English: This figure shows the change in annually averaged sea level at 23 geologically stable tide gauge sites with long-term records as selected by Douglas (1997). The thick dark line is a three-year moving average of the instrumental records. This data indicates a sea level rise of ~18.5 cm from 1900-2000. Because of the limited geographic coverage of these records, it is not obvious whether the apparent decadal fluctuations represent true variations in global sea level or merely variations across regions that are not resolved.

For comparison, the recent annually averaged satellite altimetry data [1] from TOPEX/Poseidon are shown in red. These data indicate a somewhat higher rate of increase than tide gauge data, however the source of this discrepancy is not obvious. It may represent systematic error in the satellite record and/or incomplete geographic sampling in the tide gauge record. The month to month scatter on the satellite measurements is roughly the thickness of the plotted red curve.

Data: Original data for this figure is from the Permanent Service for Mean Sea Level [2] (PSMSL). Douglas (1997), defined the following criteria for selecting records from the PSMSL which were long, reliable, and avoided large vertical geologic changes:

1. Each record should be at least 60 years in length
2. Not be located at collisional plate boundaries
3. At least 80% complete
4. Show reasonable agreement at low frequencies with nearby gauges sampling the same water mass
5. Not be located in regions subject to large post-glacial rebound

He subsequently identified 24 PSMSL records meeting all five of these criteria:

1. Auckland, 1903-2000
2. Balboa, 1908-1996
3. Brest, 1807-2000
4. Buenos Aires, Argentina, 1905-1987
5. Cascais, 1882-1993
6. Cristobal, 1909-1980
7. Dunedin, 1900-1998
8. Fernandina, 1897-2003
9. Genova, 1884-1997
10. Honolulu, 1905-2003
11. Key West, 1913-2003
12. Lagos, 1908-1999
13. La Jolla, 1924-2003
14. Lyttelton, 1924-2000
15. Marseille, 1885-2000
16. Newlyn, Cornwall, 1915-2003
17. Pensacola, 1923-2003
18. Quequen, 1918-1982
19. San Diego, 1906-2003
20. San Francisco, 1854-2003
21. Santa Cruz de Tenerife, 1927-1990
22. Santa Monica, 1933-2003
23. Trieste, 1905-2001
24. Wellington, 1901-1988

After slight corrections following Douglas (1997) for any remaining post-glacial rebound at these sites (typically ~3 cm/century), the tide gauge data from these sites were plotted in no particular order as the thin lines in the above figure. One site, Wellington, was omitted because the author of this figure was unable to locate the corresponding record from the PSMSL.