Projecting regional sea-level changes for the 21 st century

Transcription

1 Projecting regional sea-level changes for the 21 st century Aimée Slangen Postdoctoral research fellow In collaboration with: Mark Carson (CEN Hamburg), Caroline Katsman (KNMI), Roderik van de Wal (IMAU), Armin Köhl (CEN Hamburg), Bert Vermeersen (NIOZ, TU Delft), Detlef Stammer (CEN Hamburg) CMAR

2 Introduction Sea level change: From global To regional What is happening at YOUR doorstep? WG1 SPM fig 9

3 Introduction Contributing processes to sea-level change: Land ice melt Ocean dynamics & density change Glacial isostatic adjustment [GIA] Terrestrial water storage change Atmospheric pressure loading Atmospheric pressure Can we model the regional patterns of these processes? What is the influence on projected regional sea-level changes?

4 Methodology Global climate models - CMIP5 21 AOGCM s Scenarios RCP4.5 ( o C) and RCP8.5 ( o C) T, P, SLP, global mean expansion, local sea-level anomalies [Mass change] Glaciers and ice caps [Mass change] Ice sheets [Mass change] Groundwater depletion [Volume change] Steric+dynamic [Volume change] Atmospheric loading [Solid earth deformation] Glacial Isostatic Adjustment Sea-level model gravitational effects Spatial patterns of sea-level change (period to )

5 Gravitational effect [Mass change] Ice Ocean 2200 km 6700 km

6 Land ice [Mass change] Glaciers, Ice caps & Ice sheet SMB (RCP4.5) Glaciers & Ice caps Volume-area approach with CMIP5 temperature and precipitation Ice sheet Surface Mass Balance SMB- T relation derived from AR4, use CMIP5 temperature change to determine SMB Ice sheet Dynamics e.g. calving, thinning & breaking of ice shelves Climate scenario independent Estimate is mean between IPCC AR4 (observed changes continue, no acceleration) and Katsman et al., 2011 (accelerated change) Glaciers, Ice caps & Ice sheet SMB (RCP8.5) Ice sheet Dynamics 0.15 ± 0.03 (GLAC) ± 0.03 (AIS) 0.03 ± 0.03 (GIS) 0.22 ± 0.04 (GLAC) ± 0.07 (AIS) 0.06 ± 0.06 (GIS) 0.09 ± 0.06 (AIS) 0.06 ± 0.05 (GIS) RSL change (m) (Figures by Marc Carson)

7 Terrestrial water storage [Mass change] Dam/reservoir building Expected to decrease in 21 st century (Chao, 2008) Groundwater depletion Groundwater depletion Expected to increase in 21 st century Decreasing surface water availability Decreasing groundwater recharge Increasing irrigation demand Projected using socio-economic scenarios and population change Currently only CMIP3-based available (Wada et al., 2012) 0.08 ± 0.01 m (Scenario independent) RSL change (m) (Figure by Marc Carson)

8 Glacial Isostatic Adjustment [Solid earth deformation] The Earth s viscous response to surface (un)loading Constant on study timescale (~100yr) Climate scenario independent ICE5G (Peltier, 2004) RSL change (m) (Figure by Marc Carson)

9 Steric+Dynamic & Atmospheric loading [Volume changes] Steric+Dynamic & Atm.loading (RCP4.5) Combines: 1. Density changes due to variations in Temperature Salinity 2. Ocean circulation changes 3. Atmospheric pressure changes (+1mb~-1cm) Steric+Dynamic & Atm.loading (RCP8.5) CMIP5 models Include exchange of heat (temperature changes), freshwater (precipitation) and momentum (wind change) Exclude freshwater forcing from land ice melt and associated gravitational effect 0.18 ± 0.05 m (RCP4.5) 0.27 ± 0.07 m (RCP8.5) RSL change (m) (Figures by Marc Carson)

10 CMIP5 Model differences 21 model ensemble Ensemble spread used to estimate uncertainty in steric+dynamic and land ice Large differences (amplitude, pattern), but also similarities (e.g. ACC dipole) (Figures by Marc Carson)

11 Uncertainties Land ice (a,b) CMIP5 21-ensemble & SMB- T uncertainties Ocean (c,d) CMIP5 21-ensemble Ice sheet dynamics (e) unbiased sd between lower and upper estimate Terrestrial (f) sd between 4 CMIP3 model outcomes GIA (g) absolute difference between 2 GIA models (Figures by Marc Carson)

12 Net projections & uncertainties (by 2100) Scenario A= 0.54 ± 0.32 m RCP4.5 + scenarioindependent terms (groundwater, ice dynamics &GIA) RSL change (m) Scenario B= 0.71 ± 0.48 m RCP8.5 + scenarioindependent terms (Figures by Marc Carson)

13 Regional deviations from the global mean Relative deviations +30% in Southern Ocean & around North America -50% in Arctic Ocean and around Antarctic Peninsula Absolute deviations Skewed distribution ~60% of surface > global mean Scenario A Scenario B

14 Regional differences (Scenario A) Land ice Steric+Dynamic GIA Groundwater Total

15 Discussion Land ice different studies use different estimates. Problem is: local information is needed to run sea-level model. Dynamical ice sheet contribution models needed Ice sheet SMB regional climate model runs for full CMIP5 ensemble GIA-model using other models yields (large) local differences Groundwater use full CMIP5 ensemble to drive hydrological model Ocean - ice sheet interaction incorporate freshwater forcing

16 Summary Goal Show you the most complete 21 st century regional sea-level projections using CMIP5 models Processes included Mass change (glaciers, ice sheets, groundwater) Volume change (steric+dynamic, atmospheric loading) Solid-earth deformation (GIA)

17 Conclusions Can we model the regional patterns of these processes? Yes, by combining different models we can show and study regional sea-level changes What is the influence of the different processes on projected regional sea-level changes? Each contribution can dominate locally in all climate scenarios Local deviations range from -50% to +30% wrt global mean Deviations >10% in ~30% of the ocean area Improving/constraining estimates of all contributions is important