Sea Level Rise SOEE3410: Lecture 15

Sea-level rise: implications Coastal Erosion Inundation of Land Increased Flood and Storm Damage Increased salinity of estuaries and aquifers ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Coastal erosion and accretion 1 cm rise in MSL erodes approx 1m horizontally of beach Sea level rise has a profound effect on rate of sedimentation Varying of sedimentation rates -> changing vegetation zones e.g. growth/shrinkage of marshes Storm surges force large quantities of shore-face sediments through inlets -> create tidal deltas/barriers 1m 0.1 Movement of sediment from tidal region to beneath near-shore waters Change to rate of sedimentation due to change in weight of overlying water column Wetlands/salt marshes – high tide water level regions e.g. mangrove ecosystems: provide natural protection against storm surges/hurricanes; sedimentary traps: stabilise coastlines; home to commercially exploited fish -in danger of being overcome by rising sea-levels (natural rate of mangrove rise:~2/3 mm yr-1) ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Vulnerable populated regions Large Coastal Cities: Populations >8 million (over 50% of US population live in coastal areas, >110 million) Highly populated Delta regions: Vulnerable to MSL rise http://www.survas.mdx.ac.uk ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics Flood and storm damage Coastal region more susceptible to storm surges, flooding, beach/coastal erosion => disruption of activities; danger to life; infrastructure damage 1 m rise in MSL would enable a 15-year storm to flood areas that today are only flooded by 100-year storms Urban flooding: contaminated water supply; drainage/waste systems overwhelmed Flood damages would increase 36-58% for a 30-cm rise in sea level, and increase 102-200% for sea level rise greater than 90 cm ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Increased salinity in estuaries Saltwater will penetrate farther inland and upstream in estuaries i.e. estuarine salt wedge. Higher salinity impairs both surface water and human groundwater water supply Saltwater intrusion would also harm ecosystems: aquatic plants and animals e.g. salt marshes, mangroves Higher salinity has been found to decrease seed germination Flooded agricultural land takes a long time to recover from saline water Decline of coastal commercial fisheries e.g. Salinity intrusion has already been cited as primary reason for reduced oyster harvests in Delaware and Chesapeake Bays in the USA ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level Not directly climate related: Tides – Periodic changes due to changing orbital motions of earth & moon Storm surges - Atmospheric effects inverse barometer, tropical storm/hurricane surges Wind-stress driven surge Directly climate related: Isostatic – Vertical movement of land Eustatic – changes of total sea water mass Steric – Thermal expansion of water volume ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level: astronomical tides ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level: atmospheric variations Inverse barometer effect The inverse response of sea level to changes in atmospheric pressure. A static reduction of 1.005 mb in atmospheric pressure will cause a stationary rise of 1 cm in sea level Low Atmospheric Pressure 980mb 1000mb 20cm ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level: storm surges A deep centre of low pressure situated over Scandinavia produces northerly winds Wind stress forces surface waters into the “bottle-neck” of the English Channel Flow is restricted by the Straits of Dover and sea levels rise along the adjacent coasts of East Anglia and the Netherlands 4. Other key ingredients include high Spring tides and on-shore winds  ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Glacial isostatic adjustment/PGR The weight applied to the crust is dispersed throughout the lithosphere The lithosphere is so rigid that the weight is transferred across the crust resulting in a peripheral depression and “forebulge” Around the periphery of the ice sheet margin up to a distance of 150-180 km, depression (>100m) occurs without ice loading This area can record relative sea level change without the complexity of glacial erosion or deposition The lateral displacement of mantle material from below the centre of ice sheet loading results in the formation of an area of slight uplift (10 - 20 m) beyond the peripheral depression (the forebulge). ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level: isostatic changes Isostatic changes = vertical land movements, Stockholm, Sweden (Glacial Isostatic Adjustment) Nezugaseki, Japan (abrupt jump in sea level record following earthquake in 1964) Fort Phrachula Bangkok, Thailand (sea level rise due to increased groundwater extraction since about 1960) Manila, Philippines (recent deposit from river discharges and reclamation works) Honolulu, Hawaii (a site in the PGR 'far field' without evident strong tectonic signals on timescales comparable to the length of the tide gauge record and with secular trend 1.5 mm/year). (courtesy of Proudman Oceanographic Lab) ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level: glacial isostatic adjustment/PGR Glacial Isostatic Adjustment (Post Glacial