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Sea Level, an Essential Climate Variable and an integrator of climate change, A. Cazenave


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A. Cazenave (CNES, Toulouse, France), M. Ablain, (CLS, Ramonville St Agne, France), J.-F. Legeais (CLS, Ramonville St Agne, France), B. Meyssignac (CNES, Toulouse, France)

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Sea Level, an Essential Climate Variable and an integrator of climate change, A. Cazenave

  1. 1. Sea Level: An Essential Climate Variable and an indicator of Climate Change A. Cazenave, B. Meyssignac LEGOS-CNES M. Ablain, G. Larnicol, J.F. Legeais CLS
  2. 2. Hydrosphere CLIMATE Human activities The climate system Cryosphere Biosphere Atmosphere Land surfaces
  3. 3. 3 Global Climate Observing System/GCOS, 2011 (WMO, IOC, UNEP, ICSU) 50 Essential Climate Variables (ECVs)  26 observable from space Climate component Space-based ECVs Atmosphere • Surface  • Altitude  • Atmospheric Composition • Temperature, precipitation, humidity,pression, surface fluxes, wind • Radiative budget at TOA, temperature, water vapour, clouds • CO2, CH4, etc., ozone, aerosols Ocean • Surface  • Sub surface  •Sea surface temperature, sea urface salinity, sea level, sea state, sea ice, currents, waves, biological activity (ocean colour) , carbon dioxide partial pressure •T, S, currents, ocean tracers, carbon, phytoplankton Land surfaces  Soil moisture, ground waters, lake level, snow pack, glaciers, ice sheets Albedo, land use & land use change, vegetation, LAI & other vegetation indices, biomass, fires
  4. 4. 6 «Grand Challenges » in climate research defined by the WCRP World Climate Research Programme (World Meteorological Organization) 1. Clouds, atmospheric circulation and climate sensitivity 2. The cryosphere in a changing climate 3. Climate extremes 4. Sea level rise and coastal impacts 5. Changes in water availability 6. Regional climate information
  5. 5. The ESA Climate Change Initiative (CCI) • Develop and validate algorithms to meet GCOS ECV requirements for (consistent, stable, error-characterized) global satellite data products from multi- sensor data archives • Produce and validate, within an R&D context, the most complete and consistent possible time series of multi-sensor global satellite data products for climate research and modelling • Optimize the impact of ESA EO missions data on climate data records • Generate complete specifications for an operational production system • Strengthen inter-disciplinary cooperation between international earth observation, climate research and modelling communities, in pursuit of scientific excellence.
  6. 6. 13 CCI ECVs, 14 projects
  7. 7. Why is it important to precisely monitor sea level changes? 1. Global mean sea level rise is an integrator of changes occuring in the climate system  provides an integrative view of currents changes (land ice melt, ocean warming); good indicator of climate change 2. Studying the sea level budget using different observing systems offers constraints on « missing contributions » (e.g. deep ocean warming) or poorly known components (e.g., ground water depletion in aquifers); also allows cross- validation of other ECVs (e.g., glaciers, ice sheets) 3. Observed sea level changes at global and regional scale help validating climate models used for projections 4. Observed sea level variations at the coast provide constraints on models of coastal impacts and shoreline erosion
  8. 8. Global mean sea level evolution (1993-2015) Rate of sea level rise (1993-2015) 3.3 +/- 0.4 mm/yr Land waters Source : LEGOS
  9. 9. 9 Tide gauges 1.7 +/- 0.3 mm/yr 20th Century Altimeter satellites Observed global mean sea level rise since 1900 3.3 +/- 0.4 mm/yr since 1993 Source : LEGOS
