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How High Will the Sea Level Rise by the End of the 21st Century?
Volume 14, Number 13: 30 March 2011

In the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Bindoff et al. (2007) projected a mean global sea level rise somewhere in the range of 18-59 cm relative to mean global sea level in 1990. Subsequently, however, based on statistical models that employ semi-empirical relationships between past and predicted future increases in global temperature, Vermeer and Rahmsdorf (2009), Jevrejeva et al. (2010) and Grinsted et al. (2010) derived much greater increases on the order of 60 to 190 cm over the same time interval. And now -- based on sea level behavior between 1930 and 2010, as derived from United States tide gauge data, plus extensions of previous global-gauge analyses -- a new empirical study, which does not rely on a relationship between sea level and temperature, casts doubt upon both sets of projections.

Houston and Dean (2011) began their analysis of the subject by noting that global sea level increases of 60-190 cm between 1990 and 2100 would require mean global sea level rate-of-rise accelerations of 0.07-0.28 mm/year/year above the mean global rate-of-rise of the past several decades, which latter rate has typically been calculated to fall somewhere between 1.7 and 1.8 mm/year. Working with the complete monthly-averaged records of 57 U.S. tide gauges archived in the Permanent Service for Mean Sea Level data base that had lengths of 60-156 years (with a mean time span of 82 years), however, they determined that there had not been any acceleration in the rate-of-rise of the sea level along the shorelines of the United States over that period of time, during which interval the world's climate alarmists claim the planet had warmed at a rate and to a level that were unprecedented over the past one to two millennia. Quite to the contrary, in fact, they detected a slight deceleration of -0.0014 mm/year/year. And working with 25 of the tide gauge records that contained data for the period 1930-2010, they calculated an even larger deceleration of -0.0130 mm/year/year.

The two researchers also report that they "obtained similar decelerations using worldwide-gauge records in the original data set of Church and White (2006) and a 2009 revision (for the periods of 1930-2001 and 1930-2007) and by extending Douglas's (1992) analyses of worldwide gauges by 25 years." Consequently, they rhetorically ask why the concomitant worldwide-temperature increase "has not produced acceleration of global sea level over the past 100 years," and, indeed, "why global sea level has possibly decelerated for at least the last 80 years."

Clearly, the reality of the world is vastly different from what is portrayed by the IPCC and the world's climate alarmists, based on simulations produced by state-of-the-art climate models. And the empirical facts of this particular "detective case" suggest something much less ominous than what they are predicting for earth's future with regard to the magnitude of sea level change over the remainder of the 21st century.

Sherwood, Keith and Craig Idso

Bindoff, N.L., Willebrand, J., Artale, V., Cazenave, A., Gregory, J., Gulev, S., Hanawa, K., Le Quere, C., Levitus, S., Noijiri, Y., Shum, C.K., Talley, L.D. and Unnikrishnan, A. 2007. Observations: oceanic climate change and sea level. In: Solomon, S. et al. (Eds.), Climate Change 2007: The Physical Science Basis. Intergovernmental Panel on Climate Change, Cambridge University Press, New York, New York, USA.

Church, J.A. and White, N.J. 2006. 20th century acceleration in global sea-level rise. Geophysical Research Letters 33: 10.1029/2005GL024826.

Douglas, B.C. 1992. Global sea level acceleration. Journal of Geophysical Research 97: 12,699-12,706.

Grinsted, A., Moore, J.C. and Jevrejeva, S. 2010. Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD. Climate Dynamics 34: 461-472.

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.

Jevrejeva, S., Moore, J.C. and Grinsted, A. 2010. How will sea level respond to changes in natural and anthropogenic forcings by 2100? Geophysical Research Letters 37: 10.1029/2010GL042947.

Vermeer, M. and Rahmsdorf, S. 2009. Global sea level linked to global temperature. Proceedings of the National Academy of Sciences USA 106: 21,527-21,532.