Four degrees and beyond: the potential for a global ... - Amper

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184 F. Gemenne (a) Extreme weather events Extreme weather events include heat waves, tropical cyclones, droughts and flooding. The latest Intergovernmental Panel on Climate Change (IPCC) report predicts, by the end of this century, a ‘very likely increase in hot extremes, heat waves and heavy precipitation’, a ‘likely increase in tropical cyclone activity’, with ‘less confidence in the decrease of tropical cyclone numbers’, as well as ‘very likely precipitation increases in high latitudes and likely decreases in most subtropical land regions’ [15]. In addition, it is expected that annual run-off and precipitation will increase in high latitudes, whereas water resources will decrease in mid-latitudes and in the tropics, as well as in arid regions. The IPCC notes that the increases in both droughts and tropical cyclone activity present a potential for population migration [16]. The latter claim, however, can be disputed, as the impacts of extreme weather events on migration flows are diverse and sometimes controversial. Disasters can indeed result in highly diverse patterns of displacement. For example, it is widely thought that disasters are more likely to induce temporary displacement, allowing people to return home once the danger is gone. As a result of this assumption, people forced to flee to another country because of a disaster have often been granted temporary protection status: for example, temporary protection status in the USA was granted to the people of Montserrat displaced by the volcanic eruption in 1997, and to the people of Honduras and Nicaragua displaced by Hurricane Mitch in 1998. The experience of Hurricane Katrina, however, showed that people displaced by natural disasters were not always able to go home, as a significant proportion of the population of New Orleans has still not returned, and seems unlikely to do so in the future [17]. It is now increasingly acknowledged that disasters result in both temporary and permanent displacement, as well as in both proactive and reactive displacement. It is likely that an increase in extreme weather events will result in an increase in the number of natural disasters [18]. This would reinforce the upward trend in the occurrence of disasters, identified since the start of their systematic recording in the early twentieth century [19]. Until now, this upward trend has been primarily explained by the increased vulnerability of the affected populations. A disaster occurs when natural risk meets vulnerability [20]: if the number of natural risks increases with a temperature rise, the number of disasters will consequently increase unless the vulnerability of populations can be reduced. Unless robust adaptation strategies are implemented, there is no sign that vulnerability might decrease in the near future. In a 4 ◦ C+ world, however, the main driver of natural disasters might shift from an increase in vulnerability to an increase in the number and severity of natural events. In addition, the characteristics of these events themselves might change, as different hazards could combine with each other in an unprecedented setting. This could affect both the location of disasters and the design and implementation of disaster-reduction policies. (b) Sea-level rise The most obvious consequence of climate change with regard to environmental migration is probably sea-level rise. Though sea-level rise will not be uniform across the globe, some studies suggest that the rise could be about 1 m by the end of the century [21,22]. The IPCC notes that [23]: Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010
Climate-induced population displacements 185 Many millions more people are projected to be flooded every year due to sea-level rise by the 2080s. Those densely-populated and low-lying areas where adaptive capacity is relatively low, and which already face other challenges such as tropical storms or local coastal subsidence, are especially at risk. The numbers affected will be largest in the mega-deltas of Asia and Africa while small islands are especially vulnerable. Unlike extreme weather events, sea-level rise is more predictable in the longer term, and populations at risk can be more easily identified, which facilitates the implementation of adaptation plans. Given that coastal and deltaic areas are usually very densely populated, the potential for large numbers of migrants is particularly high [24,25]. The projection of sea-level rise is usually based on a 2 ◦ C average temperature increase. In a world with a 4 ◦ C+ temperature increase, sealevel rise would be higher, especially with the increased probability of the deglaciation of the Greenland and West Antarctic ice sheets [26]. Sea-level rise would also induce greater coastal erosion, as well as bigger storm surges. The El Niño–Southern Oscillation could also be affected, magnifying the differences in local sea-level rises. It is especially important to understand and forecast local sea-level rises, as the associated migration potential depends on the local sea-level rise rather than the average one. In that regard, a 4 ◦ C+ temperature increase would increase not only the average sea-level rise, but also—and probably more importantly—the uncertainties associated with the migration potential. (c) Water stress Water stress will be caused by a series of cumulative factors: droughts, salt water intrusion due to sea-level rise, and also the melting of mountain glaciers in the long run. The IPCC forecasts that ‘freshwater availability in Central, South, East and Southeast Asia, particularly in large river basins, is projected to decrease due to climate change which, along with population growth and increasing demand arising from higher standards of living, could adversely affect more than a billion people by the 2050s’ [23]. The water supplies stored in glaciers and snow cover are also expected to decline, reducing freshwater availability in regions supplied by melt-water from mountain ranges. The situation is expected to be most difficult in Africa, where an estimated 75 million to 250 million people will be at risk of water stress due to climate change by 2020. Given that this water stress will be associated with higher demand, especially in big cities, water-related problems are very likely to be exacerbated [27]. The effects of water stress on migration patterns remain heavily contested: some authors argue that droughts and desertification are a major push factor for migration [28,29], 1 while others contend that people affected by droughts 1 Hammer [28] argues that one million people were displaced as a result of the 1985 drought in Niger, and that ‘hundreds of thousands of people from rural Sahel regions are displaced every year as a consequence of environmental change and desertification’. Leighton [29] makes a similar case for Northeast Brazil. Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010
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ISSN 1364-503X volume 369 number 19
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Phil. Trans. R. Soc. A (2011) 369,
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Editorial David Garner Phil. Trans.
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Four degrees and beyond: the potent
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Preface 5 commitments might give us
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8 M. New et al. In the final plenar
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10 M. New et al. supports the messa
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12 M. New et al. Table 1. Impacts a
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14 M. New et al. actors (NNSAs)—r
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16 M. New et al. as permanent crop
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18 M. New et al. 24 Boe, J. L., Hal
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Beyond 'dangerous' climate change:
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Beyond dangerous climate change 21
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(i) Energy and industrial process e
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(a) 50 (b) GtCO 2e yr -1 40 30 20 1
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Table 1. Summary of scenario pathwa
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Cumulative carbon emissions, emissi
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46 N. H. A. Bowerman et al. althoug
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48 N. H. A. Bowerman et al. a likel
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50 N. H. A. Bowerman et al. (b) Mod
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52 N. H. A. Bowerman et al. In most
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emissions (GtC) Review. Global warm
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global surface warming (°C) 6 5 4
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temperature (relative to 1861-1890
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°C above pre-industrial 8 7 6 5 4
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Water availability in +2 ◦ C and
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(ii) Water stress index Water avail
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(a) number of models, black line nu
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change in run-off (%) change in run
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118 P. K. Thornton et al. 1. Introd
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120 P. K. Thornton et al. increases
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122 P. K. Thornton et al. Table 1.
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124 P. K. Thornton et al. century.
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Editorial Editorial 3 D. Garner Pre
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