The notion of sea level rise brings to the popular mind the specter of deep inundation of coastal regions. One pictures skyscrapers emerging from the waters like so many sleeping flamingos standing in the shallows of a lake. Of course if all of the world's ice sheets suddenly melted or collapsed, this vision would apply to New York City and its coastal counterparts. But there is a general consensus that such a calamity is not an immediate threat [ Houghton et al., 1990]. The actual situation for the recent historical past and near future appears to be more benign, but with nonetheless extremely significant, even devastating impacts due to erosion and flooding of coastal areas.
Controversy concerning the significance of the present rate of global sea level rise, and how it may relate to whether the ``greenhouse'' is here or not, is very much in the public sphere (for a few prominent examples see Cory, [1991]; Chui, [1991]). Although the present (meaning the average over the last 100 years or so) rate of rise and its interpretation is subject to a certain amount of disagreement, it is an observed fact that relative sea level is rising in most coastal regions and causing major problems just at the time when rapid coastal development is taking place. If the postulated global warming and associated greatly increased rate of sea level rise occur in the next century, these problems will be exacerbated.
Many important books [ Pugh, 1987; National Research Council (NRC), 1990; Emery and Aubrey, 1991; Woodworth et al., 1992; Warrick et al., 1993; Bird, 1993] and comprehensive reviews [ e.g., Woodworth, 1993; Baker, 1993; Gornitz, 1993, 1994] on the subject of sea level have appeared in recent years. These can be consulted for an exhaustive list of references dealing with sea level rise estimates, and matters involving tidal analyses, measuring sea level, data analysis, and impacts. It is not the purpose of this paper to imitate these reviews, nor the ones cited later concerning such diverse subjects as coastal geomorphology, or how sea level rise is related to climate change. The volumes and papers mentioned above, as well as many of those referenced later, will of necessity find their way into the library of anyone deeply interested in the sea level problem.
Rather, what is intended is (at the request of the editors) to assemble from the many available books, reviews, and papers a view of where the field of sea level research stands today and how further progress can be made. Especially it is desired for this paper to serve as a resource for the non-specialist. This last goal reflects the fact that the study of sea level is interdisciplinary, involving oceanography, geophysics, meteorology, geology, geodesy, coastal geomorphology, and other related and specialized fields.
Recent analyses indicate that global (i.e., eustatic) sea level has risen at something close to 2 mm per year for at least the last century or so [ Peltier and Tushingham, 1989; Trupin and Wahr, 1990; Douglas, 1991], and probably at a much smaller rate for the previous several millennia [ Flemming, 1978; Flemming and Webb, 1986; Kearney and Stevenson, 1991; Shennan and Woodworth, 1992; Varekamp et al., 1992]. In contrast, for the next century various authors plausibly argue that global sea level will rise at a much faster rate than at present because of global warming.
The Intergovernmental Panel on Climate Change (IPCC) report [
Houghton et al., 1990] gives for the ``business-as-usual''
scenario of global warming an additional sea level change of 18 cm
by 2030 and 44 cm by 2070. Church et al. [1991], in an
important and thorough paper, calculate a rise of 35 cm by 2050.
Woodworth [1990] and Douglas [1992] have shown that
such increases require an acceleration of sea level an order of
magnitude greater (about 0.2 mm year
) than the negligible
acceleration observed in the tide gauge record of the last 150
years. Observing and interpreting this small but highly significant
acceleration of global sea level in a timely manner is a critical
aspect of any climate monitoring program.