Poster: Extending the relationship between global warming and cumulative carbon emissions to...
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Extending the relationship between global warming and cumulative carbon emissions to multi-millennial timescales
Thomas L. Frölicher1 and David J. Paynter2
1Environmental Physics, ETH Zürich, Switzerland, 2Geophysical Fluid Dynamics Laboratory, Princeton, [email protected]
In a wide set of future carbon emissions scenarios,
Earth System Model (ESM) simulations and theoretical
arguments indicate an approximately linear relationship
between cumulative carbon emissions and projected
global mean temperature over the 21st century and
beyond. Any global temperature target therefore implies
a limited carbon emissions budget. On multi-millennial
Motivation(a) 1000 yr simulation of GFDL ESM2M, with prescribed atmospheric CO2 increasing at a rate
1 %/yr from 286 ppm to 745 ppm (year 99 of the simulation) when global warming is 2°C
above preindustrial levels, after which carbon emissions stop.
(b) Existing data from 12 CMIP5-ESMs and from 8 EMICs. The temperature in year 1000 for
the CMIP5-ESMs and EMICs are estimated using available 1% increasing CO2 experiments:
Methods
T1000[°C] = ECS[°C] ln((emis99[Gt C] af1000 / 2.12 Gt C ppm-1 + CO2,PI[ppm])/CO2,PI) / ln(2)
ECS: Equilibrium climate sensitivity; emis99: Cumulative carbon emissions in year 99; CO2,PI: Preindustrial CO2; af1000: Airborne fraction of anthropogenic carbon emissions
GFDL ESM2M simulates additional global warming of 0.5°C after carbon emissions are stopped at 2°C
Time (years)1000010001000
Phase I Phase II Phase III
Glo
bal m
ean
tem
pera
ture
cha
nge
(°C
)
0
1
2
3
4
5b)
Time (years)1000010001000
Com
patib
le c
umul
ativ
e ca
rbon
em
issi
ons
(Gt C
)
0
400
800
1200
1600
a)2000
Time (years)1000010000
N, R
, R-N
(W
m-2)
0
2
3
4
5
c)
Phase I Phase II Phase III
N
R - N
R
1
100
Equi
libriu
m te
mpe
ratu
re
CMIP5-ESMs also show a post-emissions increase in temperature, whereas EMICs suggest a decrease
Time (years)1000010001000
Glo
bal m
ean
tem
pera
ture
cha
nge
(°C
)
0
1
2
3
5
6
4
Phase I Phase II Phase III
a) CMIP5-ESMs
Time (years)1000010001000
Phase I Phase II Phase III
b) EMICs
Glo
bal m
ean
tem
pera
ture
cha
nge
(°C
)
0
1
2
3
5
6
4 T mean (simulated)
GFDL ESM2M
T max (estimated)
T min (estimated)
T mean + std (estimated)
T mean - std (estimated)T mean (estimated)
Individual models (simulated)
War
min
g af
ter c
arbo
n em
issi
ons
stop
page
T 1‘00
0 - T
99 (°
C)
-1.6
-0.8
0.0
1.6
2.4
0.8
0.90.80.60.4 0.5 0.7Realized warming fraction: T99 / ECS99
GFDL ESM2MCMIP5-ESMs
EMICs
r2 = 0.80
r2 = 0.24
a)
Glo
bal m
ean
tem
pera
ture
cha
nge
(°C
)
0.0
0.4
0.8
1.2
2.4
1.6
2.0T10‘000 = 2.1°C
T99 = 2.0°C
T1‘000 = 2.5°C
Cumulative carbon emissions (Gt C)16008000 400 20001200
Cumulative carbon emissions for 2°C global warming (Gt C)16008000 400 2000
GFD
LE
SM
2MC
MIP
5-E
SM
sE
MIC
s
TCRE ECRE MCREmean +std-std mean +std-std mean +std-std
b)
1200
1947
1558
1854
1388
1328
1465
1189
1590
1760
timescales when carbon emissions tape off, the coefficient relating global warming to cumulative
carbon emissions is assumed to be approximately constant or slowly decreases. This results out
of modeling studies with ESMs of Intermediate Complexity (EMICs) suggesting that global
mean temperature will either stabilize or decline post CO2 emissions. However, EMICs represent
relevant components of the Earth System, such as cloud feedbacks or ocean physics in a simpli-
fied manner and often at low resolution. Here we estimate the multi-millennial temperature re-
sponses to cumulative carbon emissions for wide a range of ESMs of different complexities. Re
f Frölicher, TL, Paynter, DJ, 2015, Extending the relationship between global warming and cumulative carbon emis-sions to multi-millennial timescales. Environ. Res. Lett, in press. Frölicher, TL, Winton, M, Sarmiento, JL, 2014, Continued global warming after CO2 emissions stoppage, Nature Climate Change, 4, 40-44.
20% lower quota on cumulative carbon emissions
0
1
2
3
4
51000 2000 3000 4000 5000 6000 7000 8000
Cumulative total anthropogenic CO2 emissions from 1870 (GtCO2)
Tem
pera
ture
ano
mal
y re
lativ
e to
186
1–18
80 (°
C)
0 500 1000 1500 2000Cumulative total anthropogenic CO2 emissions from 1870 (GtC)
2500
2050
2100
2100
2030
2050
2100
21002050
2030
2010
2000
1980
1890
1950
2050
RCP2.6 HistoricalRCP4.5RCP6.0RCP8.5
RCP range1% yr
-1 CO2
1% yr -1 CO2 range
Fig. 2: Time series of (a) compatible cumulative carbon emissions, (b) simulated (phase I and II) and estimated (phase III) global mean temperature changes and estimated equilibrium temperature changes, and (c) radiative forcing, ocean heat uptake and the difference between radiative forcing and ocean heat uptake. The radiative forcing has been calculated using the simplified expression R = 5.35 ln(CO2(t)/CO2(t=0) with CO2(t=0) = 286 ppm.
Fig. 3: Global mean temperature changes simulated (phase I) and estimated (phases II and III) by (a) 12 CMIP5 CMIP5-ESMs and (b) 8 EMICs. Fig. 4: Relationship between the realized warming fraction, T99/ECS99, in year 99 and the global temperature change over the period 99-1000 after carbon emissions tape off.
Fig. 5: (a) Relationship between global warming and cumulative carbon emissions in GFDL ESM2M. (b) Cumulative carbon emissions to remain below 2°C global warming as simulated and estimated by GFDL ESM2M, CMIP5-ESMs and EMICs for TCRE, for equilbirum climate responses to cumulative carbon emissions (ECRE), and multi-millennial climate responses to cumulative carbon emissions (MCRE).
Conclusions1. GFDL ESM2M simulates an increase in global mean surface temperature by 0.5°C after carbon
emissions are stopped at 2°C global warming, implying an increase in the coefficient relating
global warming to cumulative carbon emissions on multi-millennial timescales.
2. GFDL ESM2M also suggest a 20% lower quota on cumulative carbon emissions to achieve a
policy-driven limit on global warming.
3. CMIP5-ESMs qualitatively agree on these results. However, EMICs suggest a post-emissions
decrease in temperature, because of a smaller simulated realized warming fraction.
4. Two new metrics (ECRE and MCRE) are introduced that better characterize the long-term
temperature responses to cumulative carbon emissions.