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
Thank you for your explanation. A year or two ago I posted the Jevrejeva et al work and noted some of the same items you have noted but not as complete as your explanation. One point of contention that arose was associated with onshore reservoirs removing water that would otherwise drain into the oceans and increase sea level. There are papers on this and I probably have some saved but I can’t recall those references just now. I got in to a rather viscus exchange with another scientist on this topic which I regret. Another person took exception with me for downloading the Jevrejeva data and using it to draw my own conclusions – said the data was not suppose to be used that way.
I appreciate your comparisons with tidal variations and the difference between the Atlantic and Pacific levels for Panama.
Regards, J. Higginbotham
Only one comment is posted. Where are the other two?
Hi Denis,
I don’t know, I have no pending comments, all are approved. I only see one comment from you and it was posted 13 days ago. It was about thorium reactors. I already applied. If it isn’t too much trouble, can repost the other two?
Andy, my non-posted comment concerned a paper by USGS geologists about paleo sea levels covering the past 6,000 years. The paper concluded that sea levels have been rising over this period at a rate of 1-2 mm/yr with lots of ups and downs. Perhaps it made it to the Russian embassy but not you.
I guess, sorry it didn’t make it through. But the 1-2 mm/yr number is the best rate we have right now. It has been higher since the 1990s, but the AMO is on an upswing and I don’t trust a rate based on less than 70-90 years anyway.
Andy,
Thank you for your work and excellent posts. The obvious ping one might expect is from folks who say, “But wait, you’re not showing the most recent data… What about the last 15 years not shown in the plots… perhaps tide gauges up through this year would help?” I get these types of questions in presentations I make and while the updated data do not change the story, this pesky question is set aside.
Thanks again for your work!
I don’t know of any published analysis of tide gauge data past what I show in this post. As you can imagine these reconstructions from raw tide gauge data are a lot of work, and I guess now that satellite data is available no one thinks it is worth the trouble. That means we will have to wait until we have 70-90 years of satellite data. I certainly do not want to mix the two measures at this point in time.
Anyway, we are at the top of the AMO cycle, once it starts to decline all measures of sea level will probably slow or go negative.