1. 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

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

3. 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

4. Global mean sea level
GMSL

5. 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

6. 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

7. (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

8. 0.47 m Components, but still only onto the global mean.
Jonathan Gregory
Lead author
Ch.13 Sea Level Change

9. Regional sea level

10. 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 period.
200 m equals 6 micrometers on a globe of 20 cm radius.
Mean Sea Surface CLS01
… is not flat!

11. Observed sea level trends, by satellites (Oct 1992 - Jan 2008)
Sea level rise
Observed sea level trends, by satellites (Oct 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)

12. 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

13. Mass exchange

14. 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

15. 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

16. 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)

17. 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)

18. 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
Riva et al (2010)

19. 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).

20. Steric height changes
“thermal expansion”

21. 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.

22. The effect of thermal expansion (and fresh water content)
The water is expanding, but still the same ‘amount’ of water at each location.
NorESM :
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)

23. 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 :
Expansion deeper than
700 m
Dypere enn 700 m
A “hybrid”: Steric change -> mass redistribution
Richter et al (2013)

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

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

26. 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)

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

28. 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.

29. 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);

30. 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

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

32. 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

33. 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)

34. 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.

35. 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.

36. 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.

37. 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

38. 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 m).

39. Regional sea level rise by the end of the 21st century
Fig b
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.

40. 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!

41. 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

42. 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.