Climate Change: possible impacts on coastal systems

1. Climate Change: possible impacts on coastal systems Dennis S. Gonguez Meteorologist National Meteorological Service

2. 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.

3. 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

4. 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.

5. Present State of the Climate (Sea Level Rise)

6. 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.

7. 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.

8. 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.

9. 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)

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

11. 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

12. 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.

13. 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.

14. 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

15. 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)

16. 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.

17. 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)

18. Vulnerability of coastal systems (reefs)

19. 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)

20. 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.

21. 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)

22. Impacts on coastal ecosystems

23. 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.

24. 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

25. END • Thanks for you attention

26. 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 world’s coral reef. Marine and Freshwater Research 50 (8) 839-866.

27. References • Hoegh-Guldberg O. Coralreefs in a centuryof 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.

28. 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.