Regional sea level rise – a multitude of contributions, effects, and interactions Remote Sensing of Ocean Circulation and Environmental Mass Changes (REOCIRC), UNIS & NERSC NERSC, BCCR SEALEV, coordinating, learning, fascinating Future efforts to improve local projections, into useful projections for coastal management. Jan Even Øie Nilsen

Many processes affect sea level Milne et al. (2009)

Outline + 4 3 2 3 1 IPCC, 2013 Three time scales to study: - Past geological times can tell us about bounds and possible rates of change. (Not today.) 1

Global mean sea level GMSL

GMSL - observations Measured sea level Mass change Thermal expansion Budget is reasonably closed Mass change Figure 13.6: Global mean sea level from altimetry from 2005 to 2012 (blue line). Ocean mass changes are shown in green (as measured by GRACE) and thermosteric sea level changes (as measured by Argo) are shown in red. The black line shows the sum of the ocean mass and thermosteric contributions (updated from Boening et al. (2012)). Thermal expansion

Observed contributions to GMSL The relative importance of the individual contributions is subject to changes. 1.1 0.85 .3 .25 .35 3.2 mm/yr Jonathan Gregory Lead author Ch.13 Sea Level Change

(different emission scenarios) (global mean sea level rise) (different emission scenarios) AR5 - Projections 80 cm Representative concentration pathways: RCP8.5 ikke stabilisering før 2100 (et slags business as usual scenario) RCP4.5 middels-lav, reduksjon rundt 2050 RCP2.6 reduksjon allerede 2020 og negativ CO2 utslipp før 2100 (optimistisk) 30 cm Jonathan Gregory Lead author Ch.13 Sea Level Change

0.47 m Components, but still only onto the global mean. Jonathan Gregory Lead author Ch.13 Sea Level Change

Regional sea level

The sea surface … is not flat! Mean Sea Surface CLS01 The altimeter provides the sea surface height relative to the reference ellipsoid. It is the sum of the geoid plus the dynamic topography, once removed other oceanic and atmospheric effects. By averaging altimetric heights over a given period, a Mean Sea Surface (MSS) can be estimated. The MSS is referenced to the Earth ellipsoid; we use CLS01 MSS, computed using altimeter data averaged over the 1993-1999 period. 200 m equals 6 micrometers on a globe of 20 cm radius. Mean Sea Surface CLS01 … is not flat!

Observed sea level trends, by satellites (Oct 1992 - Jan 2008) Sea level rise Observed sea level trends, by satellites (Oct 1992 - Jan 2008) Actual change: Even sinking in some areas. Due to natural fluctuations in temperature distribution in the oceans and changes in ocean circulation, and gravity changes. N: 5 mm/yr (Botn. 17 mm/yr) … is not uniform! Cazenave et al. (2008)

Contributions to and distribution of relative sea level rise Mass exchange Land ice melt Hydrological changes Gravity changes “Thermal expansion”, i.e., steric height Heat uptake / freshwater input (Changed) circulation Deep water expansion => shelf mass loading Weather effects Surface air pressure Surface wind stress Storm surges Vertical land motion

Mass exchange

and shrinking glaciers in the world Number of growing and shrinking glaciers in the world 1905 1925 1945 1965 1985 ´05 New Guinea World Global Monitoring Service (2008) Africa New Zealand Scandinavia Central Europe South America Fleste breer minker de fleste steder (alle). Northern Asia Antarctica Central Asia North America Arctic Worldwide

Mass exchange from ice sheets Greenland: 100 Gt/yr of ice loss is equivalent to about 0.28 mm/yr of global mean sea level rise. Antarctica: Velicogna, 2009

Fingerprinting – a gravitational effect Land ice melts. Gravity is reduced. Sea water moves away and nearer sea level sinks (large scale). Solid earth rises (more local effect), which affects relative sea level. (Tamisiea et al., 2003)

From ice melt to regional sea level: Fingerprinting For Spitsbergen: Greenland × -0.1 Antarctica × 1.1 Glaciers × -0.1 Greenland melts Antarctica melts (Tamisiea et al., 2001, 2003)

Mass exchange and gravity changes From ice melt to regional sea level: Mass exchange and gravity changes Continental ice Land hydrology Estimates. Total fingerprint GRACE 2003-2009 Riva et al (2010)

From ice melt to regional sea level: Circulation changes In addition to the mass input, freshwater input leads to circulation changes which redistributes SSH. A “hybrid” mass input -> steric change -> circulation change Stammer et al (2008) MIT-OGCM; Greenland input (Mass input corresponding to ≈ 4 mm/yr eustatic SLR).

