The measured rate of rise of sea levels is not increasing and climate models should be revised to match the experimental evidence

This is from last year but would seem of interest in the light of the recent Envisat "adjustments" of the sea-level record

Alberto A. Boretti, Research Professor, Missouri University of Science and Technology

The paper by Robert J. Nicholls et al. is pushing upward the already catastrophic predictions of sea level rise (SLR) by 2100 because of the anthropogenic carbon dioxide emissions. The estimation of up to 2 m SLR by 2100 is made assuming the temperatures would increase proportional to the anthropogenic carbon dioxide emissions, and the rate of rise of sea-levels will increase proportionally to the temperatures and therefore proportionally to the anthropogenic carbon dioxide emissions.

The paper omits to consider the experimental evidence made of rates of rise of sea-levels not accelerating at all. Some recent papers [1-3] and data proposed in [4] and [5] provide numbers that contrast the general but wrong perception that the SLR is escalating at present supported by the authors. Analysis of nine long and nearly continuous sea level records over one hundred years (1903-2003) provided a mean value of SLR as 1.74 mm/year with higher values in the earlier part of the 20th century compared to the latter part in [1].

Tide gauge records over a period 1900-2006 provided a mean value of 1.56 mm/year with no statistically significant acceleration in sea level rise [2]. Same paper shows rates immediately before 2007 had been achieved or exceeded over similar time periods at other points during the 20th century with some decades even revealed a fall in global sea level over that period. Analysis of 57 tide gauge records each with a record length of 80 years which include 25 gauges with data from 1930-2010 provided no acceleration in SLR, but instead a small average deceleration of -0.0014 and -0.0123 mm/year2 [3].

The best source of global sea level data is The University of Colorado [4]. Since 1993, measurements from the TOPEX and Jason series of satellite radar altimeters have allowed estimates of global mean sea level (MSL). These measurements are continuously calibrated against a network of tide gauges. When seasonal and other variations are subtracted, they allow estimation of the global mean sea level rate. As new data, models and corrections become available, these estimates are continuously revised (about every two months) to improve their quality.

20 years of MSL data shows increments in SLR much smaller than the 20 mm/year necessary to produce a rise of 200 cm over a century and reducing especially over the last 10 years.

Worth of note is the huge deceleration of SLR considering only the last 10 years of about -0.285 mm/year2 that is clearly the opposite of what is being assumed by the models of SLR sharply accelerating. The average SLR of 2.7 mm/year is only 10% of the SLR needed for the prediction of 2 m rise to be correct.

The average SLR over the last 5 years is also much smaller than the average rate of rise over the last 20 years, and about 1.6 mm/year. The Australian Baseline Sea Level Monitoring Project [5] is designed to monitor sea level around the coast line of Australia. An array of SEAFRAME (SEA-Level Fine Resolution Acoustic Measuring Equipment) stations is used to measure the sea level very accurately and to record meteorological parameters.

These data also support the evidence of SLR absolutely not accelerating.20 years of measurements show increases in the MSL much smaller than the more than 10 mm/year, with all the stations actually having experienced a SLR on average much less than one half of the 10 mm/year. The SLR is also clearly reducing in the last 5 years.

MSL is increasing over the 20 years but without any significant acceleration. SLR is clearly not accelerating or decelerating over the 20 years. The maximum acceleration is 0.5 mm/year2, the minimum acceleration (deceleration) is - 1.2 mm/year2 and the average acceleration (deceleration) is -0.005 mm/year2. Reducing the numbers of years of data to be fitted to 10 and 5 years respectively, the average acceleration decreases (the deceleration increases).

All the data published in [1-3] and the others data proposed in [4] and [5] consistently present rates of rise of sea levels absolutely not accelerating over the last century and this portion of the new century. Therefore, climate models should be revised to match the experimental evidence.


[1] S.J. Holgate. On the decadal rates of sea level change during the twentieth century. Geophysical Research Letters. 2007; 34, L01602.

[2] M. Wenzel and J. Schr?ter. Reconstruction of regional mean sea level anomalies from tide gauges using neural networks. JOURNAL OF GEOPHYSICAL RESEARCH - OCEANS. 2010; 115:C08013.

[3] J.R. Houston and R.G. Dean, Sea-Level Acceleration Based on U.S. Tide Gauges and Extensions of Previous Global-Gauge Analyses. Journal of Coastal Research. 2011; 27:409-417.

[4] [Internet]. [Cited 2011 July 12].

[5]. [Internet]. [Cited 2011 July 12].


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