final_program_abstracts[1]

11 IMSC Session Program
Reconstruction of global sea levels over the 20th century
Monday - Parallel Session 4
R. D. Ray 1 and B. C. Douglas 2
1 NASA Goddard Space Flight Center, Greenbelt, USA
2 Florida International University, Miami, USA
Global sea level rise over the past century has usually been determined by analyzing
long time series of measurements from a small number of coastal tide gauges. That
task is considerably complicated by large interannual and decadal variability in the
records, which is unrelated to global sea-level rise. Large variability at isolated
stations also frustrates accurate determination of the much smaller decadal variability
in global mean sea level; the existence of the latter is now well established by two
decades of precise satellite altimetry. One approach to overcome these issues is to
form a time series of near-global sea-level maps, whose individual global means are
less sensitive to the isolated variability at single stations. This can be done by
combining—hopefully in some optimal sense—the spatial structure of sea level, as
determined by satellite altimetry, with the temporal structure from tide gauges.
Kaplan and colleagues have used this approach to reconstruct global sea-surface
temperatures and pressures since 1850, and Church and colleagues have adopted the
method for historical sea levels. We here reexamine several aspects of the sea level
reconstruction. Of primary concern is that the reconstruction methods assume the
spatial structures and correlations recently observed by altimetry remain stationary
throughout the whole reconstruction period. We have strong doubts that this can be
the case. The altimeter time series is now long enough that the this can be partially
explored by realistic modifications of the spatial interpolation functions. We also
explore the sensitivity to the number and distribution of tide gauges. The tide-gauge
sea level trends are potentially biased by vertical land motion, which is induced by
both glacial rebound and by tectonic processes near the sites. We explore the
sensitivity of the sea-level reconstruction to realistic errors in the landmotion
corrections.
Abstracts 62