Present-day variations of the mean sea level

Since the beginning of the 1990s. satellite altimetry has provided very pre cise measurements of present-day variations of the global mean sea level wi th a high spatio-temporal resolution and global coverage. Altimetry measure ments from the Topex-Poseidon satellite have reported a mean sea level rise of about 2 mm.yr(-1) since early 1993, which mostly results from thermal e xpansion of the ocean waters. Topex-Poseidon has also detected an annual va riation of the global mean sea level of about 4 mm amplitude, maximum in au tumn, which can be explained by the combined contributions of steric effect s and exchange of water with the atmosphere and continental water reservoir s. ((C) 1999 Academie des sciences/Editions scientifiques et medicales Else vier SAS.).