Roger Revelle Lecture

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Roger Revelle
Gulf of California Expedition, 1939. (Left to
Right) Erik Moberg, Roger Revelle, Seaman Andrew
Boffinger, Richard Fleming (with binoculars),
Machinist Bob MacDonald, George Hale, Lee Haines,
Engineer Walter Robinson, Martin Johnson, and
Loye H. Miller. SIO Archives, UCSD.
Roger in 1976. Photo by Glasheen. Negative
AN24y 41906y484y34, UCSD Special Collections.
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Revelle on the Oceans and Climate

• The oceans exert a profound influence on mankind
  and indeed upon all forms of life on Earth. The
  oceans are inexhaustible sources of water and
  heat, and control the climate of many parts of
  the world.
• Roger Revelle, 1960
• We cannot forecast it (climate) now we may never
  be able to forecast it, but if we could, the
  results would be so valuable that the gamble is
  worth taking the possible role of the IOC in
  that programme represents the greatest challenge
  and the greatest responsibility that this body in
  my experience has ever had.
• Roger Revelle 1969

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Early comments from Roger Revelle on Climate
Change

• human beings are now carrying out a large scale
  geophysical experiment of a kind that could have
  not have happened in the past nor be reproduced
  in the future
• Roger Revelle 1957
• the grandfather of the greenhouse effect

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Revelle on the Oceans and Climate

• His 1979 address on climate to the Eleventh IOC
  Assembly was a typical Revelle tour de force. As
  one of the first scientists to point to the role
  of the ocean in the climate system and in climate
  variability, he began I am about to describe
  what I believe to be the most important programme
  that has challenged the IOC in many years.
• Extract courtesy of Roger Revelle and his
  contribution to International Ocean Science by
  the honourable John A. Knauss, Revelle Memorial
  Lecture, 1992

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Global sea levels Past, present and future
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Focus on recent progress in our understanding of
sea-level change

• Draw on
• My own work and publications
• The literature
• Results from the WCRP Sea-level Workshop hosted
  by IOC (163 participants, 29 nations)

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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes
• Present rates of change
• Why does sea level change?
• Extreme events
• Future sea-level rise
• Reducing uncertainty
• Key Messages

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Key Impacts in the coastal zone

• Sea-level rise
• inundation
• storm surges, waves
• coastal erosion
• Impacts on emergency and escape routes
• Break down in law and order
• Environmental refugees a here and now issue
• not if but when and where and how will we
  respond?

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Wide range of projections
People to respond
Can measure sea-level rise in other units!

• Tens to
• hundreds of
• millions
• (far fewer
• with
• optimum
• protection)

Nicholls, in prep
Church et al., 2001
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Stabilisation costs
Tens to hundreds of billions of dollars
Nicholls, in prep
Church et al., 2001
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Wetland Loss

• 25-45
• With impacts on biodiversity

Church et al., 2001
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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes

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Sea level has fluctuated by more than 120 m over
the last glacial cycle
Church et al., 2001
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Paleo data constrains estimates of sea-level
change over centuries to millenia, thus estimates
of ice sheet contributions
Lambeck, Pers. Comm., 2006
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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes
• Present rates of change

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Global Mean Sea Level
Seasonal variations removed GIA correction
applied (0.3 mm/year)
Rate 3.2 0.4 mm/year
http//sealevel.colorado.edu
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The distribution of available sea-level data
changes with time
Church and White, 2006
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Estimate sea-level by representing the
interannual variability using patterns determined
from altimeter data
Church and White, 2006
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Sea level estimates for 1870 to 2000 indicate an
acceleration in the rate of rise,a 20th century
rise of about 1.7 mm yr-1
Church and White, 2006
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The rate of rise for the satellite period (1993
on) is greater than the 20th century average (but
similar to earlier periods)
Rate of sea-level rise
Church and White, 2006
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Rise not uniform - climate variability. Pattern
mostly explained by thermal expansion
Domingues et al., in preparation
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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes
• Present rates of change
• Why does sea level change?

