Global Sea Level Change

1
Global Sea Level Change Professor Gordon
Walkden School of Geosciences University of
Aberdeen
West Bay, Bridport, Dorset
2
Silver penny of Cnut (Canute) Danish King of
England (1013-1036)
English King Canute had to demonstrate to his
knights that he lacked power over short term
changes in sea level!
Cnut proves that he is powerless to stem the tide
3
But its not just the tides - Sea level itself
isnt static.
Average sea level records decadal to millennial
changes
Typical tidal records daily and monthly changes
4
And on the longer term?
Tens of thousands of years
Tens to hundreds of millions of years
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Are we as powerless as King Cnut?

• How do we know sea level is changing?

• What causes this change?

• What are the effects of sea level change?

• Can we stop sea level change?

Bridport Harbour, West Bay, Dorset
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First

• How do we know sea level is changing?

• What causes this change?

• What are the effects of sea level change?

• Can we stop sea level change?

7
How do we know sea level is changing?
Aberdeen Harbour Tidal records
Average rise of 0.66mm/a
Harbour records
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How do we know sea level is changing?
Rate of rise 1993-2005 3mm/year
Satellite altimetry
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How do we know sea level is changing?
Change rates vary across the globe oceanic
currents are mostly to blame
Rate of rise 1993-2005 3mm/year
El Nino (every 3-7 years)
Satellite altimetry
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How do we know sea level is changing?
Living foraminifera absorb and preserve the
ambient 16O /18O ratio in the oceans
Fractional enrichment of 18O in the oceans by
removal and storage of 16O in ice
A full record of the changing 16O /18O ratio is
preserved in ocean sediments
Oxygen isotope proxy in seafloor sediment
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How do we know sea level is changing?
Isotope data are converted to equivalent sea
level values
Isotope data for the last 2 ma (chart reversed) -
cyclic swings in sea level

Oxygen isotope proxy in seafloor sediments
12
How do we know sea level is changing?
The Vostok ice core, Antarctica
The CO2 curve from ice is an exact match to the
16O/18O curve from the oceans
The CO2 and other proxies from ice cores
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How do we know sea level is changing?
Belize blue hole a submerged karst cenote
Florida reef once a sea cliff
Submerged stalactites
Geological evidence from karst features
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How do we know sea level is changing?
12,000 years ago
Iraq
Iran
Kuwait
Saudi Arabia
The competing sedimentary systems desert sand,
marine limestone, freshwater mud.
Qatar
UAE
Geological evidence from sediments
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How do we know sea level is changing?
Arabian Gulf Seafloor Cores
Fossil bivalve from core with marine cement
Fossil bivalve from core altered by exposure
Geological evidence from sediments
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How do we know sea level is changing?
Modern Florida karst pits develop beneath trees
Karstic pits, Carboniferous Barns Ness, Dunbar
Fossil root systems Barns Ness
Geological evidence from karst features
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How do we know sea level is changing?
Lower Jurassic marine limestones Oman
There are many fossil karst surfaces in this
succession. They prove alternating marine
deposition and subaerial dissolution
A fossil karst surface
A fossil soil with dissolved shell
Geological evidence from sediments
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Triassic case study
How do we know sea level is changing?
Modern lizard
Unconformity
Triassic alluvium overlies a Carboniferous land
surface SW England
Triassic reptile bones
Fossil Cave
Roof collapse
sediment fill
Geological evidence from sediments
Groundwater ups and downs
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Next

• How do we know sea level is changing?

• What causes sea level change?

• What are the effects of sea level change?

• Can we stop sea level change?

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What causes sea level change?
We must distinguish between two distinct
processes

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What causes sea level change?
1) Tectonically driven processes Agent
Local or regional rises and falls in the
Earths crust Cause The planets internal heat
budget Effect Local, regional and worldwide
sea level change Terms Isostacy Tectonism

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What causes sea level change?
2) Climate - driven processes Agents
Temperature, water runoff, ice
storage Cause Variations in the atmospheric
heat budget and solar input Effect Worldwide
rises and falls in sea level (Global sea level
change) Terms Climatic forcing Eustasy

