Day 4

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Paper title Is anthropogenic climate change detectable in multi-mission sea state altimeter products ?
  1. Antoine Hochet IFREMER Speaker
  2. Guillaume Dodet IFREMER
  3. Sevellec Florian
  4. Marie-Noëlle Bouin
  5. Fabrice Ardhuin LOPS - CNRS
Form of presentation Poster
  • A8. Ocean
    • A8.14 Remote-sensing of Ocean Waves and their Applications
Abstract text Sea state is a key component of the coupling between the ocean and the atmosphere, the coasts and the sea ice. Understanding how sea state responds to climate variability and how it affects the different compartments of the Earth System, is becoming more and more pressing in the context of increased greenhouse gas emission, accelerated sea level rise, sea ice melting, and growing coastline urbanization.

A new multi-mission altimeter product that integrates improved altimeter retracking and inter-calibration methods is being developed within the ESA Sea State Climate Change Initiative project. This effort will provide 30 years of uninterrupted records of global significant wave height. The 30 years represents the minimum duration required for computing climatological standards
following the World Meteorological Organization recommendation (WMO, 2015). In recent years, several
authors (e.g. Young et al., 2011; Young and Ribal, 2019; Timmermans et al., 2020) have computed the
trends in both the mean and extreme Hs using calibrated data from multi mission altimeter records. Whether these trends are the signature of anthropogenic climate change or the signature of natural variability is not known. Indeed, the atmosphere exhibits variability on a time scale comparable to the length of the satellite era and is therefore likely to hide the anthropogenic signal. Using the ECMWF ERA-5 reanalysis and focusing on North Atlantic region, we indeed show that the trends in winter-mean Hs computed over the satellite altimetry era are mostly associated with the atmospheric variability on the altimetry era time scale. Because the winter Hs variability in the North Atlantic is tightly linked with the overlying sea sevel pressure (SLP) winter variability, we extract the SLP modes of variability responsible for the altimetry era Hs winter trends in three regions (the Norwegian sea, the Mediterranean sea and the south of Newfoundland sea) where the Hs trends are significant.

In order to investigate the contribution of natural climate variability in these Hs trends, we analyzed SLP outputs obtained from the Community Earth System Model version 2 Large Ensemble (Lens2). Our analysis reveals that the magnitude of the SLP slope linked with internal variability becomes comparable to the magnitude of the slope linked with anthropogenic climate change for ~ 65 years of data i.e. around 2060, considering that 1992 (ERS-1 launch) is the beginning of the continuous altimetry era. This suggests that Hs modification associated with anthropogenic climate change of the atmospheric circulation will not be detectable in satellite altimetry trends before several decades.