????- Global warming and Sea Level Rise

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Lecture 7 ????- Global warming and Sea Level
Rise
http//flood.firetree.net
CU SLR interactive wizard
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Are you knowledgeable about SLR ? Quiz
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Sea-level rise implications/consequences

• Coastal Erosion
• Inundation of Land
• Increased Flood and Storm Damage
• Increased salinity of estuaries and aquifers

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Cliff erosion
suspect?
Source Tyndall Centre for Climate Change Research
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Coastal erosion and accretion

• 1 cm rise in MSL erodes approx 1m horizontally
  of beach
• SLR has a profound effect on the rate of
  sedimentation
• Varying of sedimentation rates -gt changing
  vegetation zones e.g. growth/shrinkage of
  marshes (high tide water level regions)
• Storm surges force large quantities of shore-face
  sediments through inlets -gt create tidal
  deltas/barriers

1m
0.01
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Bruun Rule (Only describes one of the processes
affecting sandy beaches)

• R G(L/H)S
• H B h
• R shoreline recession due to a sea-level rise S
• h depth at the offshore boundary
• B appropriate land elevation
• L active profile width between boundaries
• G inverse of the overfill ratio

Source Nicholls, 1998
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Vulnerable coastal/island regions
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Vulnerable populated regions
Mega Coastal Cities Populations gt8 million (over
50 of US population (110 million) live in
coastal areas Highly populated Delta regions
http//www.survas.mdx.ac.uk
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Flood and storm damage

• Coastal region more susceptible to storm surges,
  flooding, beach/coastal erosion
• gt 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 102-200 for a 90-cm rise

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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
  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
• 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

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Factors affecting sea surface high (SSH)

• Not directly climate related
• Tides Periodic changes due to changing orbital
  motions of earth moon
• Storm surges - Atmospheric effects
• inverted barometer, tropical storm/hurricane
  surges
• Wind-stress driven surge

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astronomical tides
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Inverted barometer (IB) effect
The inverse response of sea level to changes in
atmospheric pressure gt A static reduction of
1-mb in atmospheric pressure will cause a
stationary rise of 1-cm in sea level
980mb
1000mb
20cm
Lower Atmospheric Pressure
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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 

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The Thames Barrier
the major part of the tidal defenses protecting
London
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Factors affecting sea surface high (SSH)

• Directly climate related
• Isostatic Vertical movement of land
• Eustatic changes of total sea water mass
• Steric Thermal expansion of water volume

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Glacial/interglacial isostatic adjustment(PGR
Post Glacial Rebound)

• 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 (gt100m)
  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).

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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 '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)
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Glacial isostatic adjustment/PGR
Glacial Isostatic Adjustment (Post Glacial
Rebound) i.e. melting of high latitude glaciers
from 5,000-15,000 years BP
(Proudman Oceanographic Labs)
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Eustatic changes volumetric (mass) changes

• In 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

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Examples of eustatic changes
Cumulative mass balance for three glaciers in
different climatic regimes Hintereisferner
(Austrian Alps), Nigardsbreen (Norway), Tuyuksu
(Tien Shan, Kazakhstan) IPCC, 2001
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Nigardsbreen glacier in Norway
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Nigardsbreen glacier
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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 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

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Measuring sea surface height
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Sea-level rise Historic changes

• Since the Last Glacial Maximum (20,000 years BP)
  MSL has risen by over 120 m
• 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 (larger
  as compared to 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

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Estimates of global sea level change over the
last 140,000 years (continuous line)

• Contributions from the major ice sheets
• North America, including Laurentia, Cordilleran
  ice, and Greenland,
• (ii) Northern Europe (Fennoscandia), including
  the Barents region,
• (iii) Antarctica (Lambeck, 1999) Source IPCC,
  2001

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Recent sea-level rise
Local trends in sea-level (i.e. relative to local
land mass)
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Recent Sea-Level Rise in South Pacific
(1991-2004)
Relative net sea-level trend (in mm/year) after
subtracting the effects of PGR and the IB
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Recent sea-level rise Global trend
Source http//ilrs.gsfc.nasa.gov/
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Contributing factors to Sea Level Rise
?h (t) X (t) g (t) G (t) A (t) I (t)
p (t) s (t) 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
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Thawing of permafrost

• Permafrost occupies 25 of land area in the N.H.
• Estimates of ice volume in N.H. 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 0C.
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Characteristics of permafrost that could change
under G.W.

