Guest essay by Albert Parker
We may consider all the tide gauges in the latest PSMSL survey of relative mean sea level secular trends (http://www.psmsl.org/products/trends/trends.txt ). The population changes year after year, and since 2015, also the method to compute the rates of rise has changed. As PSMSL says “Please note that we changed the method of calculating relative sea level trends in 2015. The trends displayed here are not directly comparable with any calculated before that date.” So, we will focus only on this survey.
The survey includes 722 tide gauges, some of them having not enough data to infer any reliable trend. The global data set has a naïve average rate of rise of 1.39 mm/year, maximum value of +10.25 mm/year and minimum value of -17.63 mm/year.
As we know the short and incomplete records overrate the relative rate of rise of sea levels, we may then consider subsets.
- If we consider all the tide gauges that started recording before 1934 (S1) this subset of 158 tide gauges has a naïve average relative rate of rise of +0.03 mm/year, maximum +6.75 mm/year, minimum -8.09 mm/year.
- If we consider all the tide gauges with at least 70 years of recorded data in 2014 (S2) this subset of 157 tide gauges has a naïve average relative rate of rise of +0.08 mm/year, maximum +6.75 mm/year, minimum -13.22 mm/year.
- If we finally consider all the tide gauges with at least 60 years of recorded data in 2014 (S3), this subset of 212 tide gauges has a naïve average relative rate of rise of +0.41 mm/year, maximum +9.41 mm/year, minimum -13.22 mm/year.
The longer subsets may serve to assess the presence (or absence) of an acceleration, as the relative sea level rates of rise become significant only after the minimum 60 years of data are recorded. The different values only reflect the different populations, with more tide gauges recently being established in areas subject to subsidence rather than uplift. The subsidence of the instrument is still the most relevant component to sea level rise.
What we learn from this survey? The sea levels are not rising, but rising and falling. And in the best “spots” along the world coastlines where the sea level rises are measured and not computed, the naïve average rate of rise is a pretty constant value and a quite small value.
These naïve average relative rate of rise translate in a naïve average sea level rise over the first 15 years of this century no matter the anthropogenic carbon dixoide emission of a little bit less than half a millimetrie to little bit more than one millimetre in the 158 or the 157 long term tide gauges S1 and S2, or at the most in 6 millimetrs in the 212 tide gauges S3 satisfying the minimum requirement of 60 years to infer a reliable trend.
Figure 1 below is the histogram of the S2 data set (tide gauges with more than 70 years of recorded data), image from the Wessa online facility.
The naïve average is practically zero, somewhere the sea level rise, somewhere else the sea level falls. We do not need more and more layers of burocrats and more and more taxes with the excuse to save the world from the rising seas because we burn carbon and hydrocarbon fuels.
Wessa P., (2015), Histogram (v1.0.15) in Free Statistics Software (v1.1.23-r7), Office for Research Development and Education, URL http://www.wessa.net/rwasp_histogram.wasp/