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Rate of Sea Level Rise: Predictions vs. Measurements

Reference
Boretti, A.A. 2012. Short term comparison of climate model predictions and satellite altimeter measurements of sea levels. Coastal Engineering 60: 319-322.
Boretti (2012) begins his work by noting that in its report of 2007, the IPCC projected that global sea level was likely to rise somewhere between 18 and 59 cm by 2100; but he says that certain "model-based analyses performed recently have predicted much higher sea level rise [SLR] for the twenty-first century," even "exceeding 100 cm if greenhouse gas emissions continue to escalate," citing most pointedly in this regard the studies of Rahmstorf (2007, 2010). However, he notes that studies reaching just the opposite conclusion have also been published, referencing those of Holgate (2007), Wunsch et al. (2007), Wenzel and Schroter (2010) and Houston and Dean (2011).

Working with what he calls "the best source of global sea level data," which he identifies as the TOPEX and Jason series of satellite radar altimeter data, Boretti applies simple statistics to the two decades of information they contain to "better understand if the SLR is accelerating, stable or decelerating." So what did he find?

The Australian scientist reports that the average rate of SLR over the almost 20-year period of satellite radar altimeter observations is 3.1640 mm/year, which if held steady over a century would yield a mean global SLR of 31.64 cm, which is just a little above the low-end projection of the IPCC for the year 2100. However, he also finds that the rate of SLR is reducing over the measurement period at a rate of -0.11637 mm/year2, and that this deceleration is also "reducing" at a rate of -0.078792 mm/year3.


Comparison of MSL predictions from Rahmstorf (2007) with measurements from the TOPEX and Jason series. Adapted from Boretti (2012), who states in the figure caption that "the model predictions [of Rahmstorf (2007)] clearly do not agree with the experimental evidence in the short term."

Commenting on these findings, Boretti writes that the huge deceleration of SLR over the last 10 years "is clearly the opposite of what is being predicted by the models," and that "the SLR's reduction is even more pronounced during the last 5 years." To illustrate the importance of his findings, he notes that "in order for the prediction of a 100-cm increase in sea level by 2100 to be correct, the SLR must be almost 11 mm/year every year for the next 89 years," but he notes that "since the SLR is dropping, the predictions become increasingly unlikely," especially in view of the facts that (1) "not once in the past 20 years has the SLR of 11 mm/year ever been achieved," and that (2) "the average SLR of 3.1640 mm/year is only 20% of the SLR needed for the prediction of a one meter rise to be correct."

Clearly, the more-rabid-than-the-IPCC-crowd has it all wrong when it comes to both sea level and climate, for as Boretti concludes, "the oceans are truly the best indicator of climate," and what they suggest is not compatible with what those alarmed about climate change continually claim.

Additional References
Holgate, S.J. 2007. On the decadal rates of sea level change during the twentieth century. Geophysical Research Letters 34: 10.1029/2006GL028492.

Houston, J.R. and Dean, R.G. 2011. Sea-level acceleration based on U.S. tide gauges and extensions of previous global-gauge analyses. Journal of Coastal Research 27: 409-417.

Rahmstorf, S. 2007. A semi-empirical approach to projecting future sea-level rise. Science 315: 368-370.

Rahmstorf, S. 2010. A new view on sea level rise: has the IPCC underestimated the risk of sea level rise. Nature Reports Climate Change: 10.1038/climate.2010.29.

Wenzel, M. and Schroter, J. 2010. Reconstruction of regional mean sea level anomalies from tide gauges using neural networks. Journal of Geophysical Research 115: 10.1029/2009JC005630.

Wunsch, C., Ponte, R. and heimbach, P. 2007. Decadal trends in sea level patterns: 1993-2004. Journal of Climate 20: 5889-5911.

Archived 8 August 2012