• Increasing of thawing area (horizontally)
• Thickening of active layer (vertically)
• Effects (IPCC TAR)
• Assuming
• ? permafrost vol ? ? permafrost area
• current warming trend continues
• 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)

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Debating the major contributing factor to sea
level rise
IPCC Identified 1.5-2.0 mm yr-1 rise during
20th century Main factor rising surface T gt
steric contribution But Levitus et al (2000)
identified increased heat storage in oceans -gt
data suggests steric contribution is only 0.5
mm/yr IPCC estimate only 0.2 mm/yr for eustatic
(volumetric) MSL rise, i.e. So Where is
the rest of the 1.5-2.0 mm yr-1 rise from?
?hsteric ?heustatic 0.5 0.2 0.7 mm/yr
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Debating the major contributing factor to sea
level rise
Total
Eustatic
Steric
Salinity
The time series are spatially averaged (50ºS to
65ºN), 5-year running means computed for the
upper 3000 m of the ocean
Source Ocean Freshening, Sea Level Rising,
Walter Munk, Science 27 June 2003 300 2041-2043
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• Eustatic or steric?
• Mean salinity of the global ocean has decreased,
  implying the addition of fresh water mass to
  oceans
• gt combined steric (due to temperature rise) and
  salinity effects
• ?hsteric ?hT ?hS 0.5 0.05
  0.55 mm/year
• If source of freshening is due to changes in
  continental water storage, there must be an
  eustatic contribution
• But, it can NOT be counted twice as both steric
  and eustatic!
• Consider 3 modes of ocean freshening
• Regions where T and S steric effects cancel i.e.
  no density change gt no ?MSL
• Melting of floating ice will freshen ocean but
  cause no MSL rise (Archimedes) gt only steric
  rise
• 3. Freshwater import from continents gt eustatic
  AND steric rise

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Eustatic or steric?
? 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
Source Ocean Freshening, Sea Level Rising,
Walter Munk, Science 27 June 2003 300 2041-2043
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Eustatic or steric?

• 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
• gt 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!
Source Ocean Freshening, Sea Level Rising,
Walter Munk, Science 27 June 2003 300 2041-2043
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predicted future 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
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Updating estimate in IPCC AR4
S. Rahmstorf, Science 315, 368 (2007). M.
Vermeer, S. Rahmstorf, Proc. Natl. Acad. Sci.
U.S.A. 106, 21527 (2009). A. Grinsted, J. C.
Moore, S. Jevrejeva, Clim. Dyn. 34, 461 (2009).
AR4 projections for the A1FI
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Updating estimates in recent works
Source Has the IPCC underestimated the risk of
sea level rise? Stefan Rahmstorf, Nature, 2010
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Interactions between ice sheets, ocean, and
atmosphere affect the balance of mass of the
Greenland and Antarctic ice sheets. The dynamic
response of the ocean may bring warmer waters in
contact with marine glaciers, leading to the
decay of ice shelves. Rapid changes at the
boundary of the ice sheets can be communicated
far into the interior of the ice sheets by ice
streams, leading to unloading of the continent
and changes in the global gravitational field and
thus sea level. Changes in atmospheric
temperatures and circulation may bring more
precipitation to the Antarctic, offsetting ice
loss at the boundaries. (source Regional
Sea-Level Projection, Willis and Church, Science,
2012)
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Summary

• 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
• IPCC likely underestimates the risk of SLR
• Interaction of processes still not well understood