Global mean sea level variations are computed from TOPEX/POSEIDON (cycles 11 - 364) altimetry (Nerem et al.,1994). Each asterisk represents a 10 day estimate of the global mean sea level variation with respect to the 1993 - 1999 average. The solid black line is a smoothed estimate employing a 60-day Hanning filter. The red line is the Reynolds' sea surface temperature variations with the annual cycle removed. The dark blue asterisks represent the transition from TOPEX ALT A to ALT B. Several instrument drifts and biases are accounted for in deriving the trend in mean sea level over the nine year period. Comparison of the Pathfinder sea surface height time series against a global network of tide gauges (analysis performed by Gary Mitchum) shows residual drift. If this drift is applied to the altimetric time series the resultant MSL estimate is 2.6 mm/year. Detection and validation of these trends is a field of active research.