Claims that sea level rise is 3.3 mm/year are looking increasingly like a grand hoax. David A. Burton runs the sea level rise resource site sealevel.info posts an analysis showing sea level rise is only half of what it is claimed to be.
Sea Level Rise Only Matters At The Coasts
By David A. Burton
Many may not be aware of this, but satellite altimeters are incapable of measuring sea-level at the coasts, among other significant problems.
Coastal tide gauges, on the other hand, measure sea-level at this important location – which is where it really matters. Tide gauge measurements of sea-level are far more reliable than satellite altimetry, and of much longer duration. The longest tide-gauge records of sea-level measurements are nearly ten times as long as the combined satellite measurement record, and twenty times as long as any single satellite measurement record.
No sign of any acceleration
NOAA has done linear regression analysis on sea-level measurements (relative sea-level) from 225 long term tide gauges around the world, which have data spanning at least 50 years. (Note: the literature indicates that at least 50-60 years of data are required to determine a robust long term sea-level trend from a tide gauge record.) There’s no sign of any acceleration (increase in rate) in most of those tide-gauge records.
More than 85% of stations show less rise than 3.3 mm/year
The rate of measured sea-level rise (SLR) varies from , to . 197 of 225 stations (87.6%) have recorded less than 3.3 mm/yr sea-level rise. At 47 of 225 stations (20.9%) sea level is falling, rather than rising. Just 28 of 225 stations (12.4%) have recorded more than 3.3 mm/yr sea-level rise.
The average SLR at those 225 gauges is +0.90 mm/yr. The median is +1.41 mm/yr.
That appears to be slightly less than the true global average, because a disproportionate number of those 225 stations are northern hemisphere stations affected by post glacial rebound (i.e., the land is rising faster). On the other hand quite a few long-term tide gauges which are substantially affected by subsidence (i.e., the land is sinking), often due to extraction of water, oil, or natural gas, or due to the location having been elevated with fill dirt which is compacting (Ex.: ).
I downloaded the two sea-level measurement spreadsheet files (U.S. and global) from , and combined them into a single Excel spreadsheet. For ease of sorting I changed the U.S. station ID numbers by adding an “A-” prefix. I also added “average” and “median” lines at the end of the spreadsheet.
The average of all 375 NOAA-analyzed stations is 1.28 mm/yr, and the median is 1.71 mm/yr:
NOAA says that the average is 1.7-1.8 mm/yr. Some of the difference between the calculated average and NOAA’s figure for rise may be due to the addition of model-derived adjustments to the measured rates when calculating the average to account for post glacial rebound (). My guess is that they’re using . Unfortunately, those figures are only very loosely correlated with what is actually happening at the tide-gauge locations.
Prof. Peltier also estimates that melt-water load from the melting of the great ice sheets (~10k years ago) is causing the ocean floors to sink by enough to cause a fall in sea-level, absent other factors. That number (0.3 mm/yr) is usually added to calculated “global average” sea-level rise rates, inflating the reported average, even though the resulting sum is not truly sea-level, and is not useful for projecting sea-level for coastal planning. It’s an attempt to calculate what the rate of sea-level rise would be were it not for the hypothesized sinking of the ocean floor.
50-60 years of data needed to establish trend
Unfortunately, many of the tide station records in NOAA’s expanded list of 375 are too short to be appropriate for measuring sea-level trends. The literature indicates that to establish a robust sea-level trend from a tide station record. But the shortest record in NOAA’s list is Apra Harbor, Guam, with just 21 years of data. The text at the top of NOAA’s page says, “Trends with the widest confidence intervals are based on only 30-40 years of data.” But that is incorrect. I suspect they wrote it before they added the gauges with very short records.
So I also made a version of this spreadsheet in which stations with records shorter than 50 years are omitted.
Considering only tide stations with records of at least 50 years, the average and median rates of MSL rise (of the 225 remaining stations) are 0.90 mm/yr and 1.41 mm/yr, respectively:
I also tried limiting it to stations with records of at least 60 years, with very similar results: average 0.77 mm/yr, and median 1.37 mm/yr.
The average (0.90 mm/yr) is probably unrealistically low, due to the disproportionate number of stations in northern Europe which see low or negative rates of measured sea-level rise due to post glacial rebound. The fact that the average is less than the median also suggests that there are a disproportionate number of low-end outliers.
I also tried another approach, in which I excluded the most extreme latitudes. I started with just the “50+ year” stations, and included only stations within a latitude range of 45 (i.e., I excluded stations above 45 north or below 45 south). The resulting average and median for 137 stations were 2.22 mm/y and 2.02 mm/yr, respectively:
That approach largely solves the problem of low-side bias introduced by stations which are affected by PGR (which lowers the calculated average), but it doesn’t solve the problem of high-side bias introduced by stations affected by subsidence (which raises the calculated average). So the average (2.22 mm/yr) is probably unrealistically high. The fact that the average is greater than the median also suggests that there are a disproportionate number of high-end outliers.
So I tried another approach, this time explicitly eliminating “outliers.” I started with just the “50+ year” stations, but excluded the 40 stations with the lowest rate of sea-level rise (including most of those experiencing falling sea-level), and the 30 stations with the highest rate of sea-level rise (including most of those experiencing severe land subsidence, like Galveston, which is built on sinking fill dirt).
The resulting average and median rates of sea-level rise (calculated from 155 stations) are both 1.48 mm/yr:
That figure, 1.48 mm/yr, is the current best estimate of globally averaged coastal sea-level rise. At first glance excluding more low outliers than high outliers might seem to bias the result to the high end. But I think it is justifiable because of the disproportionate number of northern European and North American stations at locations where the land is rising due to post glacial rebound. The fact that the median and average are equal suggests that there aren’t disproportionate numbers of either high or low outliers.
I also tried excluding the low and high 35 stations, and the result was an average MSL rise of 1.36 mm/yr, and median 1.41 mm/yr, which suggests that it includes more low outliers than high outliers.
Note that 1.48 mm/yr is less than six inches per century. Also if you add Peltier’s +0.3 mm/yr GIA to that calculated 1.48 mm/yr global average rate of MSL rise, the sum is within NOAA’s 1.7-1.8 mm/yr range.
It is not possible to torture the tide-gauge data into yielding a globally averaged rate of relative sea-level rise anywhere near 3.3 mm/yr.”
David A. Burton has a BS in Systems Science from Michigan State University, and an MA in Computer Sciences from the University of Texas at Austin.
He is a Board Member of NC-20, and one of the organization’s Science Advisors. In 2011 he wrote a comprehensive critique of the Coastal Resource Commission’s 2010 North Carolina Sea-Level Rise Assessment Report, identifying numerous serious errors in that document. He was also a member of the NC Sea Level Rise Impact Study Advisory Committee, a member of the NC Portal Project Review Committee, a U.N. IPCC AR5 WG1 Expert Reviewer, and is webmaster of the sealevel.info website.