This interesting discussion from the Coastal Engineering Manual, which pre-dates the blow-up over “Climategate,” “Glaciergate,” and all of the other “gates” that the science has experienced lately:
Before engineering and management can be considered, a fundamental question must be asked: Is sea level still rising? During the last decade, the media has “discovered” global warming, and many politicians and members of the public are convinced that greenhouse gases are responsible for rising sea level and the increased frequency of flooding that occurs along the coast during storms. Most scientists accept the findings that the concentrations of greenhouse gasses in the atmosphere have increased greatly in the last century, largely due to industrial and automobile emissions. However, the link between increased gas in the atmosphere and changing sea level is much more difficult to model and verify. Wunsch (1996) has pointed out how difficult it is to separate myth from fact in the politically and emotionally charged issues of climate change and the oceans. The Environmental Protection Agency created a sensation in 1983 when it published a report linking atmospheric carbon dioxide to a predicted sea level rise of between 0.6 and 3.5 m (Hoffman, Keyes, and Titus 1983). Since then, predictions of the eustatic rise have been falling, and some recent evidence suggests that the rate may slow or even that eustatic sea level may drop in the future (Houston 1993).
(b) Possibly more reliable information on Holocene sea level changes can be derived from archaeological sites, wave-cut terraces, or organic material. For example, Stone and Morgan (1993) calculated an average rise of 2.4 mm/year from radiocarbon-dated peat samples from Santa Rosa Island, on the tectonically stable Florida Gulf coast. However, Tanner (1989) states that difficulties arise using all of these methods, and that calculated dates and rates may not be directly comparable.
(c) Based on an exhaustive study of tide records from around the world, Emery and Aubrey (1991) have concluded that it is not possible to assess if a eustatic rise is continuing because, while many gauges do record a recent rise in relative sea level, an equal number record a fall. Emery and Aubrey state (p. ix):
In essence, we have concluded that ‘noise’ in the records produced by tectonic movements and both meteorological and oceanographic factors so obscures any signal of eustatic rise of sea level that the tide gauge records are more useful for learning about plate tectonics than about effects of the greenhouse heating of the atmosphere, glaciers, and ocean water.
They also state (p. 176):
This conclusion should be no surprise to geologists, but it may be unexpected by those climatologists and laymen who have been biased too strongly by the public’s perception of the greenhouse effect on the environment….Most coastal instability can be attributed to tectonism and documented human activities without invoking the spectre of greenhouse-warming climate or collapse of continental ice sheets.
(d) In summary, despite the research and attention devoted to the topic, the evidence about worldwide, eustatic sea level rise is inconclusive. Estimates of the rate of rise range from 0 to 3 mm/year, but some researchers maintain that it is not possible to discover a statistically reliable rate using tide gauge records. In late Holocene time, sea level history was much more complicated than has generally been supposed (Tanner 1989), suggesting that there are many perturbations superimposed on “average” sea level curves. Regardless, the topic is sure to remain highly controversial.
The papers cited here are as follows:
- Wunsch, C. 1996. Doherty Lecture: “The Ocean and Climate – Separating Myth from Fact,” Marine Technical Society Journal, Vol 30, No. 2, pp 65-68.
- Hoffman, J. S., Keyes, D., and Titus, J. G. 1983. “Projecting Future Sea Level Rise; Methodology, Estimates to the Year 2100, and Research Needs,” Report 230-09-007, U.S. Environmental Protection Agency, Washington, DC.
- Houston, J. R. 1993. “Responding to Uncertainties in Sea Level Rise,” The State of Art of Beach Nourishment, Proceedings of the 1993 National Conference on Beach Preservation Technology, The Florida Shore & Beach Preservation Association, Tallahassee, FL, pp 358-372.
- Stone, G. W., and Morgan, J. P. 1993. “Implications for a Constant Rate of Relative Sea-Level Rise During the Last Millennium Along the Northern Gulf of Mexico: Santa Rosa Island, Florida,” Shore and Beach, Vol 61, No. 4, pp 24-27.
- Tanner, W. F. 1989. “New Light on Mean Sea Level Change,” Coastal Research, Vol 8, No. 4, pp 12-16.
- Emery, K. O., and Aubrey, D. G. 1991. Sea Levels, Land Levels, and Tide Gauges, Springer-Verlag, New York, NY.
Evidently Al Gore didn’t make the Coastal Engineering Manual bedtime (or pot) reading.