The complete meltdown of the Greenland and Antarctic ice sheets would raise the sea level 65 meters, whereas a partial meltdown only a few tens of meters. Eustatic sea level rates of changes in Greenland since 2003 show a net ice mass reduction of 96 gigatons per year; with this, geologists are called upon to add a historical perspective upon these changes.
Pre-Neogene continental rearrangements occurred at numerous episodes, masking the net effects of eustatic level fluctuations. Glacial advance is prominent during late Precambrian, late Carboniferous and Pleistocene. Greenhouse events and temperature increases are evident during the Devonian and Cretaceous. Paleo-continental landmass positions reveal a direct relationship to icehouse and greenhouse events. The restriction of global oceanic circulation at the equator brings about icehouse events. Absolute rates of change for comparison purposes to the present are currently impossible due to the multivariate effects (1) tectonic plate motion world wide; (2) variations in sedimentary processes; (3) diagenetic change in sedimentary rock; (4) subsidence, on the resultant stratigraphic record.
Since carbonate reefs reach the top of the subsea or photic zone, carbonate reef growth is an ideal indicator of sea level change. Carbonate deposits at the Caribbean — South America plate boundary are a prime example that plate motion can greatly supersede sea level fluctuations. The best areas to use carbonate reef data is along the Florida-Bahamas-Caribbean passive margins of the Atlantic basin, where Neogene tectonics and carbonate deposition were stable. The carbon dioxide levels were much greater above the K/T boundary, creating an environment devoid of significant carbonate buildups. The earliest significant quantitative sea-level rate of change data is derived from wells drilled into stable carbonate platforms of the late Neogene 2–7 Ma, when carbon dioxide levels decreased in the atmosphere. Cores show rates of paleo sea level rise averaging 10 to 20 cm/100yr versus currently between 17–32cm/100yr. The rate increase has nearly doubled within the past 14 years. This increased rate of change in sea-level has been recently highlighted at the 2007 Intergovernmental Panel on Climate Change in Paris, France.
In the past, rapid warming caused extreme increase in eustatic sea level rates of change reflected in geochemical data from carbonate Holocene reef cores from the west side of Barbados Island, drowned reefs off the, Florida coast, and from Bermuda. The measuring sea level changes of 1–2m/100yr are evident from 13,000–17,000 years ago. The warming is attributed to solar irradiance at glacial maximum during the Wisconsinan 14,000–20,000 years before present when sea level was as much as −175 meters lower than today. This lowered sea level evidence is derived from Holocene reefs south of the Great Barrier Reef in Australia. Bluemle (2001) characterizes the Holocene as a sequence of ten or more global scale “little ice ages” fairly irregularly spaced, each lasting a few centuries and separated by global warming events shown from the ice core data. Friedman (2005) noted an overall cooling trend in ocean waters based on Red Sea beach rock geochemical data from 7,000 to 2,000 years ago. Through all the erratic temperature swings over the past 4,000 years geochemical data from Holocene reef cores from Florida show a sea level rise of 12cm/100yr., typical of stable geological and climatological periods.
The Questions remains: Is the current rate change of sea level significant or, just another unanswered anomaly from the cycle curve?