Steric height changes “thermal expansion”

Opposite for increasing salinity. Thermal expansion Colder = less movement Need less space Need more space Warmer = more movement SKULLE HATT FORKLARING PÅ HALIN KONTRAKSJON OGSÅ. Opposite for increasing salinity.

The effect of thermal expansion (and fresh water content) The water is expanding, but still the same ‘amount’ of water at each location. NorESM 2010-2095: Fremtid, for modellene kan separere effektene, det er ikke mulig i obs. Og for å peke litt til fremskrivninene. Mengde = Masse, antall molekyler. Richter et al (2013)

Expansion at depth pushes water onto shallower regions Shelf mass loading Expansion at depth pushes water onto shallower regions This is mass exchange, not to be confused with local thermal expansion! Change in mass of water NorESM 2010-2095: Expansion deeper than 700 m Dypere enn 700 m A “hybrid”: Steric change -> mass redistribution Richter et al (2013)

Weather effects Flytte? Nei, det har ikke så mye med sterisk å gjøre.

Weather effect – air pressure Inverse barometer effect (IBE):

Weather effect – wind stress Large scale circulation Atlantic inflow (both dynamic and steric changes) North Sea inflow Storm surges Local onto coast Short term In combination with low pressure (IBE)

Vertical land motion Stepping onto land Many places the uncertainties in land uplift are as large as the sea level rise. Stepping onto land

Vertical land motion is: Rebound from ice melt Elastic crust rebounding “immediate” Present day ice melt Viscoelastic mantle mass flow slow (several 1000s of years) Glacial isostatic adjustment (GIA) Tectonic plate activity Ground depletion related subsidence Previous, today’s and future mass variations in ice sheets and glaciers Viscoelastic also relevant from recent changes in the mass load.

Vertical motion of Scandinavia Mainly GIA: Glacial isostatic adjustment from the Fenno-scandian ice sheet of the latest ice age. 9 mm/yr 0 mm/yr Ekman (1996);

Vertical motion of Spitsbergen 6.6 6.9 8.6 9.3 6.0 7.3 -0.8 5.0 Source: Norwegian Map Authority Uplift in mm/yr Not to mention the local gravity effects. Also tectonics from mid Atlantic ridge Large spatial differences Interannual variability of ~1 mm/yr Present day local ice mass changes GIA-part is ~1.6 mm/yr

Relative sea level in Spitsbergen PSMSL CGPS Land uplift Ny-Ålesund Continuous GPS receivers (CGPS) Permanent Service for Mean Sea Level (PSMSL)

The three sea levels SSH rise Observed sinking No SSH change TIDE GAUGES GMSL SSH rise Observed sinking The three sea levels 1993–2012 No SSH change No observed change All ocean related effects, in sum is what altimeters see (SSH). Non uniform rise Land uplift comes into play FAQ13.1, Figure 1: Map of rates of change in sea surface height (geocentric sea level) for the period 1993–2012 from satellite altimetry. Also shown are relative sea level changes (grey lines) from selected tide gauge stations for the period 1950–2012. For comparison, an estimate of global mean sea level change is also shown (red lines) with each tide gauge time series. The relatively large, short-term oscillations in local sea level (grey lines) are due to the natural climate variability described in the main text. For example, the large, regular deviations at Pago Pago are associated with the El Niño-Southern Oscillation. 1. Global mean sea level GMSL 2. Sea surface height SSH 3. Relative RSL IPCC AR5

Summary: The future projections Global patterns and for Spitsbergen CMIP5 RCP4.5 Change between 1986–2005 to 2081–2100 “rise by the end of the 21st century” Relative sea level (RSL)

Projected mass contributions to RSL from ice sheets Figure 13.18: Ensemble mean regional contributions to sea level change (m) from (a) GIA, (b) glaciers and (c) ice sheet SMB. Panels (b) and (c) are based on information available from scenario RCP4.5. All panels represent changes between the periods 1986–2000 and 2081–2100.

