World in Transition: Climate Change as a Security Risk - WBGU

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58 5 Impacts of climate change on the biosphere and human society a -3000-1500-800 -250 b -500 -200 -50 -20 -50 0 50 250 800 1500 3000 [mm] 0 20 50 200 500 [mm] Figure 5.1-3 Climatic water balance: a) mean for the period 1961–1990. b) Change in climatic water balance based on observations in the period 1975–2004. Climatic water balance is the result of the difference between precipitation and potential evapotranspiration. Source: WBGU; data: Potsdam Institute for Climate Impact Research (PIK) climate database
1990. The basic pattern of the global water cycle is as follows: in the tropics, plenty of water evaporates due to the high temperatures, but due to the rising air mass near the equator (the Inter-Tropical Convergence Zone) it soon falls again as rain; these are the tropical cloud and rain-belts (e.g. Brazil, Congo, Indonesia). Evaporation of water is considerable in the subtropics, too, but precipitation is scant because sinking air masses mean that the air is dry and clouds are few. This is why the desert regions of the world are located in the subtropics: in the northern subtropics lies the Sahara, for example, while the Namibian and Australian deserts are in the southern subtropics. A large proportion of the moisture that evaporates in the subtropics is transported to middle and high latitudes and falls as rain there, so in these regions precipitation exceeds evaporation. An important aspect of the water cycle is the monsoon circulation, which causes highly seasonal precipitation in some regions of the world (e.g. southeast Asia); in some countries such as India and China, agriculture and food security depend on the monsoon rains. The monsoon winds and rains are driven by seasonally varying differences in temperature between land and sea. It is a strongly non-linear phenomenon that can be influenced both by aerosol pollution of the atmosphere and by global warming. The effects of global warming amplify this water cycle: evaporation in the subtropics increases, and this on average leads to heavier precipitation in the medium and high latitudes. There is already evidence from observations that this is indeed happening. In the subtropical areas of the Atlantic, salinity has been on the increase for decades, while in the high latitudes it is declining. In addition, long time series for Eurasian rivers flowing into the Arctic Ocean show that river flow has been increasing constantly for several decades, as is to be expected with an increase in rainfall in the high latitudes (Peterson et al., 2002). As a result, subtropical regions are tending to become more arid, while high-latitude regions are becoming more humid, although there are many regional and micro-regional idiosyncrasies in this regard (Fig. 5.1- 3b). In this way, many arid areas have become even drier in recent decades, especially in the Saharan and Mediterranean regions, southern Africa, the southwestern United States of America, north-eastern Brazil, India and the northern half of China. The reasons for this, however, are not always related to macro-climatic factors alone (e.g. Sahel: Zeng, 2003; Hutchinson et al., 2005), but also to human interventions in the environment at regional level, as mentioned above, some of which will be discussed in more detail later (Chapter 7 and Sections 6.2 and 6.3). Changes in climatic parameters 5.1 Model scenarios depict a clear pattern for the future (Fig. 5.1-4): the high-rainfall regions in the tropical rain belt and the middle to high latitudes will become even more humid overall, while the arid regions of the subtropics will become even drier. The models also single out the Mediterranean region and southern Africa in particular in terms of increasing aridity. For other regions, the projections are less robust; for the Sahel region, for example, different models project major changes, but with contradicting signs (IPCC, 2007a, b). With regard to precipitation, it is not just annual or seasonal amounts that are of concern, but also extreme weather events such as periods of drought and unusually intense rainfall. Both the data and the model calculations reveal a trend where an increasing share of annual rainfall is concentrated in such intense precipitation events (in other words occurring over a few days), accompanied by a simultaneous increase in the duration of periods without rainfall. This tendency increases both the risk of floods and the frequency of periods of drought. Based on one model scenario, Figure 5.1-5 shows the regions where a major increase in the risk of drought due to longer periods of dry weather is likely. Again, the regions most implicated in this are the Mediterranean area, southern Africa and Brazil, where drought also extends into the Amazon region. Another aspect of the drought is revealed (based on another model) by the projected dynamics of the climatic water balance (Fig. 5.1-6.). In most continental regions, even in areas where precipitation increases in absolute terms, the climatic water balance declines. There is thus less water available for human use, because the increase in evaporation exceeds the increase in precipitation. Figure 5.1-7, based on the same model simulations as those used in Figure 5.1-5, shows a rise in the incidence of extreme precipitation in most areas of the world. This increase is probably largely attributable to basic physics, as mentioned above, in other words to the fact that warmer air can hold more water vapour. 5.1.3 Tropical cyclones Since the extreme hurricane season of 2005, if not before, public interest has focussed increasingly on the risk posed by tropical cyclones. In recent decades a distinct increase in the intensity of tropical cyclones has been observed, probably due primarily to the increase in tropical ocean temperatures (Emanuel, 2005; Webster et al., 2005; Hoyos et al., 2006). The rise in tropical ocean temperatures has so far followed a 59
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Climate Change as a Security Risk G
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Members of the German Advisory Coun
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German Advisory Council on Global C
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VI Council Staff and Acknowledgment