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Lithospheric Plate movement Large scale,
regional, can have big effect on global sea level
1) Tectonically driven processes
The Zagros front where European plate meets
African plate
Drowned Valley - Dart
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Ocean ridges
1) Tectonically driven processes
Late Cretaceous Global sea level was c.150 200m
higher than today. These famous white cliffs
are only 70-80m high!
The European Chalk was deposited during the late
Cretaceous sea level high
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Ocean ridges
1) Tectonically driven processes
Late Cretaceous Global sea level was c.150 200m
higher than today. These famous white cliffs
are only 70-80m high!
The late Cretaceous sea level high accompanied a
phase of rapid sea floor spreading with hotter,
more buoyant mid ocean ridges
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Isostatic Change Crustal readjustment local to
regional scale minimal effect on global sea
level.
1) Tectonically driven processes
Raised beaches - Jura
UK, mm/a last 5ka
Drowned Valley - Dart
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2) Climate - driven processes
2 Main Processes cause Eustatic (i.e. Global) SLC
1
2
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2) Climate - driven processes Orbital forcing
Orbital forcing of solar energy affects world
climate.
1000 800 600
400 200 NOW

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2) Climate - driven processes Orbital forcing
A Chalk Quarry in Wiltshire Orbital forcing
rhythms are preserved in the pattern of strata
mainly the 41K Obliquity variation
Relative dominance of cycles varies with time
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2) Climate - driven processes Orbital forcing
This rhythmic succession in Oman shows repeated
karsts. Its the same age, and shows that sea
level followed the 41k rhythm
Jurassic cliffs at Lyme Regis, Dorset. The
alternations of limestone and mud are the 41k
rhythm.
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2) Climate - driven processes Orbital forcing
The 100k cycle and Pleistocene Glaciations
Dramatic sea level rise in the last 18,000 years
Header
Rise of 120m
Body text
Average rate of rise 6.6mm/year
in 18k years
Max. rate of rise 0.5 metres/year
www.abdn.ac.uk/
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Sea level rise has been much slower in the last
7000 years
Header

Just 4m in 7000 years Thats 0.57mm/year
Body text
But it is currently getting faster
0.57mm/ year
www.abdn.ac.uk/
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The current trend is upwards
The current figure is 200mm in 100 years.
Thats 2mm/year
Header

Body text
And the Satellite data (red) show the faster rate
of 3mm/year
0.06mm/ year
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2) Climate - driven processes Part of the trend
is thermal expansion as the oceans warm up
Oceans are also warmer at the surface. At depth
they are full of cold sea water from the poles.
The oceans are warmer at the equator
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2) Climate - driven processes Part of the trend
is Thermal expansion of the oceans
Sea level could rise c.20cm for every 10C
increase in sea temperature
Thermal expansion of the oceans could be at the
rate of 1.5mm/ year
NASA estimate that about half the satellite -
detected sea level rise since 1993 is caused by
thermal expansion of the oceans
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Next

• How do we know sea level is changing?

• What causes sea level change?

• What are the effects of sea level change?

• Can we stop sea level change?

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What are the effects of sea level rise?
Loss of habitat and species?

Arctic habitats
Wetlands
Many of these habitats have changed dramatically
in the past and species have survived.
Coral Reefs
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What are the effects of sea level rise?
Changing landscape?
Loss of beach defences

Loss of shingle protection to cliff lines
Loss of property
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What are the effects of sea level rise?
Loss of habitat and environmental resources
hasnt mattered in the last 8,000 years

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What are the effects of sea level rise?

From now on rising sea levels will begin to
matter a great deal more
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What are the effects of sea level rise?
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What are the effects?
Todays population is 6.7 billion
World population is currently rising at the rate
of 1 billion every 10 years
Exponential increase since 1500
Header
Body text
Population has rocketed largely in coastal
cities
Sea level rise has stabilised in the last 7,000
years
www.abdn.ac.uk/
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What are the effects of sea level rise?
Netherlands case study

Solution Build sea defences
Problem Loss of agricultural land
Loss of agricultural and and
Problem Sinking anyway
Further Problem Very expensive
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What are the effects of sea level rise?
New Orleans case study

Hurricane Katrina 2005
Problem Loss of residential and commercial land
Solution Build levees and maintain them
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What are the effects of sea level rise?

More than 60 of world cities are vulnerable to
rising sea levels More than 600 million people
live within 10m of sea level
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What are the effects of sea level rise?