Projected mass contributions to RSL from glaciers Figure 13.18: Ensemble mean regional contributions to sea level change (m) from (a) GIA, (b) glaciers and (c) ice sheet SMB. Panels (b) and (c) are based on information available from scenario RCP4.5. All panels represent changes between the periods 1986–2000 and 2081–2100.

Projected contribution from GIA to RSL Figure 13.18: Ensemble mean regional contributions to sea level change (m) from (a) GIA, (b) glaciers and (c) ice sheet SMB. Panels (b) and (c) are based on information available from scenario RCP4.5. All panels represent changes between the periods 1986–2000 and 2081–2100.

Projected steric height changes Figure 13.16: (a) Ensemble mean projection of the time-averaged dynamic and steric sea level changes for the period 2081–2100 relative to the reference period 1986–2005, computed from 21 CMIP5 climate models (in m), using the RCP4.5 experiment. The figure includes the globally averaged steric sea level increase of 0.18 ± 0.05 m. (b) RMS spread (deviation) of the individual model result around the ensemble mean (m). with dynamic changes

Projected atmospheric pressure loading Figure 13.17: Projected ensemble mean sea level change (m) due to changes in atmospheric pressure loading over the period from 1986–2005 to 2081–2100 for (a) RCP4.5 and (b) RCP8.5 (contour interval is 0.01 m). Standard deviation of the model ensemble due to the atmospheric pressure loading for (c) RCP4.5 and (d) RCP8.5 (contour interval is 0.005 m).

Regional sea level rise by the end of the 21st century Fig. 13.20b GMSLR=0.47 m (Not relevant? Is net vertical coastal land uplift zero? Not necessarily.) Figure 13.20: Ensemble mean net regional sea level change (m) evaluated from 21 CMIP5 models for the RCP scenarios (a) 2.6, (b) 4.5, (c) 6.0 and (d) 8.5 between 1986–2005 and 2081–2100. Each map includes effects of atmospheric loading, plus land-ice, GIA and terrestrial water sources. Very likely that sea level will rise in more than 95% of the ocean area. About 70% of the coastlines worldwide are projected to experience sea level change within 20% of the global mean.

Some locations’ projected relative sea level rise (by eyeballing) [cm] Contributing factor Spits-bergen Stockholm Bergen SW-UK Cochin (India) Mass from ice sheets -2 10 8 19 Mass from glaciers -16 9 15 GIA -15 -10 6 Steric height 20 27 25 22 23 Atmospheric pressure 1 -0.5 -0.7 -0.4 Total estimated 3 31 30.5 43.3 55 Map Projection <10 30 40 to 50 Remember: This is only for the mean of the RCP4.5 emission scenario!

Spitsbergen RSL Mass from Ice sheets Mass from glaciers GIA from eyeballing Mass from Ice sheets Mass from glaciers GIA Steric height Global SLR: 0.47 m. AR5 RSL-rise: 0 cm Map projection Spitsbergen: 90% CL uncertainty bound (p = 0.05) Atmospheric pressure 0.54 m Total estimated Map projection

Regional sea level rise by the end of the 21st century - all scenarios “Very likely that sea level will rise in more than 95% of the ocean area.” “About 70% of the coastlines worldwide are projected to experience sea level change within 20% of the global mean.” Figure 13.20: Ensemble mean net regional sea level change (m) evaluated from 21 CMIP5 models for the RCP scenarios (a) 2.6, (b) 4.5, (c) 6.0 and (d) 8.5 between 1986–2005 and 2081–2100. Each map includes effects of atmospheric loading, plus land-ice, GIA and terrestrial water sources.