By Andy May
We’ve all heard the question. We show that there is no evidence that current climate changes, whether human-caused or natural, are dangerous or unusual. We were then asked “What about sea level rise? Isn’t that dangerous? There are many very convincing technical arguments why the current rate of sea level rise will not threaten people, New York City, Miami or Tuvalu. These are urban legends stemming from silly IPCC models as explained by Ole Humlum in Chapter 10 of our latest book (Crok & May, 2023). How are these myths quickly refuted in clear language? Here’s my best effort in ~600 words. Let me know how I did.
The current rate of global sea level rise is below the precision of our current ability to measure it as discussed in Chapter 5 by Kip Hansen in Crok & May. Figure 1 shows three respected estimated rates. Sea levels are displayed as reported and they have different zero points. Jevrejeva et al. The blue estimate is 2 mm/year (± ~ 0.3), the estimate below is the Cathedral and White estimate of 1.7 (± ~ 0.3) mm/year. Both of these estimates come from tide gauges, although Jevrejeva’s estimate does try and include satellite data from 1993 to 2009. Due to the overlap in the authors’ estimates of uncertainty , these two estimates are statistically equivalent.
The lower estimate, shown in gray, uses all NASA satellite data since 1993. It suggests 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 another 60 years of data before we can derive meaningful rates from the satellite. Satellite data only cover the ascending portion of the ~60-year cycle or oscillation that began in 1991.
Global average sea levels have been rising over the past 170 years, but the rate is cyclical. This cycle appears prominently in Figure 1 from about 1930 to 1991 in Jevrejeva et al. reconstruction. It is also seen, although in a lighter way, in the reconstruction of the Church and the White People. Therefore, any estimate of the rate of rise based on reconstructions (satellite, tide gauge or combined) shorter than 90-120 years is erroneous. Sea level fell during the Little Ice Age until around 1861 when it began to rise.
All rates (from 1900) are projected to 2100 in the top left box and show a sea level rise of 5 to 10 inches by 2100. These increases are much less than the sea level range. The average daily tide is more than one meter. Such a small increase in 76 years can hardly be noticed. It should be noted here that sea levels are not the same in all oceans as one would expect. In Panama, sea levels on the Pacific side of the country are 20 cm (~8 inches) higher than on the Atlantic/Caribbean side, which speaks to the expected global sea level rise between now and 2019. 2100. Even more important is that the tidal range on the Pacific side is much greater than on the Caribbean side.
Measuring global mean sea level becomes extremely difficult due to variations in mean sea level from ocean to ocean and associated changes in the daily tidal range. Jevrejeva points out that tide gauges are limited to continental and island margins and that most of them are in the Northern Hemisphere, that tide gauge records do not cover the same time period and that they are tied to the region. The land sometimes rises and falls on its own. Jevrejeva points out that it is not easy to combine different metrics into a single global sea level curve.
In the same way, any estimate of the rate of acceleration with any of these data or any combination thereof is a guess. Polynomial fits to all of these series may show some acceleration, but fits to polynomials are not statistically different from linear fits to the same data.
As many of my regular readers know, I often submit ideas for comment. I want to know what the best arguments are against my idea. Or have I missed a better argument? So, positive or negative, give me your best photo. Am I right or wrong? Is there a better argument than what I’ve given?
Beckley, BD, Callahan, PS, Hancock, DW, Mitchum, GT, & Ray, RD (2017). On the “cal mode” correction to the altitude of the TOPEX satellite and its influence on 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). Global sea level rise in the 20th century. Geophysics. Res. Lett., 33. doi:10.1029/2005GL024826
Crok, M., & May, A. (2023). IPCC Glacial Climate Perspective, AR6 Analysis. Physicist Andy May LLC.
Jevrejeva, Moore, J., Grinsted, A., Matthews, A., & Spada, G. (2014). Global and regional sea level rise and trends since 1807. Global and planetary change, 113, November 22. doi:10.1016/j.gloplcha.2013.12.004
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