Carteret Atoll, Papua new Guinea population
being moved
Many other low lying oceanic islands face the
same crisis
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What are the political and human consequences?
Unconstrained states
Header
Body text
Armed factions
Environmental migrants?
www.abdn.ac.uk/
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Next

• How do we know sea level is changing?

• What causes sea level change?

• What are the effects of sea level change?

• Can we stop sea level change?

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Can we stop sea level change?
Are CO2 emissions ultimately responsible?
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Will fixing CO2 fix Sea level change?

Changes in temperature and sea level since 1880
correspond
And both these curves follow the same trend as
rising greenhouse emissions
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Can we stop sea level change?
Will fixing CO2 fix Sea level change?
CO2 and sea level are well linked in the past
but does CO2 control sea level?
Or do temperature and sea level control CO2
release?
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Will fixing CO2 fix Sea level change?
Phanerozoic Carbon Dioxide
Sea level and CO2 are also linked in the past.
But what is cause and what is effect?
Carbon Dioxide ppm
500m 400m 300m 200m
100m 0
Global sea level fluctuations
Exxon sea level Changes (m)
We know that large scale sea level change is
plate movement led so CO2 seems to be secondary.
Graphs are reversed to keep Recent on right
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What are the predictions?
High estimate
Low estimate
CO2 may not have led sea level change in the
past, but could it lead SLC in the future?
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Is there another game going on?
Is the temperature trend in the last century
linked to direct solar energy variation?
But the latest trends show a drop in solar input
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Is there a bigger threat around the corner?
The post-industrial rise in greenhouse gas
emissions exceeds all variation recorded by
Pleistocene and Holocene proxies.

Maybe industrially induced global warming is
all that keeps us from the next disastrous ice
age!
Interglacials are short lived.
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Can we stop sea level change?
The post industrial rise in CO2 remains a
potential threat, but can we realistically
control this? Does the third world not also have
the right to industrialisation?
Are you willing to close down all blacksmiths and
potters, and to stop felling trees?
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The 21st Century Agenda
Global environmental change
Environmental refugees
Population explosion
Global sea level change
Cultures in conflict
Global pandemics
Crime/ corruption
Climatic extremes
Poverty and food
Global pollution
World health
Sustainability
State terrorism
Biotechnology
Finite resources
Natural disasters
Exploiting the oceans
Global water supply
Recycling technologies
Global energy supply
Exploiting the solar system
Alternative energy sources
Are we ready?
Managing mixed societies
Global biodiversity loss
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Are we ready?
Global Challenges
The new multidisciplinary B.Sc. degree programme
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Conclusions

• Sea level change is a response to many natural
  controlling variables.

• Sea level oscillates on a range of timescales and
  magnitudes

• The biggest short term influence on global sea
  level is temperature

• Glacioeustacy and thermal expansion are the main
  processes

• CO2 has not been the driver of sea level change
  at least until now

• There is clear evidence for a big post-industrial
  increase in CO2

• Future scenarios of sea level change are based on
  CO2 and other greenhouse gasses as drivers of
  temperature increase

• Most modern species have already survived rapid
  rise in sea level so will not become extinct as a
  result of relatively minor changes

• Sea level change involving metres, would have
  substantial effects on world populations in
  coastal areas, including many great cities.

• The biggest threat faced by humanity as a whole
  is not a future rise in sea level but the
  certainty of the next ice age and a big chill

• We can build defences that keep the sea out

• We have no ethical defences against displaced
  people

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References
Images All of the geological images come from
personal research and field study folders The
remaining locational shots come from images
sourced using a wide range of search phrases in
Google Images. Graphs Nearly all the best graphs
come from a single source Global Warming Art
(http//www.globalwarmingart.com/wiki/Thumbnail_ga
llery_of_all_images). This includes non-biased
explanatory text and is an excellent resource.
Other graphs come from NASA, e.g.(earthobservatory
.nasa.gov/Library/GlobalWarmingte/ ) Text
information Useful and reliable material is
found on the above websites and also on
Wikipedia. E.g. (http//en.wikipedia.org/wiki/Sea
_level_rise) Several universities have accessible
online course notes and illustrations. Always
beware of non peer reviewed personal, blog and
single interest group websites IPCC
Reports Reports by the Inter Governmental Panel
on Climate Change are available at
http//www.ipcc.ch/. Look for the 23 page
Summary for Policymakers (November 2007) which
summarises the three main reports and the
synthesis report published at that time.