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Estimates of upper ocean thermosteric sea level
rise, 1993 - 2003
Domingues et al., 2006
Willis et al., 2004, Lyman et al. 2006
Estimates of thermosteric sea level rise from
1993 2003 using a variety of analysis
techniques (Willis et al., 2004, Lombard et al.,
2005, Domingues et al., 2006) are similar, about
1.6 mm/yr (about 1.3 mm/yr for OI estimates), but
with interannual differences. All of these are
strongly dependent on XBT data. Does the 1998
ENSO signal seen in sea level have a thermosteric
component?
Lombard et al., 2005
Roemmich et al., in preparation
Need to reconcile these differences.
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Ocean thermal expansion significant contribution
Domingues et al., in preparation
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Title slide
Explosive volcanic eruptions contribute to
variability in global sea levels
Mt Pinatubo eruption in the Philippines, June 15,
1991. Gases and solids injected 20 km into the
stratosphere.
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Volcanoes result in a rapid fall in sea level of
5 mm and a masking of the acceleration in
sea-level rise
Church et al., 2005
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Glacier melting contributes to sea level
0.8 /- 0.4 mm/yr
From Position Paper Cryospheric
Contributions (Steffen et al., inpreparation)
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Contribution of Ice sheets to Sea Level
1. Greenland
Zwally et al. (2005) Krabill et al. (2004) Thomas
et al. (2006) Vellicogna and Wahr
(2005) Ramillien et al. (2006) Rignot
Kanagaratnam (2006)
0.3 /- 0.15 mm/yr
2. Antarctica probable net loss but close to
balance
A major advance in our knowledge of ice-sheet
contributions
From Position Paper Cryospheric Contributions
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Effect of global land water storage on global
mean sea level

• greatest variation is associated with ground
  water, followed by soil moisture
• no significant trend was detected
• strong decadal variability driven by
  precipitation, strong decrease in the beginning
  of 1970s

Milly, P. C., D., A. Cazenave, and M. C. Gennero
(Proc. Natl Acad. Sci, 2003) Ngo-duc T., K.
Laval, J. Polcher, A. Lombard and A. Cazenave
(GRL, 2005)
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What do people do to affect sea-level rise?

• Ground Water Mining
• Deforestation
• Desertification
• Wetland filling or drainage
• Surface Water Diversion
• Dam Building
• The sum of these terms poorly known

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Impacts exacerbated by subsiding Coastal
Megacities (during the 20th Century)
Tianjin (2 m)
Dhaka
Seoul
Osaka (3 m)
Istanbul
Tokyo (5 m)
New York
Shanghai (3 m)
Los Angeles
Manila
Lagos
Bangkok (2 m)
Bombay
Nicholls, in prep.
Lima
Karachi
Madras
Jakarta
Rio de Janeiro
Buenos Aires
Calcutta
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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes
• Present rates of change
• Why does sea level change?
• Extreme events

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Bay of Bengal Major Surges 1737 300,000
killed 1864 100,000 1876 100,000 1897 175,000 1970
300,000 (tide plus 6m surge) And at least 23
surge events with over 10,000 killed since
1737 These considered lower limits as economic
damage adds to eventual total (Murty, Flather
and Henry, 1986 Progress In Oceanography Murty
and Flather, 1994 Journal of Coastal Research)
Woodworth et al., in prep.
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The frequency of flooding events of a given
magnitude has increased
A 1 in 5 year event becomes a 1 in 2 year event.

Church et al., submitted
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Locations where the period between flooding
events has decreased are shown in red. Top
relative sea level Bottom relative to yearly
average sea level
99 Percentile Trends since 1975 (Woodworth and
Blackman, 2004 J. Climate)
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The integrated intensity of tropical cyclones has
increased
Emanuel, 2005
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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes
• Present rates of change
• Why does sea level change?
• Extreme events
• Future sea-level rise

