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

172 R. J. Nicholls et al.
land loss (×10 6 km 2 )
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2000
2025 2050
year
2075 2100
Figure 2. Global dryland losses according to the DIVA model assuming no adaptation for a 0.5 m
(grey lines) and a 2.0 m (black lines) rise in sea level by 2100.
(b) The pessimist’s versus the optimist’s view
Results for a world where adaptation is not implemented/fails versus a world
with successful adaptation are now contrasted for selected parameters.
Assuming no adaptation, of the two land-loss mechanisms considered in
DIVA, submergence is a much larger contribution to the loss than erosion.
Under these conditions, land loss amounts to a total of 877 000–1 789 000 km 2
for a 0.5 and 2.0 m rise in sea level, respectively (figure 2). This amounts to
approximately 0.6–1.2% of the global land area. The net population displaced
by this rise is more significant, being estimated at 72 and 187 million people
over the century, respectively (roughly 0.9–2.4% of the global population). This
reflects the high population density in coastal areas. 6 The results are consistent
with the literature on environmental refugees (e.g. [75]), which forecasts large
population displacements owing to sea-level rise. Most of the threatened people
are concentrated in three regions in Asia: east, southeast and south Asia
(figure 3). Given 0.5–2 m rise in sea level, a total of 53–125 million people are
estimated to be displaced over the century from these three regions alone. In
the three small-island regions (Caribbean, Indian Ocean and Pacific Ocean),
1.2–2.2 million people are displaced over the century, with all three regions
contributing significantly. It is noteworthy that impacts in some regions such
as north and west Europe and the North America Atlantic Coast, impacts are
much greater for a 2.0 m scenario than for a 0.5 m scenario. This reflects that
pre-existing defences provide benefits for a 0.5 m rise, but are overwhelmed
by a 2.0 m rise.
6 Note that the socioeconomic scenarios used here assume no coastward migration: if coastward
migration does continue in the coming decades, the impact potential would be amplified.
Phil. Trans. R. Soc. A (2011)
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