Rebound) i.e. melting of high latitude glaciers from 5000-15000 years BP (Proudman Oceanographic Labs) ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level rise: Eustatic changes Eustatic changes = volumetric (mass) changes Glaciers, ice-caps or ice-sheets: Gain mass by accumulation of snow (snowfall and deposition by wind-drift), which is gradually transformed to ice. Lose mass (ablation) mainly by melting at the surface or base with subsequent runoff or evaporation of the melt water Net accumulation occurs at higher altitude Net ablation at lower altitude The mass balance for an individual body of ice is usually expressed as the rate of change of the equivalent volume of liquid water, in m3/yr; the mass balance is zero for a steady state ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Factors affecting sea level rise: Steric rise As oceans warm, density decreases and thus even at constant mass the volume of the ocean increases Thermal expansion (or steric sea level rise) occurs at all ocean temperatures (albeit small in the deep ocean) Water at higher temperature or under greater pressure (at greater depth) expands more for a given heat input. Therefore, the global average expansion is affected by the distribution of heat within the ocean Salinity changes within the ocean also have a significant impact on the local density and thus local sea level, but have little effect on global average sea level change The rate of climate change depends strongly on the rate at which heat is removed from the ocean surface layers into the ocean interior – if heat is taken up more readily, climate change is retarded but sea level rises more rapidly ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics Measuring sea level ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Sea-level rise: Historic changes Past changes in sea level (From IPCC Analysis, 1998, 2001; Pugh, 2004) Since the Last Glacial Maximum (~20,000 years BP) MSL has risen by over 120 m at locations far from present and former ice sheets Between 15,000 and 6,000 years ago MSL rose rapidly at an average rate of 10 mm/yr. Following last glacial period local vertical land movements are still occurring today as a result of large transfers of mass from the ice sheets to the ocean During the last 6,000 years, global MSL variations on time-scales of a few hundred years and longer are likely to have been less than 0.3 to 0.5 m During the 20th century, tide gauge data shows MSL rises in the range 1.0 to 2.0 mm/yr (more than during 19th century) There is decadal variability in extreme sea levels but no evidence of widespread increases in extremes other than that associated with a change in the mean ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Evidence of recent sea-level rise Local trends in sea-level (i.e. relative to local land mass) ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Evidence of recent sea-level rise II ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Evidence of eustatic changes in sea-level Cumulative mass balance for three glaciers in different climatic regimes: Hintereisferner (Austrian Alps), Nigardsbreen (Norway), Tuyuksu (Tien Shan, Kazakhstan) IPCC, 2001 ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Evidence of eustatic changes in sea-level II Estimates of global sea level change over the last 140,000 years (continuous line) and contributions to this change from the major ice sheets: North America, including Laurentia, Cordilleran ice, and Greenland, (ii) Northern Europe (Fennoscandia), including the Barents region, (iii) Antarctica (From Lambeck, 1999) Source: IPCC, 2001 ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Sea level rise: contributing factors Δh (t) = X (t) + g (t) + G (t) + A (t) + I (t) + p (t) + s (t) The components of MSL rise are due to: X - thermal expansion (steric rise) g - loss of mass of glaciers and ice caps (eustatic rise) G - loss of mass of the Greenland ice sheet due to current climate change (eustatic rise) A - loss of mass of the Antarctic ice sheet due to current climate change (eustatic rise) I - loss of mass of the Greenland and Antarctic ice sheets due to the ongoing adjustment to past climate change (eustatic rise) p - runoff from thawing of permafrost (eustatic rise) s - deposition of sediment on the ocean floor ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Contributing factors: permafrost Permafrost occupies 25% of land area in the northern hemisphere Estimates of ice volume in northern hemisphere permafrost 1.1 - 3.7  1013 m3 ( 0.03 to 0.10 m of global-average sea level) The active layer (shown in grey) thaws each summer and freezes each winter, while the permafrost layer remains below 0°C. ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Possible climate induced changes: permafrost Characteristics that could change: Area of permafrost Thickening of the active layer (layer of seasonally thawed ground above permafrost) Guestimated Effects (IPCC) Assuming:  permafrost vol   permafrost area; present warming trends 50% conversion of permafrost melt available to direct runoff into ocean Then: Contribution to MSL - 1990 to 2100 is 0 to 25 mm (0 to 0.23 mm/yr) as compared to - 20th century: 0 to 5 mm (0 to 0.05 mm/yr) ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

