Articles | Volume 10, issue 1
Earth Syst. Sci. Data, 10, 281–301, 2018
Earth Syst. Sci. Data, 10, 281–301, 2018

Review article 12 Feb 2018

Review article | 12 Feb 2018

An improved and homogeneous altimeter sea level record from the ESA Climate Change Initiative

Jean-François Legeais1, Michaël Ablain1, Lionel Zawadzki1, Hao Zuo2, Johnny A. Johannessen3, Martin G. Scharffenberg4, Luciana Fenoglio-Marc5, M. Joana Fernandes6,7, Ole Baltazar Andersen8, Sergei Rudenko9,10, Paolo Cipollini11, Graham D. Quartly12, Marcello Passaro9, Anny Cazenave13,14, and Jérôme Benveniste15 Jean-François Legeais et al.
  • 1Collecte Localisation Satellite (CLS), 31520 Ramonville-Saint-Agne, France
  • 2European Centre for Medium-Range Weather Forecasts, Reading, UK
  • 3Nansen Environmental and Remote Sensing Center (NERSC), Bergen, Norway
  • 4University of Hamburg, Hamburg, Germany
  • 5University of Bonn, Bonn, Germany
  • 6Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal
  • 7Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR), 4450-208 Matosinhos, Portugal
  • 8DTU Space, 2800 Kongens Lyngby, Denmark
  • 9Deutsches Geodätisches Forschungsinstitut, Technische Universität München, 80333 Munich, Germany
  • 10Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
  • 11National Oceanography Centre, Southampton, SO14 3ZH, UK
  • 12Plymouth Marine Laboratory, Plymouth, PL1 3DH, UK
  • 13LEGOS, 31400 Toulouse, France
  • 14ISSI, Bern, Switzerland
  • 15ESA/ESRIN, 00044 Frascati, Italy

Abstract. Sea level is a very sensitive index of climate change since it integrates the impacts of ocean warming and ice mass loss from glaciers and the ice sheets. Sea level has been listed as an essential climate variable (ECV) by the Global Climate Observing System (GCOS). During the past 25 years, the sea level ECV has been measured from space by different altimetry missions that have provided global and regional observations of sea level variations. As part of the Climate Change Initiative (CCI) program of the European Space Agency (ESA) (established in 2010), the Sea Level project (SL_cci) aimed to provide an accurate and homogeneous long-term satellite-based sea level record. At the end of the first phase of the project (2010–2013), an initial version (v1.1) of the sea level ECV was made available to users (Ablain et al., 2015). During the second phase of the project (2014–2017), improved altimeter standards were selected to produce new sea level products (called SL_cci v2.0) based on nine altimeter missions for the period 1993–2015 (; Legeais and the ESA SL_cci team, 2016c). Corresponding orbit solutions, geophysical corrections and altimeter standards used in this v2.0 dataset are described in detail in Quartly et al. (2017). The present paper focuses on the description of the SL_cci v2.0 ECV and associated uncertainty and discusses how it has been validated. Various approaches have been used for the quality assessment such as internal validation, comparisons with sea level records from other groups and with in situ measurements, sea level budget closure analyses and comparisons with model outputs. Compared with the previous version of the sea level ECV, we show that use of improved geophysical corrections, careful bias reduction between missions and inclusion of new altimeter missions lead to improved sea level products with reduced uncertainties on different spatial and temporal scales. However, there is still room for improvement since the uncertainties remain larger than the GCOS requirements (GCOS, 2011). Perspectives on subsequent evolution are also discussed.

Short summary
Sea level is one of the best indicators of climate change and has been listed as one of the essential climate variables. Sea level measurements have been provided by satellite altimetry for 25 years, and the Climate Change Initiative (CCI) program of the European Space Agency has given the opportunity to provide a long-term, homogeneous and accurate sea level record. It will help scientists to better understand climate change and its variability.