Estimates of the Current Rate of Sea Level Rise per se

Since the peak of the last ice age the sea level has risen about 360 feet. That is 360 feet in 18,000 years, or about 24 inches per century. There is no reason to believe that that trend has ended. The current rate of rise is however much less than this average. It has not been easy establishing what the current rate of rise is. The big problem is establishing the vertical movement of the land mass where the sea level gauges are located. A team under the leadership of G.B. Wöppelmann made use of Global Positioning System (GPS) networks that gave them 160 stations located within the vicinity of tidal gauges. Using this data the land rise over the period from January 1999 to August of 2005 was established. From this the team established that the rate of rise of the sea level is 1.31 ± 0.30 mm per year. This was substantially less than the estimate of 3.1 mm per year given by the Intergovernmental Panel on Climate Change (IPCC); a reduction of 58 percent. In other words the UN estimate was a 237 percent overestimate. The value of 3.1 mm per year itself is not a large amount; it is 0.31 meters or 12 inches per century. The Wöppelman estimate is about 5 inches per century. The Wöppelman et al study was published in 2007 in the journal Global and Planetary Change under the title "Geocentric Sea-Level Trend Estimates from GPS Analysis at Relevant Tidal Guages Worldwide." (pp. 396-406)

In the very fine book Sea Level Rise: History and Consequences, edited by Bruce C. Douglas, Michael S. Kearney, Stephen P. Leatherman there is cited the case of Sharp's Island, Maryland in the Chesapeake Bay. At the time of the original settlement of Maryland this island was about 700 acres in size. In 1850 it was down to about 600 acres. By 1910 its area was down but still at least 300 acres. By the year 2000 Sharp's Island had disappeared. This was not due to a rise in the sea level alone.

With the rebound of the northern part of the North American tectonic plate the middle and southern part will subside taking with it some low lying islands. The peninsula of Florida could be sinking. This book contains an article by W. Sturges and B.G. Hong entitled "Decadal Variability of Sea Leve" which provides information on the low frequency, long wavelength ocean waves induced by winds, which was mentioned above.

The Volumes of the Earth's Major Reservoirs of Water

The Flows to and from Earth's Major Reservoirs of Water

Note that the flows given are balanced. The flow deficit of the oceans of 37 trillion cubic meters due to the water loss from evaporation exceeding the rainfall is made up by 37 trillion cubic meters of water flowing from the land to the oceans. The flows of water to and from the atmosphere in a year greatly exceed in magnitude the amount of water held in the atmosphere at any one time.

The Little Ice Age was a period of about a half millenium which brought a temporary halt in the retreat of glaciers but after it ended around 1850 there has been a resumption of the glacial retreat.

Conclusions

The best estimate of the current rate of rise in the sea level is 1.3 mm per year. That is 13 cm or 5 inches per century. The upper and lower confidence limits based upon the Wöppelmann measurement are 10 cm (4 in) and 16 cm (6.3 in). The Government of the Maldives Islands should have a hard time justifying reparation payments from the developed nations of the world for that degree of rise.

The Intergovernmental Panel on Climate Change (IPCC) now projects a sea level rise of between 7 inches and 24 inches by the year 2100. This was based upon a projected increase in global temperatures. The range reflects the lack of informed knowledge on the matter or a realization that a range of completely unsupported figures sounds more scientific and objective than a single figure estimate.

(To be continued.)