IPCC Report.pdf - Adam Curry

Chapter 3Changes in Climate Extremes and their Impacts on the Natural Physical Environmentand A2 scenarios). Regional changes in temperature extremes will often differ from the mean global temperaturechange. [3.3.1; Table 3-3; Figure 3-5]It is likely that the frequency of heavy precipitation or the proportion of total rainfall from heavy rainfallswill increase in the 21st century over many areas of the globe. This is particularly the case in the high latitudesand tropical regions, and in winter in the northern mid-latitudes. Heavy rainfalls associated with tropical cyclones arelikely to increase with continued warming induced by enhanced greenhouse gas concentrations. There is mediumconfidence that, in some regions, increases in heavy precipitation will occur despite projected decreases in totalprecipitation. For a range of emission scenarios (SRES A2, A1B, and B1), a 1-in-20 year annual maximum 24-hourprecipitation rate is likely to become a 1-in-5 to 1-in-15 year event by the end of the 21st century in many regions,and in most regions the higher emissions scenarios (A1B and A2) lead to a greater projected decrease in returnperiod. Nevertheless, increases or statistically non-significant changes in return periods are projected in some regions.[3.3.2; Table 3-3; Figure 3-7]There is generally low confidence in projections of changes in extreme winds because of the relatively fewstudies of projected extreme winds, and shortcomings in the simulation of these events. An exception ismean tropical cyclone maximum wind speed, which is likely to increase, although increases may not occur in all oceanbasins. It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged.There is low confidence in projections of small-scale phenomena such as tornadoes because competing physicalprocesses may affect future trends and because climate models do not simulate such phenomena. There is mediumconfidence that there will be a reduction in the number of mid-latitude cyclones averaged over each hemisphere dueto future anthropogenic climate change. There is low confidence in the detailed geographical projections of mid-latitudecyclone activity. There is medium confidence in a projected poleward shift of mid-latitude storm tracks due to futureanthropogenic forcings. [3.3.3, 3.4.4, 3.4.5]Uncertainty in projections of changes in large-scale patterns of natural climate variability remains large.There is low confidence in projections of changes in monsoons (rainfall, circulation), because there is little consensusin climate models regarding the sign of future change in the monsoons. Model projections of changes in El Niño-Southern Oscillation variability and the frequency of El Niño episodes as a consequence of increased greenhouse gasconcentrations are not consistent, and so there is low confidence in projections of changes in the phenomenon.However, most models project an increase in the relative frequency of central equatorial Pacific events (which typicallyexhibit different patterns of climate variations than do the classical East Pacific events). There is low confidence in theability to project changes in other natural climate modes including the North Atlantic Oscillation, the Southern AnnularMode, and the Indian Ocean Dipole. [3.4.1, 3.4.2, 3.4.3]It is very likely that mean sea level rise will contribute to upward trends in extreme coastal high waterlevels in the future. There is high confidence that locations currently experiencing adverse impacts such as coastalerosion and inundation will continue to do so in the future due to increasing sea levels, all other contributing factorsbeing equal. There is low confidence in wave height projections because of the small number of studies, the lack ofconsistency of the wind projections between models, and limitations in the models’ ability to simulate extreme winds.Future negative or positive changes in significant wave height are likely to reflect future changes in storminess andassociated patterns of wind change. [3.5.3, 3.5.4, 3.5.5]Projected precipitation and temperature changes imply possible changes in floods, although overall thereis low confidence in projections of changes in fluvial floods. Confidence is low due to limited evidence andbecause the causes of regional changes are complex, although there are exceptions to this statement. There is mediumconfidence (based on physical reasoning) that projected increases in heavy rainfall would contribute to increases inlocal flooding, in some catchments or regions. Earlier spring peak flows in snowmelt and glacier-fed rivers are verylikely. [3.5.2]There is medium confidence that droughts will intensify in the 21st century in some seasons and areas,due to reduced precipitation and/or increased evapotranspiration. This applies to regions including southern113