  10. 10. Earth’s Energy Budget Energy in Energy in Energy outEnergy out Net balance Net positive imbalance Today  Energy imbalance  0.5 -1 Wm-2 Equilibrium Sun Sun Earth Earth
  11. 11. The ocean heat content is increasing IPCC AR5 Ocean heat content = Ocean mass X Heat capacity of water X Ocean mean temperature change
  12. 12. 12 Heat content (1022 Joules) 5 10 15 Ocean (93.4%) Atmosphere 2.3 % Land 2.1% Heat storage in the climate system (Last 50 years) 93% of anthropogenic heat accumulated in the climate system over the last 50 years are stored in the ocean Ice melting 2.1 % IPCC AR5
  13. 13. Ice mass loss from Greenland and Antarctica measured by space techniques since 1990 (in Gt)  mass loss acceleration during the last decade Antarctica + Greenland Antarctica Greenland Shepherd et al., 2012 IPCC AR5 Greenland Antarctica
  14. 14. ΔMocean = - ΔMLI - ΔMLW - ΔMWV - ΔM -……. Observed Global Mean Sea Level Rise = Ocean Thermal Expansion + Ocean Mass increase Land waters Atmospheric water vapor Ocean mass Land ice Δ = Time variation M = Masse LI = Land Ice (glaciers + ice sheets) LW= Land Waters WV= Water Vapour Snow Snow
  15. 15. 35% Ocean warming Thermal Exp Land Ice Land Waters 42% 12% Causes of the global mean sea level rise (altimetry era: last 2 decades) Individual contributions (in % of the observed rate of rise) Land ice melt IPCC AR5 Land waters
  16. 16. Sum Contrib. Observed Residual 2.8 +/- 0.5 mm/yr 3.2 +/- 0.4 mm/yr 0.4 mm/yr residual Sum of contributions Rate of rise IPCC AR5 results on the 1993-2010 sea level budget Observed 16 12%
  17. 17. 17 Causes of the global mean sea level rise - Ocean warming (thermal expansion) - Land ice melt (glaciers + ice sheets) - Exchange of water with continental reservoirs (ground water pumping) Deep ocean warming
  18. 18. 18 Since ~ 2003/05, Argo + GRACE  steric sea level (upper ocean) + ocean mass Antarctique Argo Thermal expansion + salinity of the upper ocean (0-2000 m) mass changes ocean mass glaciers, ice sheets, land waters
  19. 19. Source: Dieng et al., 2015 Ocean Mass from GRACE Thermal Expansion (Argo-based T/S  2000m) Black : Altimetry-based Global Mean Sea Level Red: Sum of Thermal Exp.+ Mass Observed Global Mean Sea Level = Thermal Expansion + Ocean Mass
  20. 20. IPCC-AR5 projections of Global Mean Sea Level Rise during the 21st century under two warming scenarios Sea Level Rise Pessimistic scenario (RCP 8.5) Optimistic scenario (RCP 2.6) 50 cm-100 cm
  21. 21. 21 Sea level rise is not uniform! Rates of sea level rise observed by satellite altimetry over 1993-2014 source: LEGOS
  22. 22. Ensemble mean projections of regional sea level rise by the end of the 21st century (regional variability due to non uniform thermal expansion & salinity + solid Earth effects/deformations of ocean basins ) metres Global mean sea level rise of 75 cm (high warming scenario) IPCC AR5
  23. 23. Sea level rise in Western Europe in 2100 simulated by 2 French climate models RCP8.5 scenario (global mean sea level rise = 75 cm) cm Institut Pierre Simon Laplace MétéoFrance cm
  24. 24. Expected coastal impacts of future sea level rise: - Stronger temporary flooding during extreme events - Permanent flooding in low coastal areas - Shoreline erosion - Shoreline retreat - Salt intrusion in coastal aquifers and estuaries - Damages on coastal defences - Negative impacts on coastal biodiversity - …….
  25. 25. Temporary flooding at Palavas-les-flots (Mediterranean coast) for + 35cm and +1m sea level rise (stormy conditions identical to the 1982 storm) m +35cm+1m Source : BRGM; from R. Pedreros, S. Lecacheux & C. Vinchon
  26. 26. ECVs implemented by the CCI
  27. 27. Hydrosphere CLIMATE Human activities The climate system Cryosphere Biosphere Atmosphere Land surfaces Thanks for your attention!