220.127.116.11 Sea levels
Sea-level changes are of special significance, not only for the low-lying atoll islands but for many high islands where settlements, infrastructure and facilities are concentrated in the coastal zone. Projected globally averaged sea-level rise at the end of the 21st century (2090 to 2099), relative to 1980 to 1999 for the six SRES scenarios, ranges from 0.19 to 0.58 m (Meehl et al., 2007). In all SRES scenarios, the average rate of sea-level rise during the 21st century very probably exceeds the 1961 to 2003 average rate (1.8 ± 0.5 mm/yr). Climate models also indicate a geographical variation of sea-level rise due to non-uniform distribution of temperature and salinity and changes in ocean circulation. Furthermore, regional variations and local differences depend on several factors, including non-climate-related factors such as island tectonic setting and postglacial isostatic adjustment. While Mörner et al. (2004) suggest that the increased risk of flooding during the 21st century for the Maldives has been overstated, Woodworth (2005) concludes that a rise in sea level of approximately 50 cm during the 21st century remains the most reliable scenario to employ in future studies of the Maldives.
18.104.22.168 Extreme events
Global warming from anthropogenic forcing suggests increased convective activity but there is a possible trade-off between localised versus organised convection (IPCC, 2001). While increases in SSTs favour more and stronger tropical cyclones, increased isolated convection stabilises the tropical troposphere and this, in turn, suppresses organised convection, making conditions less favourable for vigorous tropical cyclones to develop. Thus, the IPCC (2001) noted that changes in atmospheric stability and circulation may produce offsetting tendencies.
Recent analyses (e.g., Brazdil et al., 2002; Mason, 2004) since the TAR confirm these findings. Climate modelling with improved resolutions has demonstrated the capability to diagnose the probability of occurrence of short-term extreme events under global warming (Meehl et al., 2007). Vassie et al. (2004) suggest that scientists engaged in climate change impact studies should also consider possible changes in swell direction and incidence and their potential impacts on the coasts of small islands. With an increasing number of people living close to the coast, deep ocean swell generation, and its potential modifications as a consequence of climate change, is clearly an issue that needs attention, alongside the more intensively studied topics of changes in mean sea level and storm surges.
Although there is as yet no convincing evidence in the observed record of changes in tropical cyclone behaviour, a synthesis of the recent model results indicates that, for the future warmer climate, tropical cyclones will show increased peak wind speed and increased mean and peak precipitation intensities. The number of intense cyclones is likely to increase, although the total number may decrease on a global scale (Meehl et al., 2007). It is likely that maximum tropical cyclone wind intensities could increase, by 5 to 10% by around 2050 (Walsh, 2004). Under this scenario, peak precipitation rates are likely to increase by 25% as a result of increases in maximum tropical cyclone wind intensities, which in turn cause higher storm surges. Although it is exceptionally unlikely that there will be significant changes in regions of formation, the rate of formation is very likely to change in some regions. Changes in tropical cyclone tracks are closely associated with ENSO and other local climate conditions. These suggest a strong possibility of higher risks of more persistent and devastating tropical cyclones in a warmer world.
Mid-latitude islands, such as islands in the Gulf of St. Lawrence and off the coast of Newfoundland (St. Pierre et Miquelon), are exposed to impacts from tropical, post-tropical, and extra-tropical storms that can produce storm-surge flooding, large waves, coastal erosion, and (in some winter storms) direct sea ice damage to infrastructure and property. Possible increases in storm intensity, rising sea levels, and changes in ice duration and concentration, are projected to increase the severity of negative impacts progressively, particularly by mid-century (Forbes et al., 2004). In the Queen Charlotte Islands (Haida Gwaii) off the Canadian Pacific coast, winter storm damage is exacerbated by large sea-level anomalies resulting from ENSO variability (Walker and Barrie, 2006).