IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Changes in Climate Extremes and their Impacts on the Natural Physical EnvironmentChapter 3Table 3-1 (continued)Observed Changes (since 1950)Attribution of ObservedChangesProjected Changes (up to 2100) withRespect to Late 20th CenturyImpacts onPhysicalEnvironment(Continued)Extreme SeaLevel andCoastal Impacts(Sections 3.5.3,3.5.4, and 3.5.5)Other PhysicalImpacts(Sections 3.5.6,3.5.7, and 3.5.8)Likely increase in extreme coastal high waterworldwide related to increases in mean sea level inthe late 20th century.Low confidence in global trends in large landslides insome regions. Likely increased thawing of permafrostwith likely resultant physical impacts.Likely anthropogenic influence viamean sea level contributions.Likely anthropogenic influence onthawing of permafrost.Low confidence of otheranthropogenic influences becauseof insufficient evidence for trends inother physical impacts in coldregions.Very likely that mean sea level rise will contribute toupward trends in extreme coastal high water levels.High confidence that locations currently experiencingcoastal erosion and inundation will continue to do sodue to increasing sea level, in the absence of changesin other contributing factors.High confidence that changes in heat waves, glacialretreat, and/or permafrost degradation will affect highmountain phenomena such as slope instabilities, massmovements, and glacial lake outburst floods. Highconfidence that changes in heavy precipitation willaffect landslides in some regions.Low confidence in projected future changes in dustactivity.Notes: 1. Due to trends in stratospheric ozone concentrations.and snow affect extremes in specific regions (hot extremes in transitionalclimate regions, and cold extremes in snow-covered regions), where theymay induce significant deviations in changes in extremes versus changesin the average climate, as also discussed in Section 3.1.6. Other relevantfeedbacks involving extreme events are those that can lead to impactson the global climate, such as modification of land carbon uptake dueto enhanced drought occurrence (e.g., Ciais et al., 2005; Friedlingstein etal., 2006; Reichstein et al., 2007) or carbon release due to permafrostdegradation (see Section 3.5.7). These aspects are not, however,specifically considered in this chapter (but see Section 3.1.7, onprojections of possible increased Amazon drought and forest dieback inthis region). Chapter 4 also addresses feedback loops betweendroughts, fire, and climate change (Section 4.2.2.1).3.1.5. Confidence and Likelihoodof Assessed Changes in ExtremesIn this chapter, all assessments regarding past or projected changes inextremes are expressed following the new IPCC Fifth Assessment Reportuncertainty guidance (Mastrandrea et al., 2010). The new uncertaintyguidance makes a clearer distinction between confidence and likelihood(see Box SPM.2). Its use complicates comparisons between assessmentsin this chapter and those in the IPCC Fourth Assessment Report (AR4), asthey are not directly equivalent in terms of nomenclature. The followingprocedure was adopted in this chapter (see in particular the ExecutiveSummary and Tables 3-1, 3-2, and 3-3.):• For each assessment, the confidence level for the given assessmentis first assessed (low, medium, or high), as discussed in the nextparagraph.• For assessments with high confidence, likelihood assessments of adirection of change are also provided (virtually certain for 99-100%,very likely for 90-100%, likely for 66-100%, more likely than notfor 50-100%, about as likely as not for 33-66%, unlikely for 0-33%,very unlikely for 0-10%, and exceptionally unlikely for 0-1%). Ina few cases for which there is high confidence (e.g., based onphysical understanding) but for which there are not sufficientmodel projections to provide a more detailed likelihood assessment(such as ‘likely’), only the confidence assessment is provided.• For assessments with medium confidence, a direction of change isprovided, but without an assessment of likelihood.• For assessments with low confidence, no direction of change isgenerally provided.The confidence assessments are expert-based evaluations that considerthe confidence in the tools and data basis (models, data, proxies) usedto assess or project changes in a specific element, and the associatedlevel of understanding. Examples of cases of low confidence for modelprojections are if models display poor performance in simulating thespecific extreme in the present climate (see also Box 3-2), or if insufficientliterature on model performance is available for the specific extreme, forexample, due to lack of observations. Similarly for observed changes,the assessment may be of low confidence if the available evidence isbased only on scattered data (or publications) that are insufficient toprovide a robust assessment for a large region, or the observations maybe of poor quality, not homogeneous, or only of an indirect nature(proxies). In cases with low confidence regarding past or projectedchanges in some extremes, we indicate whether the low confidence isdue to lack of literature, lack of evidence (data, observations), or lack ofunderstanding. It should be noted that there are some overlapsbetween these categories, as for instance a lack of evidence can be atthe root of a lack of literature and understanding. Cases of changes inextremes for which confidence in the models and data is rated as‘medium’ are those where we have some confidence in the tools andevidence available to us, but there remain substantial doubts aboutsome aspects of the quality of these tools. It should be noted that anassessment of low confidence in observed or projected changes ortrends in a specific extreme neither implies nor excludes the possibilityof changes in this extreme. Rather the assessment indicates lowconfidence in the ability to detect or project any such changes.Changes (observed or projected) in some extremes are easier to assessthan in others either due to the complexity of the underlying processesor to the amount of evidence available for their understanding. This120