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VIII Contents 3.3.2 Economic factor
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X Contents 6.5.4.1 Avoiding environ
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XII Contents 10.3.2 Climate policy
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Tables Table 2.2-1 Main differences
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XVI Figures Figure 8.1-2 Climate st
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XVIII Acronyms and Abbreviations FI
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A new security policy challenge Sum
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ilization, the collapse of social s
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Six threats to international stabil
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Page 38 and 39: 16 1 Introduction the present state
Page 41 and 42: Broadening the concept of security
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Page 78 and 79: 56 5 Impacts of climate change on t
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Figure 6.4-3 Conflict constellation
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A marked increase in social unrest
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6.4.3.2 Hurricane risks in the Gulf
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A Category Six hurricane hits Houst
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Box 6.5-1 Migration - definitions a
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Figure 6.5-1 Conflict constellation
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differing challenges to the societi
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Fictitious confrontation scenario:
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tions, this has already given rise
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programme that is making a signific
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conflict (Geissler, 1999; Phuong, 2
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132 7 Hotspots of climate change It
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134 7 Hotspots of climate change de
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136 7 Hotspots of climate change 7.
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138 7 Hotspots of climate change ex
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140 7 Hotspots of climate change re
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142 7 Hotspots of climate change (G
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144 7 Hotspots of climate change mo
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146 7 Hotspots of climate change im
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148 7 Hotspots of climate change in
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150 7 Hotspots of climate change Hu
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152 7 Hotspots of climate change In
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154 7 Hotspots of climate change ra
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156 7 Hotspots of climate change GD
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158 8 Climate change as a driver of
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178 9 Research recommendations Tipp
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180 9 Research recommendations toge
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182 9 Research recommendations 2020
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184 9 Research recommendations ture
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186 9 Research recommendations wate
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188 9 Research recommendations tion
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190 10 Recommendations for action t
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192 10 Recommendations for action b
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194 10 Recommendations for action f
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196 10 Recommendations for action a
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198 10 Recommendations for action d
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200 10 Recommendations for action A
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204 10 Recommendations for action s
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206 10 Recommendations for action G
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208 10 Recommendations for action 1
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212 10 Recommendations for action n
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Abel, W (1974) Massenarmut und Hung
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BMU (Bundesministerium für Umwelt,
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36. University Amsterdam, Faculteit
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for Action. Global Commission on In
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library.fes.de/pdf-fi les/stabsabte
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- a review’. In Kreimer, A, Arnol
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ics in the Southern Brazilian Amazo
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No. 113. UNHCR Evaluation and Polic
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Stockle, C O, Dyke, P T, Williams,
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WBGU (German Advisory Council on Gl
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Action Plan ‘Crisis Prevention’
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er countries in 2001 at the 4th Min
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focuses on the security needs of hu
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towards the future as plausible ‘
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Index A Aceh 107 Africa 70-71, 72,
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Framework Convention on Climate Cha
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208, 211 security strategies 19, 21
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World in Transition: Climate Change as a Security Risk - WBGU

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