1. Radiative Forcing and Global Warming Potentials due to CH4 and N2O
Workshop on common metrics to calculate the CO2 equivalence of anthropogenic greenhouse gas emissions by sources and removals by sinks
Radiative Forcing and Global Warming Potentials due to CH4 and N2O
Hua Zhang Ruoyu Zhang
National Climate Center
China Meteorological Administration
April 3-4, 2012
Bonn, Germany

2. Outline Backgrounds Data & Methods Radiative forcings GWPs & GTPs1
Backgrounds 2
Data & Methods 2
Radiative forcings 3
GWPs & GTPs 4
Discussion 5

3. Concentrations of main GHGs before 2005
Backgrounds
Concentrations of main GHGs before 2005
CH4 (pptv)
C02 (ppmv)
N20 (pptv)
year（before 2005）

4. Concentrations of main GHGs under SRES scenarios

5. Backgrounds
气候变化的一种机制
通过辐射传输过程

6. Radiative forcing (RF)
Methods
Radiative forcing (RF)

7. Time-decaying functions
Methods
Radiative efficiency
Time-decaying functions
GWP
RF of GHG x
RF of CO2
1 GWP is related to emission process of GHG;
2 GWP can convert any kind of GHG equivalently to
CO2 emission, which makes the comparison easily among different gases;
3 GWP denotes the cumulative climate effect of the
GHG during a period of time.

8. Surface temperature changes
Methods
GTP
T changes with time
Surface temperature changes
T arrives at balance not varying
1 GTP refers to emission process of GHGs too ;
2 GTP can convert any kind of GHGs equivalently to
CO2 emission too;
GTP denotes the effect of GHG on the temperature
changes of the earth-atmosphere system.

9. Radiative Transfer Model
Model & Data
Radiative Transfer Model
(Zhang et al., 2003; 2006a,b)
998-band longwave radiative transfer
scheme (high resolution)
10~49000cm-1 (0.2~1000µm) is divided into 998
bands
longwave region 10~2500cm-1(4~1000µm）
is 498 bands with intervals of 5cm-1

10. Gas molecular spectrum data Atmosphere profiles data
Model & Data
辐射传输模式
Gas molecular spectrum data
辐射传输模式
辐射传输模式
辐射传输模式
辐射传输模式
HITRAN2004
Atmosphere profiles data
6 kinds of typical model atmosphere :
TRO、MLS、MLW、SAS、SAW、USS
Clouds
ISCCP D2 products

11. Criterion: to judge whether the system reaches to balance
Iteration to calculate ARF
Temperature profile T0(L)
kn=0
Radiative Transfer Model
(Zhang et al.，2006)
Radiative Transfer Model
(Zhang et al.，2006)
Heating rate for zero concentration: htr0(L)
Heating rate for 0.1 ppbv concentration: htr1(L)
iterationkn=kn+1
Criterion: to judge whether the system reaches to balance
kn=0
Heating rate
Htrdif（L）=htr1(L) - htr0(L)
Instantaneous RF
htrdif（L）<ξ N
Tnew（L）=Told（L）+htrdif（L）×△t
L：from Tropopause to TOA Y
Adjusted RF

12. Doubled CO2 , H2O increase by 20%
Model tests
Doubled CO2
Doubled CO2 , H2O increase by 20%
Model layer
998-band
AOGCMs
LBL
TOM
3.03
2.45
2.8
3.26
3.75
3.78
200 hPa
5.6
5.07
5.48
4.13
4.45
4.57
Surface
1.7
1.12
1.64
11.14
11.95
11.52
（1）CO2 concentration is doubled from 287 ppmv to 574 ppmv；
（2）With doubled CO2 concentration (574 ppmv), H2O content is increased by 20% of its concentration of 1860 year

13. Results Radiative efficiency Gas Clear sky Cloudy sky IPCC 2007 IRE
ARE
ARE after lifetime-
adjustment
CO2
1.99E-5
1.88E-5
1.64E-5
1.57E-5, %
1.4E-5
CH4
5.13E-4
5.06E-4
4.14E-4
3.73E-4, +0.8%
3.7E-4
N2O
3.87E-3
3.79E-3
3.13E-3
2.98E-3, -1.4%
3.03E-3
* unit：W·m-2·ppbv-1
** Lifetime : CO2 : 120a ; CH4 : 12a ; N2O : 114a

14. Radiative forcings (ARF)
Results
Radiative forcings (ARF)
Gas
2005
2010
IPCC
2007
before
adjustment
After
Before
CO2
1.89
1.81
2.04
1.95
1.66±0.17
CH4
0.581
0.523
0.583
0.525
0.48±0.05
N2O
0.185
0.177
0.187
0.179
0.16±0.02
* unit：W·m-2
** Lifetime : CO2 : 120a ; CH4 : 12a ; N2O : 114a

15. Results IPCC : 1.5~4.5K Climate sensitivity parameter : λ
Its typical value is chosen as 0.5K·(W·m-2)-1
Original concentration of CO2 : ppmv
Then:
IPCC : 1.5~4.5K
Concentration
ARF
/ W m-2
Temperature
Changes / K
CO2×1.5
2.8
1.4
CO2×2.0
4.8
2.4
CO2×2.5
6.4
3.2
CO2×3.0
7.8
3.9
CO2×3.5
9.0
4.5
CO2×4.0
9.8
4.9

