Satellite Observations of Sea Level Change: What have we learned?
Nerem, R. Steven
University of Colorado, UNITED STATES
With the launch of TOPEX/Poseidon (T/P) in 1992 and the subsequent launch of Jason-1 (2001) and Jason-2 (2008), we now have a precise 20-year continuous record of sea level change. Two more developments fundamentally improved our capability to study the causes of sea level change: the launch of the GRACE satellite gravity mission in 2002 and the establishment of the Argo network of profiling floats shortly thereafter. Together, satellite altimetry, satellite gravity, and in situ measurements have provided unprecedented insight into the magnitude, spatial variability, and causes of present-day sea level change. When compared to the historical record of sea level change from the tide gauge network, the satellite record can be placed in context. The rate of sea level change observed during the altimeter era is roughly double the long-term rate observed by the tide gauges, but the causes of this are still being investigated. The satellite measurements also give a perspective on the spatial variability of sea level change not possible with only tide gauge measurements, and this has led to increased understanding of the spatial variability of sea level change and how it evolves over time. The three measurement systems close the sea level budget within their error bars, i.e., total sea level measured by satellite altimetry equals the ocean mass change measured by GRACE plus the thermosteric sea level change measured by the Argo network. The recent advances in our understanding of sea level change due to the satellite measurements will be reviewed and future research will be discussed. These are powerful tools for understanding sea level change and it is imperative that they be continued.