MSL: predicted changes IPCC, 2001: Global average sea level changes from thermal expansion AOGCM experiments with observed concentrations of GHGs in 20th century; then, following IS92a scenario for 21st century; (including the direct effect of sulphate aerosols) shaded region shows the bounds of uncertainty associated with land ice changes, permafrost changes and sediment deposition for the groups of models showing largest/smallest sea level change Estimated rate of Mean Sea Level (MSL) rise: 5  2-9 mm/yr i.e. 2 – 5 times the rate experienced over the past century ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

The major climate-related contributing factor to sea level rise is … IPCC: Identified 1.5-2.0 mm yr-1 rise during 20th century Main factor was rising surface T => steric contribution But … Levitus et al (2000): identified increased heat storage in oceans -> data suggests steric contribution is only 0.5 mm/yr Where is the rest of the 1.5-2.0 mm yr-1 rise from? IPCC estimate only 0.2 mm/yr for eustatic (volumetric) MSL rise i.e. So … Does this mean that the IPCC estimates are actually wrong? steric (hsteric) height + (heustatic) = 0.5 + 0.2 = 0.7 mm/yr ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

The major climate-related contributing factor to sea level rise is … Total Eustatic Temperature Salinity The time series are spatially averaged (50ºS to 65ºN), 5-year running means computed for the upper 3000 m of the ocean Ocean Freshening, Sea Level Rising, Walter Munk, Science 27 June 2003 300: 2041-2043 ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

The major climate-related contributing factor to sea level rise is … Eustatic or steric? Mean salinity of the global ocean has decreased slightly between 1954 - 1997, implying the addition of fresh water mass to oceans => combined steric rise due to temperature and salinity hsteric = hT + hS = 0.5 +0.05 = 0.55 mm/year If source of freshening is melting ice sheets and changes in continental water storage, there must be a eustatic contribution But, it must not be counted twice i.e. as both steric and eustatic! Consider 3 modes of ocean freshening: Regions where T and S steric effects cancel i.e. no density change => no MSL Melting of floating ice: will freshen ocean but cause no MSL rise (Archimedes) => only steric rise 3. Freshwater import from continents => eustatic AND steric rise Ocean Freshening, Sea Level Rising, Walter Munk, Science 27 June 2003 300: 2041-2043 ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

The major climate-related contributing factor to sea level rise is … Ocean Freshening, Sea Level Rising, Walter Munk, Science 27 June 2003 300: 2041-2043  = 1028 kg/m3  = 28 kg/m3 hs = 0.05 mm/yr Salinity induced rise: heustatic = (/)hs = 36.7 hs= 1.8 mm/yr Assuming global ocean covers an area of 3.6 108 km2 This eustatic change would require an ice melt volume of 650 km3/year ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

The major climate-related contributing factor to sea level rise is … Ocean Freshening, Sea Level Rising, Walter Munk, Science 27 June 2003 300: 2041-2043 Sea ice covers: an area of 107 km2  30% seasonal changes; ~ 3m thick Total volume 30,000 km3; seasonality reduces this volume by 0.3% or 90 km3/yr Estimation of sea ice thinning of approximately 4 % over the last 20 years  60 km3/yr a total loss of sea ice per year 150 km3/yr  135 km3/yr of freshwater input i.e. purely steric contribution to sea level change => Readjust eustatic rise estimate: heustatic = 650 km3/year- 135 km3/yr = 515 km3/yr or 1.4 mm/yr heustatic + hsteric = 1.4 + 0.5 = 1.9 mm/yr Value is within range of IPCC estimate! Munk: Probably not the solution but gives insight to problem! ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Future improvements to observational methods GPS is being used to fix the position of tide gauge bench marks to an accuracy  10 mm Will allow local MSL to be corrected for all local land movement Allow decoupling of earth movement from tide gauge measurements Buddy checking – compare records of MSL between different localities (~ few 100 km) ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics

Summary - sea level rise Sea Level Rise has massive global implications on the natural world and human society Major climate-related causes of sea level rise: Isostatic - PGR Eustatic – Volumetric Steric – Temperature Interaction of processes still not well understood Global estimates of MSL will improve as satellite and GPS database and time series increases ENVI3410 : Coupled Ocean & Atmosphere Climate Dynamics