16. Results ARF fitting formula C : CO2 concentration;
C0 : background CO2 concentration,
C0 = ppmv;
fitting parameters : α=6.2554, β=5.2783×10-2

17. Results 6种大气廓线下 ARF fitting formula
CH4 background concentration M0=1797ppbv;
0≤M0,N0≤10000 ppbv ;
fitting parameters : α= , β=1.439×10-4,
γ=-1.133×10-3, δ=1.221×10-7
N2O background concentration N0=321.8ppbv
0≤M0,N0≤10000 ppbv;
fitting parameters : α= , β=0.0011
γ= ×10-4, δ= ×10-9

18. Results Test of fitting * Shi et al., absolute error≤0.05 W m-2
Test issue
Model results
/ W m-2
Formula results
Absolute
error
CO2×2 + CH4×2 + N2O×2
6.07
6.05
0.02
CO2×2 + CH4×1 + N2O×1
4.70
4.76
0.06
CO2×2 + CH4×2 + N2O×1
5.36
5.30
CO2×1 + CH4×2 + N2O×2
1.32
1.29
0.03
* Shi et al., absolute error≤0.05 W m-2

19. Results before atmospheric lifetime adjustment
Gas
GWP
IPCC 2007
GTPP
GTPS
20 / 100 / 500
CH4
50 / 17 / 5.3
72 / 25 / 7.6
41 / 0.26 / ~0
56 / 19 / 5.4
N2O
258 / / 137
289 / 298 / 153
268 / 233 / 11
250 / 269 / 139
after atmospheric lifetime adjustment 气体
GWP
IPCC 2007
GTPP
GTPS
20 / 100 / 500
CH4
47 / 16 / 5
72 / 25 / 7.6
39 / 0.24 / ~0
53 / 18 / 5
N2O
257 / 266 / 136
289 / 298 / 153
268 / 233 / 11
250 / 268 / 138

20. Analytical calculation
Results
For comparison :
Shine（2005）results
Gas
Analytical calculation
EBM
GTPP
GTPS
20 / 100 / 500
CH4
52 / 0.35 / 0
69 / 24 / 7
46 / 5 / 0.8
66 / 25 / 8
N2O
290 / 270 / 13
260 / 290 / 160
290 / 270 / 35
270 / 290 / 160

21. After the lifetime-adjustment Atmosphere lifetime /a
Gas
Atmosphere lifetime /a
AGWP / 10-14·W·m-2·kg-1
20 / 100 / 500
CO2
120
2.72 / 9.57 / 31.5
CH4 12
127.7 / / 157.4
N2O
114
700.3 / 2542 / 4298
HFC-32
4.9
6613 / 6727 / 6727
HFC-125 29
19971 / / 40083
HFC-134 10
12962 / / 14991
HFC-134a 14
12320 / / 16204
HFC-143a 52
24107 / / 75499
HFC-152a
1.4
1573 / 1573 / 1573
C2F6
10000
28168 / / 68757
CF4
50000
12527 / /
SF6
3200
52193 / /

22. Results Before atmospheric lifetime adjustment
Gas
AGTPP / 10-16·K·kg-1
AGTPS / 10-14·K·kg-1
20 / 100 / 500
CH4
372 / 1.62 / ~0
73.8 / / 139.7
N2O
2419 / 1465 / 43.9
328.9 / 1972 / 3593
CO2
9.04 / 6.28 / 3.89
1.31 / 7.34 / 25.9
After atmospheric lifetime adjustment
Gas
AGTPP / 10-16·K·kg-1
AGTPS / 10-14·K·kg-1
20 / 100 / 500
CH4
336 / 1.46 / ~0
66.5 / / 125.9
N2O
2312 / 1401 / 41.9
314 / 1884 / 3434
CO2
8.64 / 6.01 / 3.72
1.26 / 7.02 / 24.8

23. Results Gas AGTPP / 10-16·K·kg-1 AGTPS / 10-14·K·kg-1 20 / 100 / 500
HFC-32
16834 / 10.2 / ~0
5209 / 7118 / 7119
HFC-125
80622 / 7321 / 0.008
12550 / / 42393
HFC-134
35691 / 59.9 / ~0
8093 / / 14021
HFC-134a
44445 / 361 / ~0
8322 / / 17160
HFC-143a
46423 / / 5.9
13945 / / 75986
HFC-152a
2755 / 1.5 / ~0
1376 / 1669 / 1669
C2F6
/ /
16213 / /
CF4
51547 / / 60241
6683 / /
SF6
/ /
30283 / /

24. AGTPP of CH4 & N2O
AGTPS of CH4 & N2O

25. AGTPP of CO2 AGTPS of CO2 Temperature changes (10-16K)
Time (a)
AGTPS of CO2
Time (a)

26. Discussion
The lifetimes of CH4 are relatively short-lived GHGs; GWP greatly over-estimates the effects of their pulse emission on climate changes.
GTPp is an optimal metric for assessing the long-term effects of CH4 emissions on global climate change, by considering practical emissions of these gases.

27. Climate sensitivity parameter λ can affect AGWP and AGTP greatly, this should be considered as a large uncertainty in estimating process.
AGWPs and AGTPs of long-lived GHGs are sensitive to time horizon; while AGTPp of short-lived GHGs is sensitive to time horizon greatly.
Clouds is another large factor of uncertainties in estimating GWP or GTP
and should be clarified in IPCC AR5 report.

28. Thanks！ 28