AVOID is funded by the Department of Energy and Climate Change and the Department for Environment, Food and Rural Affairs

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 7TJJason Lowe, MetOffice Hadley Centre (Reading Unit),

Department of Meteorology, University of Reading, Reading, RG6 6BB

and the AVOID WS1 Team

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

-100%

-50%

0%

50%

100%

150%

2000 2050 2100

Year

Pe

rce

nta

ge

ch

an

ge

in e

mis

sio

ns

of

CO

2 e

qu

iva

len

ts r

ela

tiv

e t

o 1

99

0

A1B Hadley

2030.R2.High

2030.R5.Low

2016.R2.High

2016.R4.Low

2016.R5.Low

Probability …

Year A1B 2016.R

(2%H, 4%L, 5%L)

2030.R

(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 analysis showed that …

Temperature implications

Jason Lowe’s work told us:

• Under A1B temperatures are likely to reach 3-4C

• 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.

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

% of impacts avoided

0

10

20

30

40

50

60

70

80

Incr

ease

dw

ater

scar

city

Flu

vial

floo

dris

k

Coa

stal

floo

dris

k

Coa

stal

man

grov

e

Dec

reas

edcr

opsu

itabi

lity

Soy

bean

prod

uctiv

ity

Coo

ling

requ

irem

ents

% o

f im

pa

cts

av

oid

ed

2016-5-L 2030-5-L

The earlier the peak in emissions, the greater the avoided impacts

Change in fluvial flood risk

0

50

100

150

200

250

300

2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

Year

% c

ha

ng

e in

flo

od

ris

k

A1b 2016-2-H 2016-4-L 2016-5-L

2030-5-L 2030-2-H

Global coastal flood plain population in the 2020s, 2050s and 2080s under the different sea-level rise scenarios

0.0%

1000.0%

2000.0%

3000.0%

4000.0%

5000.0%F

loo

din

g i

nc

rea

se

10th percentile

50th percentile

90th percentile

Net global losses of saltmarsh by the 2080s due to sea-level rise, including uncertainty

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

Nomitigation

2016.R 2030.R

Sa

ltm

ars

h l

os

s

10th percentile

50th percentile

90th percentile

Key message: Date at whichemissions 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

• The major greenhouse gases.

• Economic, non-economic and cat-

astrophic impacts.• Time horizon of 2200.• Probabilistic calculations•Eight world regions

Scope of the PAGE2002 model

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

Costs ofabatement

Costs ofadaptation

Impacts Costs

Select an abatement and adaptation policy

Global and regional

temperature

Costs ofabatement

Costs ofadaptation

Impacts Costs

Select an abatement and adaptation policy

Global and regional

temperature

Costs ofabatement

Costs ofadaptation

Impacts Costs

Select an abatement and adaptation policy

Global and regional

temperature

Costs ofabatement

Costs ofadaptation

Impacts Costs

Select an abatement and adaptation policy

Global and regional

temperature

Costs ofabatement

Costs ofadaptation

Impacts Costs

The earlier the peak in emissions, the greater the avoided impacts

Economic benefits of avoided impacts

PAGE 2002

05

101520253035

2020

2040

2060

2080

2100

Year

Eq

uit

y-w

eig

hte

d

Glo

ba

l Im

pa

cts

(y

ea

r 2

00

0)

tril

lio

n U

S$ A1B

2016r2high

2030r2high

PAGE-valued equity-weighted impacts under the AVOID policy scenarios compared to the SRES

reference scenario A1B

0.00E+00

1.00E+07

2.00E+07

3.00E+07

4.00E+07

5.00E+07

6.00E+07

7.00E+07

8.00E+07

9.00E+07

2020

2040

2060

2080

2100

Year

Eq

uit

y-w

eig

hte

d G

lob

al

Imp

ac

ts

(ye

ar

20

00

) m

illi

on

US

$

A1B

A1B 5%

A1B 95%

2016r2high

2016r2high 5%

2016r2high 95%

2016r4low

2016r4low 5%

2016r4low 95%

2016r5low

2016r5low 5%

2016r5low 95%

2030r2high

2030r2high 5%

2030r2high 95%

2030r5low

2030r5low 5%

2030r5low 95%

Economic evidence: Date at whichemissions 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