Sea level rise and the Greenhouse effect

A large proportion of the world’s population lives in coastal areas vulnerable to rising sea levels. Permanent submersion, repeated flooding, faster erosion of cliffs and beaches, increasingly saline estuaries and salt contamination of groundwater are just some of the possible consequences of a rise in sea level in low-lying regions.


Combined map of regional patterns of observed sea level (in mm/year). This map can be obtained using gridded, multi-mission Ssalto/Duacs data since 1993, which enable the local slopes to be estimated with a very high resolution (1/4 of a degree on a Cartesian projection). Isolated variations in MSL are thus revealed, mainly in the major ocean currents and ENSO events (Credits EU Copernicus Marine Service, CLS, Cnes, Legos)

As global temperatures rise, mean sea level is rising with them: all the indicators point to an increase in the mean level of the world’s oceans. As far as we can tell from a few isolated measurements taken around 1900, this rise has been continuing for at least a century. Today, thanks to the global coverage of altimetry satellites, estimates of the rise in sea level have improved in accuracy. With time series containing fifteen years of data, we can begin to observe trends and attempt to mitigate their effects.


Mean Sea Level variation computed from altimetry 1993-2017 (Credits CLS/Cnes/Legos)

Altimetry provides a powerful tool for determining the extent and causes of sea level change. Since early 1993, Topex/Poseidon has been measuring global sea level variations with great accuracy, complemented and followed by Envisat and Jason-1. This long dataset indicates that, in terms of the global mean, sea level is presently rising at a significantly higher rate than the mean rate recorded by tide gauges for the past five or more decades (of the order of 1.8 +/- 0.3 mm/yr). The higher rate observed during the 1990s may indicate that sea level rise is accelerating due to greater land ice melting and/or increased ocean warming. Moreover, we cannot exclude the possibility that it at least partly reflects the decadal variability of the combined change in thermal and ocean mass. Longer datasets are needed to discriminate between the different hypotheses and to study this question further.
Estimating mean sea level change and its sources is currently a very active research topic. Many teams are participating in fine-tuning the computations and studying the causes.

 

Further information:

Nerem, R.S. and G.T. Mitchum, Sea level change, Satellite altimetry and Earth sciences, L.L. Fu and A. Cazenave Ed., Academic Press, 2001
Nerem R.S., E; Leuliette and Cazenave A., Present-day sea level change, C.R. Geosciences, in press, 2006.
A. Cazenave, A. Lombard, R.S. Nerem, and K. DoMinh, Present-day sea level rise: do we understand what we measure?, 15 years of progress in radar altimetry Symposium, Venice, Italy, 2006
Church, J.A., N.J. White, R. Coleman, K. Lambeck and J.X. Mitrovica, Global and regional sea-level rise, Papers of Note. Bulletin of the American Meteorological Society, 85 (7): 950-952, 2004.
http://www.aviso.altimetry.fr/msl/ (Aviso/Altimetry, Mean Sea Level in cooperation between LEGOS, CLS and CNES)
http://sealevel.colorado.edu/ (University of Colorado at Boulder, USA)
http://copes.ipsl.jussieu.fr/Workshops/SeaLevel/ (Understanding Sea-level Rise and Variability Workshop, June 2006)