221 



Vivien M. Gornitz 



Columbia University 



Goddard Institute for Space Studies 



New York, NY 10025 



SECT. 2. ESTIMATES OF EUSTATIC SEA LEVEL RISE 



Previous estimates of the global eustatic sea level change from tide- 

 gage records over the last 100 years cluster between 1.0 and 1.5 mm/yr 

 (Table A. 3). Some studies used single, widely-spaced, representative 

 stations (e.g., Fairbridge and Krebs , 1962; Barnett, 1983), while others 

 grouped many stations into a limited number of geographic regions. Global 

 trends were obtained by averaging of regional averages (Gornitz et al . , 

 1982) or by eigenanalysis (Barnett, 1984; Aubrey and Emery, 1983). 

 However, the latter technique applied to sea level data may have some 

 drawbacks (Solow, 1987). 



More recently, Gornitz and Lebedeff (1987) derived a global sea level 

 trend using a similar averaging approach, outlined in Sect. 2.3 of the 

 Mehta et al. (1987) report discussed herein. Vertical movements determined 

 from ■'-'^C-dated Holocene sea level indicators (Pardi and Newman, 1987) were 

 removed (see below). The global mean corrected sea level change is 1.0 ± 

 0.1 mm/yr (95% confidence interval). The arithmetic mean of corrected 

 least- squares slopes on individual stations is 1.2 ± 0.3 mm/yr (Gornitz and 

 Lebedeff, 1987). Sea level is rising in all but three regions that are 

 characterized by small station populations or sparse long-range data 

 (Fig. A.l). Nevertheless, large regional variations in sea level remain, 

 even after subtraction of long-term trends. Some of the sources of noise 

 in mareograph data (Table A. 4) and means of removing them are briefly 

 discussed below. 



Data Quality and Distribution 



Tide -gage records often are too short, are variable in length, contain 

 data gaps, and are geographically biased. Only around 300 tide stations 

 from the Permanent Service for Mean Sea Level (PSMSL) have usable records 

 of 20 years or longer. Although nearly 90% of the stations lie north of 

 23°N, this represents over 70% of the world's total coast length. 



