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1
Estimating the Global Damages from Climate Change
Joel Smith
and
Sam Hitz
Stratus Consulting Inc.
October 23, 2002
2
Objective
• Effort to identify benefits from different greenhouse gas emissions policies key issue is identification of marginal benefits
(avoided damages); are they: constant decreasing reverse sign?
provide useful input for examining long run goals
• Did not address the costs of mitigation
3
Overview
• We surveyed published sectoral studies that quantify the global impacts of climate change. Limited ourselves to global studies; did not examine regional impacts
literature
• Characterized the relationships between climate change and impacts based on studies results increasing impacts parabolic
indeterminate • Identified key factors and assumptions in these studies that
could substantially affect results inclusion and correctness
4
Methodology and Approach
• Global mean temperature (GMT) used as indicator of climate change recognize the many caveats with doing so
• Use equilibrium (generally older studies) and transient (generally newer studies) results
• Used metrics employed by authors of individual studies. No attempt to aggregate.
• Identified and analyzed key factors, assumptions and framework upon which studies were based.
5
Sectors Impacted by Climate Change
Published Studies
• Agriculture
• Sea Level Rise
• Water Resources
• Human Health
• Terrestrial Ecosystems
• Forestry
• Marine Ecosystems
• Biodiversity
• Energy
No Global Studies
• Recreation and Tourism
• Transport
• Building
• Insurance
• Human Amenity
• Mitigation
6
Presentation
• Results from agriculture, coastal resources, biodiversity and water sector are representative of these categories.
7
AgricultureRosenzweig et al., 1995
Percent Change in Number of People at Risk of Hunger (2060)
-20
-10
0
10
20
30
40
50
0 1 2 3 4 5 6
°C
% c
han
ge
in n
um
ber
of
peo
ple
Level 2 Farm AdaptationLevel 1 Farm AdaptationLow Temp. No Farm Adaptation
GISS
GFDL
UKMO641 million people at risk in 2060 Reference Scenario
GFDL
GISS
UKMO
Adaptation Level 1:Shifts in planting date (+/- 1 month)Additional application of irrigation water to crops already under irrigationChanges in crop variety to currently available varieties
Adaptation Level 2:Large shifts in planting date (>1month)Increased fertilizer applicationInstallation of irrigation systemsDevelopment of new crop varieties
GISS-A2030
8
AgricultureParry et al., 1999
Percent Change in Number of People at Risk of Hunger
0
10
20
30
40
50
60
0 0.5 1 1.5 2 2.5 3 3.5
°C
Per
cen
t ch
ang
e in
nu
mb
er o
f p
eop
le a
t ri
sk
HadCM2
HadCM3
2020s443 ppmv CO2
2020s441 ppmv CO2
2050s527 ppmv CO2
2050s565 ppmv CO2
2080s642 ppmv CO2
2080s731 ppmv CO2
250 million people at risk of hunger in reference scenario.
9
Agriculture Conclusions
• Results suggest initial benefits that eventually decrease and give way to damages as GMT rises, or alternatively, initial damages that decrease before continually rising.
• Some disagreements at lower temperatures, but eventually increasing damages beyond 3-4° C.
• This result agrees with expectation based on underlying biophysical processes.
10
Coastal ResourcesFankhauser, 1995.
Cost of Sea Level Rise in OECD Countries
0
500
1000
1500
2000
20 200
Sea level rise by 2100 (cm)
Bill
ion
s $
100
11
Coastal ResourcesNicholls et al., 1999
Additional People in the Hazard Zone as a Function of SLR
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30 35 40 45
Sea level rise (cm)
Ad
dit
ion
al p
eop
le (
mill
ion
s)
HadCM2
HadCM3
2020s
2050s
2080s
12
Coastal Resources Conclusions
• Damages seem to increase linearly with SLR.
• This result is in line with expectations of monotonically rising costs.
• These costs likely to continue accruing well into the next century, as sea level continues to rise, even after CO2 stabilizes.
13
BiodiversityHalpin, 1997.
