Download Climate Change: possible impacts on coastal systems

Climate Change: possible
impacts on coastal systems
Dennis S. Gonguez
Meteorologist
National Meteorological Service
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.
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
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.
Present State of the Climate (Sea Level
Rise)
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.
Projected state of the climate (temperature
change and sea level rise)
 For
the next two decades a warming of
about 0.2°C 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 0.1°C per decade would be
expected.
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.
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)
Projected state of the climate (temperature
change and sea level rise)
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
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.
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.
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
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)
Vulnerability of coastal systems (reefs)
 Stronger
hurricanes cause more coral
loss but the second of two hurricanes
cause little additional damagegreater future effect on increasing
intensity than increasing frequency.
 There is limited evidence that global
warming may result in an increase in
coral range.
Vulnerability of coastal systems (reefs)
 Warmer
temperatures: Bleaching
usually occurs when the temperature
exceeds a threshold of 0.8 to 1°C
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)
Vulnerability of coastal systems (reefs)
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)
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.
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)
Impacts on coastal ecosystems
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.
 Many coastal regions are already
feeling the effects of local sea level rise
from a combination of climate-induced
changes, geologic and anthropogenicinduced 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
END
• Thanks for you attention
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): 174184
• Hoegh-Guldberg O. 1999, Climate Change, coral bleaching
and the future of the world’s coral reef. Marine and
Freshwater Research 50 (8) 839-866.
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.
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.