Les variations actuelles du niveau de la mer : Observations et causes.

Abstract : Whereas sea level has changed little over the last 2000 years, it has risen at a rate of about 2 mm/year during the 20th century. This unexpected sea level rise has been attributed to the anthropogenic global warming, recorded over several decades. Sea level variations have been measured globally and precisely for about 12 years due to satellite altimeter missions Topex/Poseidon and Jason-1. These observations indicate a global mean sea level rise of about 3 mm/year since 1993, a value significantly larger than observed during previous decades.
Recent observations have allowed us to quantify the various climatic factors contributing to observed sea level change : thermal expansion of sea water due to ocean warming, melting of mountain glaciers and ice sheets, and changes in the land water reservoirs. A water budget based on these new observations allows us to partly explain the observed sea level rise. In particular, we show that the thermal expansion explains only 25% of the secular sea level rise as recorded by tide-gauges over the last 50 years, while it contributes about 50% of sea level rise observed over the last decade. Meanwhile, recent studies show that glacier and ice sheet melting could contribute the equivalent of 1mm/year in sea level rise over the last decade.
In addition, the high regional variability of sea level trends revealed by satellite altimetry is mainly due to thermal expansion. There is also an important decadal spatio-temporal variability in the ocean thermal expansion over the last 50 years, which seems to be controlled by natural climate fluctuations. We question for the first time the link between the decadal fluctuations in the ocean thermal expansion and in the land reservoirs, and indeed their climatic contribution to sea level change. Finally a preliminary analysis of GRACE spatial gravimetric observations over the oceans allows us to estimate the seasonal variations in mean sea level due to ocean water mass balance variations.
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Submitted on : Wednesday, June 14, 2006 - 10:50:56 AM
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  • HAL Id : tel-00079969, version 1



Alix Lombard. Les variations actuelles du niveau de la mer : Observations et causes.. Autre. Université Paul Sabatier - Toulouse III, 2005. Français. ⟨tel-00079969⟩



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