Impact Analysis of Global Warming on Wet Path Delay Over the Satellite Altimetry Era (1993–2022)

Thirty years of satellite radar altimetry allow the monitoring of sea-level changes at a global scale. The accurate determination of these changes relies directly on how accurately the wet path delay (WPD) in the altimeter observations, mostly due to tropospheric water vapor (WV) content, is estimated. The Clausius–Clapeyron (CC) relation predicts a 7% rise in atmospheric WV for every 1 °C of warming. Building upon this relationship, this study analyzes the impact of global warming on WPD over the satellite altimetry record (1993–2022). Near surface temperature (T2m) and total column water vapor (TCWV) provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ReAnalysis 5 (ERA5) have been analyzed. Results reveal that global land-ocean temperature has increased at an average rate of 0.23 °C/decade and, in close association, TCWV has increased at a rate of 0.37 mm/decade. For the global ocean, these trends are 0.18 °C and 0.43 mm per decade, respectively. This shows that, per 1 °C of warming, TCWV increases at an average rate of 7% globally (CC relation) and 9% over the global ocean, with respect to its global mean for the study period. Global warming over these 30 years has been responsible for an average increase in TCWV of 1.3 mm over oceans, representing an increase of 8 mm in WPD (0.26 mm/year), equivalent to 1.4 cm (9%) per 1 °C of warming. This study brings crucial findings on the impact of global warming in satellite altimetry, addressing, in particular, physical signals that should not be misled with drifts.