Climate Change: possible impacts on coastal systems

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Climate Change possible impacts on coastal
systems

• Dennis S. Gonguez
• Meteorologist
• National Meteorological Service

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Format

• Present state of the climate
• Projected state of the climate
• Vulnerability of coastal systems
• Possible impacts of climate change on coastal
  systems and low lying areas.

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Present State of the Climate

• Conclusions of the Intergovernmental Panel on
  Climate Change (IPCC) Working Group I (WG I)
  Physical Science Basis
• Warming of the climate system is unequivocal, as
  is now evident from observations of global
  average air and ocean temperature, widespread
  melting of snow and ice and rising sea levels
• Eleven of the last twelve years (1995-2006) rank
  among the warmest years in the instrumental
  record of global surface temperatures.
• The linear warming trend over the last 50 years
  is nearly twice for the last 100 years

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Present State of the Climate (sea level rise)

• Observations since 1961 show that the average
  temperature of the global ocean has increased to
  depths of at least 3,000 m and that the ocean has
  been absorbing more than 80 of the heat added to
  the climate system. Such warming causes seawater
  to expand, contributing to sea level rise.

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Present State of the Climate (Sea Level Rise)
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Present State of the Climate (sea level rise)

• Global average sea level rose at an average rate
  of 1.8 mm per year over the 1961-2003 period.
  There is a high confidence that the rate of
  observed sea level rise increased from the 19th
  to 20th century. The total 20th century rise is
  estimated to be 0.17 m.
• Sea level rise and human development are both
  contributing to losses of coastal wetlands and
  mangroves and increasing damage from coastal
  flooding in many areas.

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Projected state of the climate (temperature
change and sea level rise)

• For the next two decades a warming of about 0.2C
  per decade is projected for a range of Special
  Reduction Emission Scenarios. Even if the
  concentration of all greenhouse gases and
  aerosols had been kept constant at year 2000
  levels, a further warming of 0.1C per decade
  would be expected.

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Projected state of the climate (temperature
change and sea level rise)

• Increasing atmospheric carbon dioxide
  concentrations lead to increasing acidification
  of the ocean. Projections based on SRES scenarios
  give reductions in average global surface pH of
  between 0.14 and 0.35 units, over the 21st
  century, adding to the present decrease of 0.1
  units since pre-industrial times.

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Projected state of the climate
Projected change in air temperature (C) by
region (Ruosteenoja et al 2003
Projected change in precipitation () by region
(Ruosteenoja et al 2003)
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Projected state of the climate (temperature
change and sea level rise)
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Vulnerability of coastal systems ecosystems

• Coastal ecosystems are likely to respond to
  external forcing in a non-linear manner.
• Initial response to dampen effects of the change
  
• Response is amplified if thresholds in magnitude
  or rate of change is surpassed

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Vulnerability of coastal systems ecosystems

• Transitions between states may be triggered or
  total system collapse
• Species may show rapid transition to a much less
  productive and/or species poor assemblage with
  poorer biomass and other impairments.
• Climate change forcing increases ocean thermal
  stratification and reduces upwelling.

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Vulnerability of coastal systems (reefs)

• Effects of decreasing pH leads to decreasing
  aragonite saturation state, one of the main
  physiochemical determinants of coral
  calcification. (Kleypas et al,1999)
• There are no data currently relating altered
  coral growth in field to increasing acidity.

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Vulnerability of coastal systems (reefs)

• Increased intensity of tropical storms and
  hurricanes storms damage corals directly through
  wave action and indirectly by light attenuation
  by suspended sediments and by abrasion by
  sediment and broken corals.
• Passage of storms affect species composition and
  abundance from which the reef ecosystems require
  time to recover

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Vulnerability of coastal systems (reefs)

• Coral cover on the Caribbean reefs decreased by
  17 on average in the year following a hurricane
  with no evidence of recovery for 8 years post
  impact (Gardner et al 2005)

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Vulnerability of coastal systems (reefs)

• Stronger hurricanes cause more coral loss but the
  second of two hurricanes cause little additional
  damage- greater future effect on increasing
  intensity than increasing frequency.
• There is limited evidence that global warming may
  result in an increase in coral range.

