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Climate Change impacts for
emission paths that peak and
decline
Authors: Chris Hope,
Judge Business School, University of Cambridge
Rachel Warren, Tyndall Centre, School of
Environmental Sciences, University of East Anglia,
Norwich NR4 7TJ
Jason Lowe, MetOffice Hadley Centre (Reading Unit),
Department of Meteorology, University of Reading,
Reading, RG6 6BB
and the AVOID WS1 Team
AVOID is funded by the Department of Energy and Climate Change and the Department for Environment, Food and Rural Affairs
The Scenarios
• Emission scenarios: varied year in which
emissions peak globally, the rate of
emission reduction (R), and the minimum
level to which emissions are eventually
reduced (H or L).
• Focused on 2015-2044 (centred on 2030)
2035-2064 (centred on 2050)
2070-2099 (centred on 2085)
Scenarios: A1B, and policy scenarios
• 2030.R2.H, 2030.R5.L,
• 2016.R2.H, 2016.R4.L and 2016.R.Low
Percentage Emission Changes Relative to 1990
in the reference and policy scenarios
Percentage change in emissions of
CO2 equivalents relative to 1990
150%
100%
A1B Hadley
2030.R2.High
2030.R5.Low
50%
0%
2000
2016.R2.High
2016.R4.Low
2050
-50%
-100%
Year
2100
2016.R5.Low
Temperature implications: Jason Lowe’s
analysis showed that …
Probability Year
…
A1B
2016.R
2030.R
(2%H,
4%L, 5%L)
(2%H,
5%L)
of
remaining
below 2
degrees
2100
1%
30, 43,
45%
7, 17%
of
remaining
below 3
degrees
2100
1%
87, 91,
91%
63, 76%
of
remaining
below 4
degrees
2100
46%
98, 99,
99%
93, 96%
Temperature implications
Jason Lowe’s work told us:
• Under A1B temperatures are likely to reach 34C
• 2030 peaking insufficient for 2C and have
chance of 1 in 3 to 4 of exceeding 3C
• 2016 targets effective at avoiding 3C, chance
of exceeding falls to 1 in 10
• Only most stringent R=5% 2016 scenario has
45% chance to meet 2C target
• All avoid temperatures reaching 4 degrees
with high confidence (>=98%) except for 2030
2% L which leaves a 7% chance of more than
4C.
The earlier the peak in emissions, the
greater the avoided impacts
% of impacts avoided
% of impacts avoided
80
70
60
50
40
30
20
10
2016-5-L
Cooling
requirements
Soybean
productivity
Decreased
crop
suitability
Coastal
mangrove
Coastal flood
risk
Fluvial flood
risk
Increased
water
scarcity
0
2030-5-L
AVOID is funded by the Department of Energy and Climate Change and the Department for Environment, Food and Rural Affairs
The earlier the peak in emissions, the
greater the avoided impacts
% change in flood risk
Change in fluvial flood risk
300
250
200
150
100
50
0
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
Year
A1b
2016-2-H
2030-5-L
2030-2-H
2016-4-L
2016-5-L
2100
5000.0%
4000.0%
3000.0%
10th percentile
50th percentile
2000.0%
90th percentile
1000.0%
o
m
iti
ga
tio
n
20
20
50
16
R
20
20
50
30
N
o
R
m
20
iti
ga
50
tio
n
21
20
00
16
R
21
20
00
30
R
21
00
0.0%
N
Flooding increase
Global coastal flood plain population in the 2020s,
2050s and 2080s under the different sea-level rise
scenarios
Net global losses of saltmarsh by the
2080s due to sea-level rise, including
uncertainty
Saltmarsh loss
50.0%
40.0%
30.0%
10th percentile
50th percentile
90th percentile
20.0%
10.0%
0.0%
No
mitigation
2016.R
2030.R
Key message: Date at which
emissions peak critical
• Example: water stress: by the 2080s, the 2016R
scenarios remove 38-41% of the increases in
water stress forcecast under A1B (HadCM3 50%
outcome) whereas the 2030R scenarios remove
only 33%.
