IPCC Report.pdf - Adam Curry

Chapter 3Changes in Climate Extremes and their Impacts on the Natural Physical EnvironmentTable 3-1 | Overview of considered extremes and summary of observed and projected changes at a global scale. Regional details on observed and projected changes in temperatureand precipitation extremes are provided in Tables 3-2 and 3-3. Extremes (e.g., cold/warm days/nights, heat waves, heavy precipitation events) are defined with respect to late 20thcenturyclimate (see also Box 3-1 for discussion of reference period).Observed Changes (since 1950)Attribution of ObservedChangesProjected Changes (up to 2100) withRespect to Late 20th CenturyWeatherandClimateVariablesTemperature(Section 3.3.1)Precipitation(Section 3.3.2)Very likely decrease in number of unusually cold daysand nights at the global scale. Very likely increase innumber of unusually warm days and nights at theglobal scale. Medium confidence in increase in lengthor number of warm spells or heat waves in many (butnot all) regions. Low or medium confidence in trends intemperature extremes in some subregions due eitherto lack of observations or varying signal withinsubregions. [Regional details in Table 3-2]Likely statistically significant increases in the numberof heavy precipitation events (e.g., 95th percentile) inmore regions than those with statistically significantdecreases, but strong regional and subregionalvariations in the trends. [Regional details in Table 3-2]Likely anthropogenic influence ontrends in warm/cold days/nights atthe global scale. No attribution oftrends at a regional scale with afew exceptions.Medium confidence thatanthropogenic influences havecontributed to intensification ofextreme precipitation at the globalscale.Virtually certain decrease in frequency and magnitudeof unusually cold days and nights at the global scale.Virtually certain increase in frequency and magnitudeof unusually warm days and nights at the global scale.Very likely increase in length, frequency, and/orintensity of warm spells or heat waves over most landareas. [Regional details in Table 3-3]Likely increase in frequency of heavy precipitationevents or increase in proportion of total rainfall fromheavy falls over many areas of the globe, in particularin the high latitudes and tropical regions, and inwinter in the northern mid-latitudes. [Regional detailsin Table 3-3]Winds(Section 3.3.3)Low confidence in trends due to insufficient evidence.Low confidence in the causes oftrends due to insufficient evidence.Low confidence in projections of extreme winds (withthe exception of wind extremes associated withtropical cyclones).PhenomenaRelated toWeather andClimateExtremesMonsoons(Section 3.4.1)El Niño andother Modes ofVariability(Sections 3.4.2and 3.4.3)Low confidence in trends because of insufficientevidence.Medium confidence in past trends toward morefrequent central equatorial Pacific El Niño-SouthernOscillation (ENSO) events.Insufficient evidence for more specific statements onENSO trends.Likely trends in Southern Annular Mode (SAM).Low confidence due to insufficientevidence.Likely anthropogenic influence onidentified trends in SAM. 1Anthropogenic influence on trendsin North Atlantic Oscillation (NAO)are about as likely as not. Noattribution of changes in ENSO.Low confidence in projected changes in monsoons,because of insufficient agreement between climatemodels.Low confidence in projections of changes in behaviorof ENSO and other modes of variability because ofinsufficient agreement of model projections.TropicalCyclones(Section 3.4.4)ExtratropicalCyclones(Section 3.4.5)Low confidence that any observed long-term (i.e., 40years or more) increases in tropical cyclone activity arerobust, after accounting for past changes in observingcapabilities.Likely poleward shift in extratropical cyclones.Low confidence in regional changes in intensity.Low confidence in attribution ofany detectable changes in tropicalcyclone activity to anthropogenicinfluences (due to uncertainties inhistorical tropical cyclones record,incomplete understanding ofphysical mechanisms, and degreeof tropical cyclone variability).Medium confidence in ananthropogenic influence onpoleward shift.Likely decrease or no change in frequency of tropicalcyclones.Likely increase in mean maximum wind speed, butpossibly not in all basins.Likely increase in heavy rainfall associated withtropical cyclones.Likely impacts on regional cyclone activity but lowconfidence in detailed regional projections due to onlypartial representation of relevant processes in currentmodels.Medium confidence in a reduction in the numbers ofmid-latitude storms.Medium confidence in projected poleward shift ofmid-latitude storm tracks.Impacts onPhysicalEnvironmentDroughts(Section 3.5.1)Medium confidence that some regions of the worldhave experienced more intense and longer droughts,in particular in southern Europe and West Africa, butopposite trends also exist. [Regional details in Table3-2]Medium confidence thatanthropogenic influence hascontributed to some observedchanges in drought patterns.Low confidence in attribution ofchanges in drought at the level ofsingle regions due to inconsistentor insufficient evidence.Medium confidence in projected increase in durationand intensity of droughts in some regions of theworld, including southern Europe and theMediterranean region, central Europe, central NorthAmerica, Central America and Mexico, northeastBrazil, and southern Africa.Overall low confidence elsewhere because ofinsufficient agreement of projections.[Regional details in Table 3-3]Floods(Section 3.5.2)Limited to medium evidence available to assessclimate-driven observed changes in the magnitudeand frequency of floods at regional scale.Furthermore, there is low agreement in this evidence,and thus overall low confidence at the global scaleregarding even the sign of these changes.High confidence in trend toward earlier occurrence ofspring peak river flows in snowmelt- and glacier-fedrivers.Low confidence that anthropogenicwarming has affected themagnitude or frequency of floods ata global scale.Medium confidence to highconfidence in anthropogenicinfluence on changes in somecomponents of the water cycle(precipitation, snowmelt) affectingfloods.Low confidence in global projections of changes inflood magnitude and frequency because of insufficientevidence.Medium confidence (based on physical reasoning)that projected increases in heavy precipitation wouldcontribute to rain-generated local flooding in somecatchments or regions.Very likely earlier spring peak flows in snowmelt- andglacier-fed rivers.Continued next page119