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Vulnerability of coastal systems (reefs)

• Warmer temperatures Bleaching usually occurs
  when the temperature exceeds a threshold of 0.8
  to 1C above mean summer maximum levels for at
  least four weeks. (Hoegh-Guldberg,1999)
• Mortality leads to loss of structural complexity
  and shifts in reef fish species composition.
  (Bellwood et al 2006)

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Vulnerability of coastal systems (reefs)
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Vulnerability of coastal systems (reefs)

• Global climate change model results imply that
  the thermal thresholds of sea surface temperature
  will be exceeded more frequently with the
  consequence that bleaching will recur more often
  than reefs can sustain. (Donner et al 2005,
  Hoegh-Guldberg 1999, 2004)

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Vulnerability of coastal systems (mangroves)

• Mangrove communities are likely to show a blend
  of positive and negative responses to climate
  change.
• Positive response enhanced growth due to higher
  levels of carbon dioxide and warmer temperature.

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Vulnerability of coastal systems (mangroves)

• Negative impacts such as saline intrusion and
  erosion largely depend on site specific factors.
  (Saenger 2002)
• Groundwater plays an important role in the
  elevation of mangrove soils. The influence of
  hydrology should be considered when evaluating
  the effects of disturbances, sea level rise and
  water management decisions on mangrove systems.
  (Whelan et al 2005)

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Impacts on coastal ecosystems
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Impacts on coastal ecosystems

• Coastal wetlands including salt marshes and
  mangroves are projected to be negatively affected
  by sea level rise especially where they are
  constrained on their landward side or starved of
  sediment.

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• Many coastal regions are already feeling the
  effects of local sea level rise from a
  combination of climate-induced changes, geologic
  and anthropogenic-induced land subsidence among
  other local factors.
• Challenge to separate the meteorological,
  oceanographic, geophysical and anthropogenic
  processes affecting the shoreline in order to
  identify and isolate contributions due to global
  warming

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END

• Thanks for you attention

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References

• Bellwood, D.R., A.S. Hoey, J.L. Ackerman, M.
  Depcynsky 2006.Coralbleaching, community phase
  shifts and the resilience of coral reefs. Global
  Change Biology 12 (19) 1587-1594.
• Donner S.D., W.J. Skirving, C.M. Little, M.
  Oppenheimer, O. Hoegh-Guldberg. 2005. Global
  assessment of coral bleaching and required rates
  of adaptation under climate change. Glob. Change
  Biol.11. 2251-2265.
• Gardner, T.A.,I.M. Cote, A. Grant and A.R.
  Watkinson 2005, Hurricanes and Caribbean Coral
  Reefs impacts, recovery patterns and role in
  long term decline. Ecology, 86 (1) 174-184
• Hoegh-Guldberg O. 1999, Climate Change, coral
  bleaching and the future of the worlds coral
  reef. Marine and Freshwater Research 50 (8)
  839-866.

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References

• Hoegh-Guldberg O. Coralreefs in a century of
  rapid environmental change. Symbiosis 37 1-31.
• Kleypasj.A., R.W. Buddemier, D. Archer,
  J.P.Gattusuo, C. Langdon and B.N. Opdyke 1999
  Geochemical consequences of increased atmospheric
  carbon dioxide on coral reefs. Science,
  284(5411) 118-120
• Nicholls, R.J. Coastal flooding and wetland loss
  in the 21st century changes under the SRES
  climate and socio-economic scenarios. Global
  Environmental Change.14. 69-86.

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References

• Saenger P. 2002. Mangrove ecology, silviculture
  and conservation. Kluwer 360 pp
• Whelan K.T. T.J. Smith, D.R. Cahoon J.C. Lynch
  and G.H. Anderson.2005 Groundwater control of
  mangrove surface elevation Shrink and swell
  varies with soil depth. Esthuaries.28. 833-843.