1903-1959. Subject to considerable assumption, the rate of RSL increase 

 associated with this pattern was 15 cm/century. A similar analysis of the 

 period 1930-1975 again showed RSL increasing on average everywhere but in the 

 western half of the North Pacific Ocean. Decrease of RSL in this areas was 

 substantiated by hydrographic data. Thus, in recent years the concept of a 

 "global" sea-level rise is not supported. The temporal behavior of the near 

 global signals from both time periods was well approximated by a simple linear 

 trend. There was no evidence of a more rapid rise in RSL in recent years. 



Potential causes of the above RSL change were investigated. Changes in 

 the position of the earth's axis of rotation support the idea that the RSL 

 change was due to approximately equal melting of Greenland/ Antarctica. 

 Changes in the length of day only marginally support this idea. However, 

 other attractive geophysical explanations for variations in both these 

 astronomical parameters exist. Observed change in sea surface temperature 

 (SST) , if representative of reasonable changes in vertical thermal structure, 

 could give the observed RSL change. However, thermal expansion of the oceans 

 would not significantly affect the rotational parameters although changes in 

 these parameters could be due to non-RSL related processes. Changes in ocean 

 circulation and/or subsidence along all the coastal margins simultaneously 

 seem unlikely causes of the observed change in RSL. In the study findings, it 

 is not concluded possible at this time to explain reliably the apparent 

 increase in RSL. (Modified Abstract) . 



008 BARNETT, T. P. 1984. "The Estimation of "Global' Sea-Level Change: A 

 Problem of Uniqueness," Journal of Geophysical Research . Vol 89, No . C5 , 

 pp 7980-7988. 



An objective method of estimating regional averages of coherent sea- 

 level (SL) change is developed. The technique is applied to a large set of SL 

 data representative of most of the world's continental margins. The results 

 show highly coherent SL changes over many of the regions studied. The method 

 is then applied to the regional averages themselves to develop an overall 

 estimate of the coherent pattern of SL variations existing in the historical 

 SL data set. The pattern is characterized by a coherent rise of SL in all 

 regions except Alaska, Scandinavia (both areas of notorious crustal uplift) , 

 and Southeast Asia. The period since that time has seen an increase in SL 

 that is optimally fit by linear trend of 23 cm/century. The study results 

 suggest that it is not possible to uniquely determine either a global rate of 

 change of SL or even the average rate of change associated with the existing 

 (inadequate) data set. Indeed, different analysis methods, by themselves, can 

 cause 50 percent variations in the estimates of SL trend in the existing data 

 set. A signal/noise analysis suggests it should be easy to detect small, 

 future changes in the SL trends estimated for the period 1930-1980. However, 

 detection of theoretically predicted low- frequency signals (e.g. caused by CO2 

 warming) will be difficult in view of the huge, low- frequency , natural vari- 

 ability associated with glacial/tectonic processes. (Author). 



