level is 20 cm (~8 inches) higher on the Pacific side of the country than on the Atlantic/Caribbean side, this is about the global sea level rise expected between now and 2100. Even more important, the tidal range on the Pacific side is much larger than on the Caribbean side.

Measuring global mean sea level is made extraordinarily difficult by the changes in mean sea level from ocean to ocean and the related changes in the daily tidal range. Jevrejeva points out that tide gauges are confined to continental and island margins and most of them are in the Northern Hemisphere, the tide gauge records don’t all cover the same time period, and they are attached to land that sometimes rises and falls itself. Jevrejeva points out that it is not easy to combine the various records into a single global sea level curve.

In a like fashion, any estimate of acceleration in the rate with any of this data, or any combination of it, is little more than a guess. Polynomial fits to all these series can show some acceleration, but the fit to the polynomials is statistically no different than a linear fit to the same data.

As many of my regular readers know, I often throw ideas out there for comment. I want to know what the best arguments against my ideas are. Or did I miss a better argument? So positive or negative, give me your best shot. Am I right, or wrong? Is there a better argument than what I’ve offered?

Works Cited

Beckley, B. D., Callahan, P. S., Hancock, D. W., Mitchum, G. T., & Ray, R. D. (2017). On the “cal-mode” correction to TOPEX satellite altimetry and its effect on the global mean sea level time series. Journal of Geophysical Research: Oceans, 122, 8371–8384. doi:10.1002/2017JC013090

Church, J. A., & White, N. J. (2006). A 20th century acceleration in global sea-level rise. Geophys. Res. Lett., 33. doi:10.1029/2005GL024826

Crok, M., & May, A. (2023). The Frozen Climate Views of the IPCC, An Analysis of AR6. Andy May Petrophysicist LLC.

Jevrejeva, Moore, J., Grinsted, A., Matthews, A., & Spada, G. (2014). Trends and acceleration in global and regional sea levels since 1807. Global and Planetary Change, 113, 11-22. doi:10.1016/j.gloplacha.2013.12.004