PRESENT-DAY SEA LEVEL CHANGE:
OBSERVATIONS AND CAUSES
Anny Cazenave
LEGOS-GRGS/CNES, Toulouse, France
Abstract:
In this presentation, we fist discuss observations of global mean sea level variations based on
satellite altimetry and in situ tide gauges, at interannual to decadal time scales. Then we
investigate climate-related processes potentially responsible for the observed variations of the
global mean sea level. We focus on thermal expansion of the oceans and continental water mass
balance. We show that during the 1990s where global mean sea level change has been measured
by Topex/Poseidon satellite altimetry, thermal expansion is the dominant contribution to the
observed 2.5 mm/yr global mean sea level rise. During the 1900s and past few decades, exchange
of water between continental reservoirs and oceans had a small, but not totally negligible
contribution (about 0.2 mm/yr mean sea level rise). For the last four decades, thermal
contribution is estimated to about 0.5 mm/yr, with a possible accelerated rate of thermosteric rise
during the 1990s. We discuss possible causes of the discrepancy between tide gauge-derived
mean sea level rise for the 20th century and climate-related processes. Finally we present the new
perspectives expected from the recently launched JASON and GRACE missions for precisely
measuring global sea level change (with JASON), and determining land water mass contribution
(with GRACE) and thermal expansion (by combining JASON and GRACE data).