Radiative Forcing and Global Warming Potentials due to CH 4 and N 2 O Hua Zhang Ruoyu Zhang National Climate Center China Meteorological Administration April 3-4, 2012 Bonn, Germany Workshop on common metrics to calculate the CO2 equivalence of anthropogenic greenhouse gas emissions by sources and removals by sinks

Backgrounds Data & Methods Radiative forcings GWPs & GTPs Discussion

year （ before 2005 ） C0 2 (ppmv) CH 4 (pptv) N 2 0 (pptv) Concentrations of main GHGs before 2005

Concentrations of main GHGs under SRES scenarios

气候变化的一种机制 通过辐射传输过程

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

1 GTP refers to emission process of GHGs too ; 2 GTP can convert any kind of GHGs equivalently to CO2 emission too; 3GTP denotes the effect of GHG on the temperature changes of the earth-atmosphere system. T changes with time Surface temperature changes T arrives at balance not varying

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 Radiative Transfer Model (Zhang et al., 2003; 2006a,b)

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

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

（ 1 ） CO 2 concentration is doubled from 287 ppmv to 574 ppmv ； （ 2 ） With doubled CO 2 concentration (574 ppmv), H 2 O content is increased by 20% of its concentration of 1860 year Doubled CO 2 Doubled CO 2, H 2 O increase by 20% Model layer 998- band AOGCMsLBL998-bandAOGCMsLBL TOM hPa Surface

Gas Clear skyCloudy sky IPCC 2007 IREARE ARE after lifetime- adjustment ARE CO E-51.88E-51.64E-51.57E-5, +11.9%1.4E-5 CH E-45.06E-44.14E-43.73E-4, +0.8%3.7E-4 N2ON2O3.87E-33.79E-33.13E-32.98E-3, -1.4%3.03E-3 * unit ： W·m -2 ·ppbv -1 ** Lifetime : CO 2 : 120a ; CH 4 : 12a ; N 2 O : 114a Radiative efficiency

Gas IPCC 2007 before adjustment After adjustment Before adjustment After adjustment CO ±0.17 CH ±0.05 N2ON2O ±0.02 * unit ： W·m -2 ** Lifetime : CO 2 : 120a ; CH 4 : 12a ; N 2 O : 114a Radiative forcings (ARF)

Climate sensitivity parameter : λ Its typical value is chosen as 0.5K·(W·m -2 ) -1 Original concentration of CO 2 : ppmv Then: Concentration ARF / W m -2 Temperature Changes / K CO 2 × CO 2 × CO 2 × CO 2 × CO 2 × CO 2 × IPCC : 1.5~4.5K

C : CO 2 concentration; C 0 : background CO 2 concentration, C 0 = ppmv; fitting parameters : α=6.2554, β=5.2783×10 -2 ARF fitting formula

6 种大气廓线下 CH 4 background concentration M 0 =1797ppbv; 0≤M 0,N 0 ≤10000 ppbv ; fitting parameters : α= , β=1.439×10 -4, γ=-1.133×10 -3, δ=1.221×10 -7 N 2 O background concentration N 0 =321.8ppbv 0≤M 0,N 0 ≤10000 ppbv; fitting parameters : α= , β= γ= ×10 -4, δ= ×10 -9 ARF fitting formula

Test of fitting Test issue Model results / W m -2 Formula results / W m -2 Absolute error / W m -2 CO 2 ×2 + CH 4 ×2 + N 2 O× CO 2 ×2 + CH 4 ×1 + N 2 O× CO 2 ×2 + CH 4 ×2 + N 2 O× CO 2 ×1 + CH 4 ×2 + N 2 O× * Shi et al., absolute error≤0.05 W m -2

Gas GWP IPCC 2007 GTP P GTP S 20 / 100 / 500 CH 4 50 / 17 / / 25 / / 0.26 / ~056 / 19 / 5.4 N2ON2O258 / / / 298 / / 233 / / 269 / 139 after atmospheric lifetime adjustment before atmospheric lifetime adjustment 气体 GWP IPCC 2007 GTP P GTP S 20 / 100 / 500 CH 4 47 / 16 / 572 / 25 / / 0.24 / ~053 / 18 / 5 N2ON2O257 / 266 / / 298 / / 233 / / 268 / 138

Gas Analytical calculationEBM GTP P GTP S GTP P GTP S 20 / 100 / 500 CH 4 52 / 0.35 / 069 / 24 / 746 / 5 / / 25 / 8 N2ON2O290 / 270 / / 290 / / 270 / / 290 / 160 Shine （ 2005 ） results For comparison :

Gas Atmosphere lifetime /a AGWP / ·W·m -2 ·kg / 100 / 500 CO / 9.57 / 31.5 CH / / N2ON2O / 2542 / 4298 HFC / 6727 / 6727 HFC / / HFC / / HFC-134a / / HFC-143a / / HFC-152a / 1573 / 1573 C2F6C2F / / CF / / SF / / After the lifetime-adjustment

Gas AGTP P / ·K·kg -1 AGTP S / ·K·kg / 100 / 500 CH / 1.62 / ~073.8 / / N2ON2O2419 / 1465 / / 1972 / 3593 CO / 6.28 / / 7.34 / 25.9 After atmospheric lifetime adjustment Before atmospheric lifetime adjustment Gas AGTP P / ·K·kg -1 AGTP S / ·K·kg / 100 / 500 CH / 1.46 / ~066.5 / / N2ON2O2312 / 1401 / / 1884 / 3434 CO / 6.01 / / 7.02 / 24.8

Gas AGTP P / ·K·kg -1 AGTP S / ·K·kg / 100 / 500 HFC / 10.2 / ~05209 / 7118 / 7119 HFC / 7321 / / / HFC / 59.9 / ~08093 / / HFC-134a / 361 / ~08322 / / HFC-143a / / / / HFC-152a 2755 / 1.5 / ~01376 / 1669 / 1669 C2F6C2F / / / / CF / / / / SF / / / /

AGTP S of CH 4 & N 2 O AGTP P of CH 4 & N 2 O

AGTP S of CO 2 AGTP P of CO 2 Temperature changes ( K) Temperature changes ( K) Time (a)

The lifetimes of CH 4 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 CH 4 emissions on global climate change, by considering practical emissions of these gases.

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.

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