Part II Climate Change, Its Impact and Adaptation
Chapter 3 Climate Change and Its Impact: A Review of Existing Studies 21 A. Introduction
C. Projected Climate Change in Southeast Asia
For the four countries—Indonesia, Philippines, Thailand, and Viet Nam—
under B2, total population is projected to increase from 364 million in 1990 to 652 million (17% aged 60+) by 2050 and then decline to 628 million (24%
aged 60+) by 2100 (Tables 4.2 and 4.3). Under A1FI, total population would increase to 603 million (24% aged 60+) by 2050 and then decline to 415 million (41% aged 60+) by 2100. Both scenarios project large increases in urban population, from 37% in 1990 to 89% by 2100 (Table 4.3).
The region’s mean temperature toward the end of this century is projected to increase 2.5°C under B2 and 4.8°C under A1FI, over 1990, without global mitigation.
Overall, the projected increases in mean temperature under the B2 and A1FI scenarios are in line with the projected increases in global mean temperature (Figure 4.4). Under the B2 reference scenario, the projected increase would range from 2.41°C to 2.62°C by 2100. Under A1FI, the increase would be more significant, ranging from 4.61°C to 5.0°C by the end of this century. By 2100, average annual temperatures in western Southeast Asia will be hotter than the eastern part of the region.
Table 4.3 Population Aged 65 Years and above and Urban Population in the Four Countries
Reference Scenario 1990 2020 2050 2100
Proportion of population aged 65 years and above (%)
B2 6 11 17 24
A1FI 6 13 24 41
Proportion of urban population (%)
B2/A1FI 37 48 70 89
Sources: The proportion of elderly population in B2 was projected by the United Nations (1998); in A1FI by the International Institute for Applied Systems Analysis (IIASA 1996). The estimated proportion of the urban population up to 2030 was derived from United Nations estimates (UN 2004). In the absence of any estimate beyond 2030, it was assumed that from 2030 to 2050 the rate of increase continues. After 2050, the rate of increase is assumed to halve every 25 years (Tol 2004).
Table 4.2. Population Growth and Economic Growth under B2 and A1FI
Country Population (million) GDP (billion $/year)
1990 2020 2050 2100 1990 2020 2050 2100
B2 Scenario
Indonesia 182 264 318 302 122 730 2,455 5,845
Philippines 61 100 131 124 58 308 1,036 2,466
Thailand 55 68 73 69 98 594 2,000 4,762
Viet Nam 66 104 130 133 12 86 248 553
Total 364 536 652 628 289 1,718 5,740 13,626
A1FI Scenario
Indonesia 193 262 297 209 122 1,020 5,636 19,891
Philippines 64 101 121 83 58 491 2,711 9,568
Thailand 58 75 81 64 98 819 4,524 15,966
Viet Nam 65 95 104 59 12 124 551 1,586
Total 380 533 603 415 289 2,454 13,422 47,012
Note: Since there is no country-specific data available beyond 2100 for Southeast Asia, for the B2 scenario, population growth up to 2150 was estimated by multiplying the country population in 2100 by the ratio of regional population in 2150 relative to the level in 2100. For the A1FI scenario beyond 2100, the population was extrapolated based on the assumption that the population growth rate up to 2125 is equivalent to half that in the period from 2075 to 2100, and declines by half again every 25 years after 2125.
Sources: For both scenarios, the country-level population projection was taken from the Center for International Earth Science Information Network database (CIESIN 2002). The regional population up to 2150 was obtained from the population projections developed by the United Nations (1998), which are consistent with the IPCC (2000) B2 scenario.
Chapter 4: Modeling Climate Change and Its Impact 69
With stabilization under the most pessimistic scenario, the projected mean temperature increase in Southeast Asia by 2100 would be substantively lower at only 2.3ºC at 550 ppm and only 1.8 ºC at 450 ppm, relative to 1990.
With S550, under B2, the mean temperature increase by 2100 would range from 1.85°C to 2.0°C relative to the 1990 temperature level. Under A1FI, the corresponding increase would range from 2.18°C to 2.36°C. With S450, the projected mean temperature increase by 2100 would be less, ranging from 1.36°C to 1.45°C under B2 and 1.69°C to 1.82°C under A1FI.
Among the four countries, Thailand would experience the highest increase in mean temperature and the Philippines the lowest.
Indonesia, Thailand, and Viet Nam will experience increasingly drier weather conditions in the next 2–3 decades, although this trend is projected to reverse by mid-century.
The modeling results show that, by 2050, with the exception of the Philippines, the decrease in precipitation from the 1990 level will range from 0.20 mm/day to 0.34 mm/day under the B2 scenario, and from 0.11 mm/
day to 0.26 mm/day under A1FI (Figure 4.5).
By 2100, the trend in precipitation will be reversed, with most countries experiencing an increase in precipitation. Under the B2 scenario, Indonesia would experience an increase in precipitation of 0.22 mm/day from its 1990 level, while all the other countries would see a decrease in precipitation from the 1990 level ranging from 0.05 mm/day to 0.16 mm/day. Under the A1FI scenario, on the other hand, most countries would experience an increase in precipitation, ranging from 0.09 mm/day to 1.14 mm/day. In general, by the end of this century, it is projected that precipitation will likely be higher than the 1990 precipitation level.
Figure 4.4. Annual Average Temperature Increase Relative to 1990 in the Four Countries
Source: ???.
A1FI
1990 2000 2010
2020 2030 2040 2050 2060 2070
2080 2090 2100 A1FI Reference A1FI S550 A1FI S450 B2
1990 2000 2010
2020 2030 2040 2050 2060 2070
2080 2090 2100
B2 Reference B2 S550 B2 S450
Temperature rise (°C)
0 1 2 3 4 5 6
Temperature rise (°C)
0 1 2 3 4 5 6
Source: ADB study team.
The Economics Of Climate Change in Southeast Asia: A Regional Review
70
Precipitation patterns appear little different under the two scenarios and stabilization cases before 2050, but become significantly different after, underscoring the difficulty of predicting precipitation.
The change in precipitation under the scenarios (B2 or A1FI) appears similar to the stabilization cases (S550 or S450) before 2050 (Figure 4.5).
Beyond 2050, however, the change in precipitation with stabilization would be very different than without it. For example, Indonesia would experience an increase in precipitation of 0.22 mm/day without stabilization by 2100 under B2; with S550, on the other hand, the country would experience no change in precipitation from its 1990 level. This makes clear that predicting precipitation is more difficult and challenging than predicting temperature.
Figure 4.5. Annual Average Precipitation Change Relative to 1990 in the Four Countries
2050
A1FI Reference A1FI S550 A1FI S450 2050
B2 S550 B2 S450
Precipitation change (mm/day) Precipitation change (mm/day)
2100 2100
Precipitation change (mm/day) Precipitation change (mm/day)
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
Indonesia Philippines Thailand Viet Nam
Indonesia Philippines Thailand Viet Nam
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
B2 Reference
A1FI Reference A1FI S550 A1FI S450
B2 S550 B2 S450
Indonesia Philippines Thailand Viet Nam
Indonesia Philippines Thailand Viet Nam B2 Reference
Note: The scale used for B2 is smaller than A1FI to emphasize the difference in precipitation changes.
Source: ADB study team.
Chapter 4: Modeling Climate Change and Its Impact 71