Recent changes in sea level and their possible causes |
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Authors: | T P Barnett |
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Institution: | (1) Climate Research Group, Scripps Institution of Oceanography, University of California, 92093 San Diego, La Jolla, California, USA |
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Abstract: | A new analysis of ‘global’ sea level has been made that largely avoids space/time bias of previous works. A coherent pattern
of increasing relative sea level (RSL) was found to exist on average at all stations analyzed between 1903–1969. 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 area was substantiated by hydrographic data. Thus in recent years the concept of a ‘global’ sea level rise
is not supported. The temporal behavior of thenear 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, the SST data are likely biased instrumentally toward increasing trend.
Also, 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 summary, it is not possible at this time to explain reliably the apparent
increase in RSL. |
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