Percent Change in Eco-Climatic Classes for Biosphere Reserves Compared to Global Average
0
10
20
30
40
50
60
70
80
90
0 1 2 3 4 5 6
°C
% o
f ar
ea w
her
e ec
o-c
limat
ic c
lass
ch
ang
e o
ccu
rs
Biosphere Reserves
Total Terrestrial Area
OSU
GFDL
GISS
UKMO
14
Biodiversity
• Eco-climatic classes change within global bio-reserves with greater frequency as GMT rises.
• There is little reason to doubt this result. It would be difficult to argue that climate change will slow the loss of threatened species.
• This is mentioned because even loss of individual species or ecosystems could be motivation for mitigation.
15
Water ResourcesArnell, 1999.
Change in Number of People in Countries in Water Stress
-100
-50
0
50
100
150
0 0.5 1 1.5 2 2.5 3 3.5
°C
Nu
mb
er o
f p
eop
le (
mill
ion
s)
HadCM2/GGax
HadCM3/GGa1
2020s
2050s
2080s
16
Water ResourcesArnell, 1999.
Difference Between Total Population in Countries Where Water Stress Increases and Countries Where Water Stress Decreases
-3000
-2500
-2000
-1500
-1000
-500
0
500
1000
1500
0 0.5 1 1.5 2 2.5 3 3.5
°C
Nu
mb
er o
f p
eop
le (
mill
ion
s)
HadCM2/GGax
HadCM3/GGa1
2020s2050s
2080s
17
Water Resources Conclusions
• No clear relationship between climate change and impacts on water resources.
• Averaging at the regional or country level presents problems. Basin level is more appropriate.
• We think there should be increasing damages with increasing GMT. Not (yet) borne out by published literature.
18
Aggregate Studies
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
0 1 2 3 4 5 6
Global Mean Temperature (°C)
Percen
t o
f W
orld
GD
P))
)
Mendelsohn, output
Nordhaus, output
Nordhaus, population
Tol, output
Tol, equity
19
Table 6. Summary of sectoral damage relationships with increasing temperature.
Sector Increasing damagesa Parabolic Unknown
Agriculture X
Coastal X
Water X
Health X
Terrestrial ecosystem productivity X
Forestry X?b
Marine ecosystems X?c
Biodiversity X
Energy X
Aggregate X
a. Increasing damages means there are damages with small increases in GMT, and the damages increase with higher GMTs. We are unable to determine whether the damages
increase linearly or exponentially with GMT. b. We believe this is parabolic, but with only one study it is difficult to ascertain temperature
relationship, so there is uncertainty about this relationship. c. This relationship is uncertain because there is only one study on this topic.
Sectoral Damage Relationships
20
Limitations
• Did not consider: impacts of temperature changes in excess of 1.4 to 5.8° C
range considered likely by Houghton et al.,2001 change in climate variability impacts due to long term (i.e. post 2100) climate change potential large scale singular events (e.g. collapse of THC or
WAIS) interaction among impacts on different sectors (e.g. water
and agriculture) ancillary benefits and proactive adaptation.
21
Limitations
• Also: Adaptation generally handled with simplistic
assumptions can over or underestimate impacts
Assumptions about population and development not consistent development can make substantial difference in
vulnerability of societal sectors
22
Conclusions
• In all sectors, the results point to increasing damages beyond a temperature range of 3-4°C.
• Below this critical temperature range, the picture is much less clear. In some sectors damages may accrue immediately and continue to grow. In others, benefits may eventually give way to damages or initial damages may decrease before steadily increasing.
• Aggregate studies we examined, tend to confirm this basic conclusion.
23
Final Caveats
• Changes in the key assumptions and simplifications upon which each of the studies depend could either lower or raise this critical temperature range.
(e.g. adaptation, development, treatment of variability, interaction among sectors, long-term temperature change or changes in the climate system)
• We should expect significant variation among regional results. The critical temperature range we identify could be quite different depending on the particular combination of region and sector.