mine how climate might change in response to greenhouse
gas (GHG) accumulation in the upper atmosphere. The Intergovernmental Panel on Climate Change (IPCC) has a process
SUMMARY | APRIL 2010
by which teams submit models for use in IPCC assessment
reports. Assessment Report 4 (AR4) incorporated 24 models,
whereas Assessment Report 5 (AR5) included 61 models. The
analysis presented in this policy note is based on the following four AR5 models:
Table 3. Rainfall in the driest three months by region, 1950–2000
Percentile
5th
25th
50th
75th
95th
1. Luzon
27
60
135
244
410
1.1 Luzon
27
55
130
248
416
1.2 CAR
32
106
156
226
326
2. Visayas
110
193
251
444
571
3. Mindanao
235
300
374
473
619
3.1 Mindanao
229
303
386
492
624
3.2 ARMM
257
284
315
388
422
Total
32
129
256
383
562
Source: Constructed by authors based on WorldClim version 1.4
(Hijmans et al. 2005).
Region
1. GFDL-ESM2M, which was developed by the National
Oceanographic and Atmosphere Administration’s
General Fluid Dynamics Laboratory (GFDL) (Dunne et
al. 2012, 2013)
Figure 5. Mean daily maximum temperature in the warmest
month, 1950–2000
2. HadGEM2-ES, the Hadley Centre Global Environmental Model (HadGEM), from the Met Office Hadley
Centre (Collins et al. 2011; Martin et al. 2011)
3. IPSL-CM5A-LR, generated by Institut Pierre-Simon Laplace (IPSL) (Dufresne et al. 2013)
4. MIROC-ESM-CHEM, (MIROC), from the Japan Agency
for Marine-Earth Science and Technology, Atmosphere and Ocean Research Institute (University of Tokyo), and National Institute for Environmental Studies
(Sakamoto et al. 2012)
In AR5, each of the above-named models employed five different assumptions about GHG emissions, but the analysis in
this policy note is limited to the assumption of the highest
GHG emissions—Representative Concentration Pathway
(RCP) 8.5—which is most commonly used by researchers.
Projected changes in yearly precipitation from the 1950–
2000 baseline period to the climate in 2050 are shown in Figure 6, and are quantified by regional grouping in Table 5. All
of the models indicate that the Philippines will generally receive more rainfall; the median amount averaged across the
nation is 256 millimeters.
Source: Constructed by authors based on WorldClim
version 1.4 (Hijmans et al. 2005).
Table 4. Mean daily maximum temperature in the warmest
month by region, 1950–2000
Percentile
5th
25th
50th
75th
95th
1. Luzon
25.3
28.7
30.2
30.7
31.5
1.1 Luzon
26.5
29.2
30.3
30.8
31.5
1.2 CAR
21.4
24.5
27.6
29.9
30.8
2. Visayas
27.9
29.5
30.2
30.6
31.3
3. Mindanao
25.5
28.4
30.0
30.8
31.8
3.1 Mindanao
25.6
28.4
30.0
30.7
31.7
3.2 ARMM
25.2
28.1
30.5
31.5
32.1
Total
25.7
28.9
30.1
30.7
31.5
Source: Constructed by authors based on WorldClim version 1.4
(Hijmans et al. 2005).
Region
While the averages from the climate models do not differ
greatly for the country as a whole, regional differences are
substantial. The most obvious of these are the significantly
drier portion of CAR and western Luzon under the GFDL
model, and the significantly drier portion of Mindanao (most
of central and south) and ARMM under the HadGEM model
(which also has a modestly drier portion in western Luzon). It
should be noted that these significantly drier areas are likely
to influence the model results in their respective areas.
PROJECTED DIFFERENCES AMONG REGIONS UNDER CLIMATE CHANGE
General circulation models (GCMs), also known as global climate models, are developed by climate scientists to deter3