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Sea-level rise is projected to continue
Church et al., 2001
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Projections using historical data consistent with
(lower bound for?) model projections
Church and White, 2006
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Stabilisation of concentrations does not mean
immediate stabilisation of temperature and sea
level
Stabilisation of emissions will result in larger
rates of change
Meehl et al., 2005
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• Increasing concern about ice-sheet stability and
  a substantially larger rise in sea level
• Surface melting
• For sustained warmings above 4.50.9 K in
  Greenland (3.10.8 K in global average), it is
  likely that the ice sheet would eventually be
  eliminated. Gregory and Huybrechts, accepted
• Dynamic instability

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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes
• Present rates of change
• Why does sea level change?
• Extreme events
• Future sea-level rise
• Reducing uncertainty

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Reducing uncertainty Observational Principles

• An open data policy with timely, unrestricted
  access for all.
• Data archaeology
• Satellite observations need to be as continuous
  as possible, with overlap between successive
  missions and coincident with the collection of
  appropriate in situ observations.

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Reducing uncertaintySustained, Systematic
Observing Systems

• Sea level.
• Extend the Jason series of satellite altimeters
  through implementation of a Jason-3.
• Complete the GLOSS network of tide gauges,
  absolute positioning, real-time data
• Ocean volume.
• Complete and sustain the Argo array of profiling
  floats.
• Mass.
• Sustain observations of the time-varying gravity
  field, GRACE and follow-on missions
• Terrestrial water storage, Ice sheet mass
  balance, Changes in oceanic mass.

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Reducing uncertainty Sustained, Systematic
Observing Systems

• Ice sheet and glacier topography and thickness.
• Sustain radar altimeters (e.g., ENVISAT), ICESat
  and, once launched, CryoSat-2 altimetric
  satellites complemented by aircraft and in situ
  observations
• Reference frame.
• Strengthen and sustain support for the
  International Terrestrial Reference Frame
• SLR, VLBI DORIS
• GNSS (GPS, together with GLONASS Galileo once
  launched)

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Reducing uncertainty Observing Systems

• Ocean volume.
• Extend the Argo-type capability to under the sea
  ice.
• Design and implement an effort to obtain
  observations for the deep ocean
• Ice sheet and glacier topography.
• Based on experience gained with radar and laser
  satellite altimeters, develop a suitable
  follow-on satellite.
• Ice velocity.
• Interferometric Synthetic Aperture Radar (InSAR)
  mission to observe flow rates in glaciers and ice
  sheets.
• Surface topography.
• Develop and implement the proposed WaTer mission
  with a wide-swath altimeter and interferometric
  SAR to observe the
• Two-dimensional surface water levels on land.
• Surface topography of glaciers and ice sheets.
• Sea level associated with the oceanic mesoscale
  field.

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Reducing uncertainty

• Support research programmes to exploit these data
  sets and deliver value to society
• Detailed recommendations from the WCRP Sea-level
  workshop are being finalised.

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Global sea levels Past, present and future

• Outline
• Rationale
• Historical changes
• Present rates of change
• Why does sea level change?
• Extreme events
• Future sea-level rise
• Reducing uncertainty
• Key Messages

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Projected Coastal Megacities 2010 By 2100, tens
of millions/year will have to respond to coastal
flooding Most vulnerable regions are South and
South-East Asia Africa Carribean Indian Ocean
Islands Pacific Ocean Islands.
Tianjin
Dhaka
Seoul
Osaka
Istanbul
Tokyo
New York
Shanghai
Los Angeles
Manila
Bangkok
Lagos
Nicholls, Pers Comm.
Mumbai
Lima
Karachi
Madras
Jakarta
Rio de Janeiro
Buenos Aires
Calcutta
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Key messages

• Sea-level rise is an issue for
• Here and now, The 21st C and The long term
• Need to mitigate to avoid the most extreme
  scenarios
• Need to adapt
• Impacts will be felt through extreme events
  more frequent and more severe
• Need to narrow uncertanties
• Will we pass a major tipping point during the
  21st C
• LDCs and the poor most at risk
• Require local and regional planning
• Planning to avoid disasters
• Environmental refugees a here and now issue
• Not if but when and where and how will we
  respond
• Science/government/business/community partnership
  essential future here and now

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Finally

• What would Roger Revelle think today about our
  grand experiment with planet earth?

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Thank you!