Is coastal mean sea level rising faster than the global mean? A comparison between tide gauges and satellite altimetry over 1993-2007

Based on a careful selection of tide gauges records from the Global Sea Level Observing System network, we investigate whether coastal mean sea level is rising faster than the global mean derived from satellite altimetry over the January 1993-December 2007 time span. Over this 15-year time span, mean coastal rate of sea level rise is found to be +3.3 +/- 0.5 mm/yr, in good agreement with the altimetry-derived rate of +3.4 +/- 0.1 mm/yr. Tests indicate that the trends are statistically significant, hence coastal sea level does not rise faster than the global mean. Although trends agree well, tide gauges-based mean sea level exhibits much larger interannual variability than altimetry-based global mean. Interannual variability in coastal sea level appears related to the regional variability in sea level rates reported by satellite altimetry. When global mean sea level is considered (as allowed by satellite altimetry coverage), interannual variability is largely smoothed out.