IPCC Report.pdf - Adam Curry

Changes in Climate Extremes and their Impacts on the Natural Physical EnvironmentChapter 3and using a simple inundation model with high-resolution Light Detectionand Ranging (LIDAR) data and a land subdivision database, identifiedthe impact of inundation on several coastal towns along the southeasternAustralian coastline under future sea level and wind speed scenarios.Probabilistic approaches have also been used to evaluate extreme sealevel exceedance under uncertain future sea level rise scenarios. Purviset al. (2008) constructed a probability distribution around the range offuture sea level rise estimates and used Monte Carlo sampling to applythe sea level change to a two-dimensional coastal inundation model.They showed that by evaluating the possible flood-related losses inthis framework they were able to represent spatially the higher lossesassociated with the low-frequency but high-impact inundation eventsinstead of considering only a single midrange scenario. Hunter (2010)combined sea level extremes evaluated from observations with projectionsof sea level rise to 2100 and showed, for example, that planning levelsin Sydney, Australia, would need to be increased substantially to copewith increased risk of flooding. Along the Portuguese coast, Andrade etal. (2007) found that projected future climate in the HadCM3 modelwould not affect wave height along this coastline but the projectedrotation in wave direction would increase the net littoral drift and theerosional response. Along a section of the southeast coast of the UnitedKingdom, the effect of sea level rise, surge, and wave climate change onthe inshore wave climate was evaluated and the frequency and heightof extreme waves was projected to increase in the north of the domain(Chini et al., 2010). On the basis of modeling the 25-year beach responsealong a stretch of the Portuguese coast to various climate changescenarios, Coelho et al. (2009) concluded that the projected stormierwave climate led to higher rates of beach erosion than mean sea levelrise. Modeling of the evolution of soft rock shores with rising sea levelshas revealed a relatively simple relationship between sea level rise andthe equilibrium cliff profile (Walkden and Dickson, 2008).To summarize, recent observational studies that identify trendsand impacts at the coast are limited in regional coverage, whichmeans there is low confidence, due to insufficient evidence,that anthropogenic climate change has been a major cause ofany observed changes. However, recent coastal assessments atthe national and regional scale and process-based studies haveprovided further evidence of the vulnerability of low-lyingcoastlines to rising sea levels and erosion, so that in the absenceof adaptation there is high confidence that locations currentlyexperiencing adverse impacts such as coastal erosion andinundation will continue to do so in the future due to increasingsea levels in the absence of changes in other contributing factors.3.5.6. Glacier, Geomorphological, and Geological ImpactsMountains are prone to mass movements including landslides, avalanches,debris flows, and flooding that can lead to disasters. Changes in thecryosphere affect such extremes, but also water supply and hydropowergeneration. Many of the world’s high mountain ranges are situated atthe margins of tectonic plates, increasing the possibility of potentiallyhazardous interactions between climatic and geological processes. Theprincipal drivers are glacier ice mass loss, mountain permafrostdegradation, and possible increases in the intensity of precipitation(Liggins et al., 2010; McGuire, 2010). The possible consequences arechanges in mass movement on short contemporary time scales, andmodulations of seismicity and volcanic activity on longer, century tomillennium time scales.The AR4 assessed that “the late 20th century glacier wastage likely hasbeen a response to post-1970 warming” (Lemke et al., 2007). However,the impacts of glacier retreat on the natural physical system in thecontext of changes in extreme events were not assessed in detail.Additionally, the AR4 did not assess geomorphological and geologicalimpacts that might result from anthropogenic climate change. The moststudied change in the high-mountain environment has been the retreatof glaciers (Paul et al., 2004; Kaser et al., 2006; Larsen et al., 2007;Rosenzweig et al., 2007). Alpine glaciers around the world were atmaximum extent by the end of the Little Ice Age (~1850), and haveretreated since then (Leclercq et al., 2011), with an accelerated decayduring the past several decades (Zemp et al., 2007). Most glaciers haveretreated since the mid-19th century (Francou et al., 2000; Cullen et al.,2006; Thompson et al., 2006; Larsen et al., 2007; Schiefer et al., 2007; Pauland Haeberli, 2008). Rates of retreat that exceed historical experience andinternal (natural) variability have become apparent since the beginning ofthe 21st century (Reichert et al., 2002; Haeberli and Hohmann, 2008).Outburst floods from lakes dammed by glaciers or unstable moraines [or‘glacial lake outburst floods’ (GLOFs)] are commonly a result of glacierretreat and formation of lakes behind unstable natural dams (Clarke,1982; Clague and Evans, 2000; Huggel et al., 2004; Dussaillant et al.,2010). In the past century, GLOFs have caused disasters in many highmountainregions of the world (Rosenzweig et al., 2007), including theAndes (Reynolds et al., 1998; Carey, 2005; Hegglin and Huggel, 2008),the Caucasus and Central Asia (Narama et al., 2006; Aizen et al., 2007),the Himalayas (Vuichard and Zimmermann, 1987; Richardson andReynolds, 2000; Xin et al., 2008; Bajracharya and Mool, 2009; Osti andEgashira, 2009), North America (Clague and Evans, 2000; Kershaw et al.,2005), and the European Alps (Haeberli, 1983; Haeberli et al., 2001;Vincent et al., 2010). However, because GLOFs are relatively rare, it isunclear whether their frequency of occurrence is changing at either theregional or global scale. Clague and Evans (2000) argue that outburstfloods from moraine-dammed lakes in North America may have peakeddue to a reduction in the number of the lakes since the end of the LittleIce Age. In contrast, a small but not statistically significant increase ofGLOF events was observed in the Himalayas over the period 1940 to2000 (Richardson and Reynolds, 2000), but the event documentationmay not be complete. Over the past several decades, human mitigationmeasures at unstable glacier lakes in the Himalaya and European Alpsmay have prevented some potential GLOF events (Reynolds, 1998;Haeberli et al., 2001).Evidence of degradation of mountain permafrost and attendant slopeinstability has emerged from recent studies in the European Alps186