IPCC Report.pdf - Adam Curry

Chapter 3Changes in Climate Extremes and their Impacts on the Natural Physical EnvironmentCoral reefs are a feature of many small islands and healthy reef systems mitigate against erosion and inundation by not only providing abuffer zone for the shoreline during extreme surge and wave events but also providing a source of carbonate sand and gravel, which aredelivered to the shores by storms and swell to maintain the atoll (Woodroffe, 2008; Webb and Kench, 2010). Anthropogenic oceanicchanges may indirectly contribute to extreme impacts for coral atolls by affecting the health of the surrounding reef system. Suchchanges include: (1) warming of the surface ocean, which slows or prevents growth in temperature-sensitive species and causes morefrequent coral bleaching events (e.g., Hoegh-Guldberg, 1999; see also Chapter 4); (2) ocean acidification, caused by increases inatmospheric CO 2 being absorbed into the oceans, which lowers coral growth rates (Bongaerts et al., 2010); and (3) reduction in oxygenconcentration in the ocean due to a combination of changes in temperature-driven gas solubility (Whitney et al., 2007), ocean ventilationdue to circulation changes, and biological cycling of organic material (Keeling et al., 2010). Quantifying these changes and understandingtheir impact on coral reef health will be important to understanding the impact of anthropogenic climate change on atolls.In summary, the small land area and often low elevation of small island states make them particularly vulnerable to risingsea levels and impacts such as inundation, shoreline change, and saltwater intrusion into underground aquifers. Shortrecord lengths and the inadequate resolution of current climate models to represent small island states limit the assessmentof changes in extremes. There is insufficient evidence to assess observed trends and future projections in rainfall across thesmall island regions considered here. The reported increases in warm days and nights and decreases in cold days andnights are of medium confidence over the Caribbean and of low confidence over the Pacific and Indian Oceans. There ismedium confidence in the projected temperature increases across the Caribbean. The unique situation of small islandsstates and their maritime environments leads to an additional emphasis on oceanic information to understand the impactsof climate change. The very likely contribution of mean sea level rise to increased coastal high water levels, coupled withthe likely increase in tropical cyclone maximum wind speed, is a specific issue for tropical small island states.exacerbated by increasing human-induced pressures (Nicholls et al.,2007). However it was also noted that since coasts are dynamic systems,adaptation to climate change required understanding of processesoperating on decadal to century time scales, yet this understanding wasleast developed.Because of the diverse and complex nature of coastal impacts, assessmentsof the future impacts of climate change have focused on a wide rangeof questions and employed a diverse range of methods, making directcomparison of studies difficult (R.J. Nicholls, 2010). Two types of studiesare examined here: the first are assessments, typically undertaken at thecountry or regional scale and which combine information on physicalchanges with the socioeconomic implications (e.g., Nicholls and de laVega-Leinert, 2008); the second type are studies oriented around improvedscientific understanding of the impacts of climate change. In terms ofcoastal assessments, Aunan and Romstad (2008) reported that Norway’sgenerally steep and resistant coastlines contribute to a low physicalsusceptibility to accelerated sea level rise. Nicholls and de la Vega-Leinert(2008) reported that large parts of the coasts in Great Britain (includingEngland, Wales, and Scotland) are already experiencing widespreadsediment starvation and erosion, loss/degradation of coastal ecosystems,and significant exposure to coastal flooding. Lagoons, river deltas, andestuaries are assessed as being particularly vulnerable in Poland (Pruszakand Zawadzka, 2008). In Estonia, Kont et al. (2008) reported increasedbeach erosion, which is believed to be the result of increased storminessin the eastern Baltic Sea since 1954, combined with a decline in sea icecover during the winter. Sterr (2008) reported that for Germany there isa high level of reliance on hard coastal protection against extreme sealevel hazards, which will increase ecological vulnerability over time. InFrance, the Atlantic coast Aquitaine region was considered moreresilient to rising sea levels over the coming century because of thesediment storage in the extensive dune systems whereas the sandycoast regions of the Languedoc Roussillon region on the Mediterraneancoast were considered more vulnerable because of narrow dunesystems that are also highly urbanized (Vinchon et al., 2009). A coastalvulnerability assessment for Australia (Department of Climate Change,2009) characterized future vulnerability in terms of coastal geomorphology,sediment type, and tide and wave characteristics, from which it concludedthat the tropical northern coastline would be most sensitive to changesin tropical cyclone behavior while health of the coral reefs may alsoinfluence the tropical eastern coastline. The mid-latitude southern andeastern coastlines were expected to be most sensitive to changes inmean sea level, wave climate, and changes in storminess. A comparativestudy of the impact of sea level rise on coastal inundation across 84developing countries showed that the greatest vulnerability to a 1 msea level rise in terms of inundation of land area was located in EastAsia and the Pacific, followed by South Asia, Latin America, and theCaribbean, the Middle East and North Africa, and finally sub-SaharanAfrica (Dasgupta et al., 2009).New models have been developed for the assessment of coastalvulnerability at the global to national level (Hinkel and Klein, 2009). Atthe local to regional scale, new techniques and approaches have alsobeen developed to better quantify impacts from inundation due tofuture sea level rise. Bernier et al. (2007) evaluated spatial maps ofextreme sea level for different return periods on a seasonal basis thatwere used to estimate seasonal risk of inundation under future sea levelscenarios. McInnes et al. (2009a) developed spatial maps of storm tide185