• Example, coastal zone: avoided impacts in terms
of people experiencing coastal flooding are large,
about 43% by the 2080s in the 2016.R scenarios,
where in the 2030.R scenarios it is 30%.
• Example, biodiversity: 55-77% of climate change
induced extinction risks in European plants
avoided in 2016R scenarios compared to 44%
under 2030.R
Date at which
emissions peak critical
• Avoided impacts resulting from reducing
emissions from A1B scenario to 2016R
scenarios are greater than for the 2030R
scenarios
• …in all three of the sectors: water stress, coasts,
biodiversity
• Hence date at which emissions peak is more
important than the rate of subsequent emissions
reduction in determining the avoided impacts
Scope of the PAGE2002 model
• The major greenhouse gases.
• Economic, non-economic and catastrophic impacts.
• Time horizon of 2200.
• Probabilistic calculations
•Eight world regions
Inputs to PAGE model
• Emissions of greenhouse gases
• Atmospheric residence time of
greenhouse gases
• Sensitivity of the climate system
• Cooling effect of sulphates
• Impacts as a function of
temperature change
Inputs to the PAGE2002 model
• Discount rates and equity weights:
• The Stern runs used a ptp rate of 0.1% per year
and an EMUC of 1. Gives a mean discount rate
of about 1.5% per year, varying over time and
across regions.
• The AVOID runs used triangular distributions
for both. ptp rate of <0.1,1,2> % per year. EMUC
of <0.5,1,2>. Gives a mean discount rate of
about 3% per year
Structure of the PAGE2002 model
Select an abatement and adaptation policy
Global and
regional
temperature
Impacts
Costs of
abatement
Costs of
adaptation
Costs
The earlier the peak in emissions, the
greater the avoided impacts
Equity-weighted
Global Impacts
(year 2000) trillion US$
Economic benefits of avoided impacts
PAGE 2002
A1B
35
30
25
20
15
10
5
0
20
0
2
2016r2high
2030r2high
40
0
2
60
0
2
Year
80
0
2
00
1
2
PAGE-valued equity-weighted impacts under the
AVOID policy scenarios compared to the SRES
reference scenario A1B
A1B
9.00E+07
A1B 5%
8.00E+07
A1B 95%
2016r2high
Equity-weighted Global Impacts
(year 2000) million US$
7.00E+07
2016r2high 5%
6.00E+07
2016r2high 95%
2016r4low
5.00E+07
2016r4low 5%
4.00E+07
2016r4low 95%
2016r5low
3.00E+07
2016r5low 5%
2.00E+07
2016r5low 95%
2030r2high
1.00E+07
2030r2high 5%
0.00E+00
20
0
2
2030r2high 95%
40
0
2
60
0
2
Year
80
0
2
00
1
2
2030r5low
2030r5low 5%
2030r5low 95%
Economic evidence: Date at which
emissions peak critical
• PAGE also confirms that the date at which global
emissions peak is a stronger driver of avoided impacts
than is the rate at which emissions are subsequently
reduced
• A1B: equity weighted climate change impacts reach ~$32
trillion year 2000 US$ (range 29-83 trillion $$) or ~4% of
global GDP by 2100 (1-12%)
• By 2100 policy scenarios in which emissions peak in 2016
avoid ~ 20 trillion (19-19.7 across scenarios) US2000$. (The
5-95% range is 4.6-54 trillion) compared to A1B.
• i.e. 2.6-2.7% of 2100 GDP (range 0.6-7.4%GDP). Thus two
thirds of impacts may be avoided.
• By 2100 policy scenarios in which emissions peak in 2030
avoid ~15 trillion (14-16) US2000$ (3.5--45 trillion)
compared to the A1B
• i.e. 2.0-2.2% of year 2100 GDP (range 0.5-6.1). Thus half of
the impacts may be avoided.
CONCLUSION
• Date at which emissions peak is more important
than the rate of subsequent emissions reduction
in determining the avoided impacts
• Demonstrated with INDEPENDENT economic and
physically based impacts analyses
AVOID is funded by the Department of Energy and Climate Change
and the Department for Environment, Food and Rural Affairs
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