213 **Chapter 2 Changes in Atmospheric Constituents and in Radiative Forcing** 

Notes:

a The CO 2 response function used in this report is based on the revised version of the Bern Carbon cycle model used in Chapter 10 of thi s report (Bern2.5CC; Joos et

al. 2001) using a background CO 2 concentration value of 378 ppm. The decay of a pulse of CO 2 with time t is given by

Where a 0 = 0.217, a 1 = 0.259, a 2 = 0.338, a 3 = 0.186, τ 1 = 172.9 years, τ 2 = 18.51 years, and τ 3 = 1.186 years.

b The radiative effi ciency of CO 2 is calculated using the IPCC (1990) simplifi ed expression as revised in the TAR, with an updated background concentration value of 378 ppm and a perturbation of +1 ppm (see Section 2.10.2).

c The perturbation lifetime for methane is 12 years as in the TAR (see also Section 7.4). The GWP for methane includes indirect effects from enhancements of ozone

and stratospheric water vapour (see Section 2.10.3.1).

d Shine et al. (2005c), updated by the revised AGWP for CO 2 . The assumed lifetime of 1,000 years is a lower limit.

e Hurley et al. (2005)

f Robson et al. (2006)

g Young et al. (2006) i = 1 3

a 0 + 

## Σ a i • e -t/ τ i Table 2.14 (continued)

**Global Warming Potential for**

**Given Time Horizon Industrial Designation Radiative**  **or Common Name Lifetime Ef fi**  **ciency SAR ‡**  **(years) Chemical Formula (years) (W m –2**  **ppb –1)**  **(100-yr) 20-yr**  **100-yr 500-yr** 

Perfl uorinated compounds (continued)

PFC-218 C 3 F 8 2,600 0.26 7,000 6,310 8,830 12,500

PFC-318 c-C 4 F 8 3,200 0.32 8,700 7,310 10,300 14,700

PFC-3-1-10 C 4 F 10 2,600 0.33 7,000 6,330 8,860 12,500

PFC-4-1-12 C 5 F 12 4,100 0.41 6,510 9,160 13,300

PFC-5-1-14 C 6 F 14 3,200 0.49 7,400 6,600 9,300 13,300

PFC-9-1-18 C 10 F 18 >1,000 d 0.56 >5,500 >7,500 >9,500

trifl

uoromethyl SF 5 CF 3 800 0.57 13,200 17,700 21,200 sulphur pentafl uoride

Fluorinated ethers

HFE-125 CHF 2 OCF 3 136 0.44 13,800 14,900 8,490

HFE-134 CHF 2 OCHF 2 26 0.45 12,200 6,320 1,960

HFE-143a CH 3 OCF 3 4.3 0.27 2,630 756 230

HCFE-235da2 CHF 2 OCHClCF 3 2.6 0.38 1,230 350 106

HFE-245cb2 CH 3 OCF 2 CHF 2 5.1 0.32 2,440 708 215

HFE-245fa2 CHF 2 OCH 2 CF 3 4.9 0.31 2,280 659 200

HFE-254cb2 CH 3 OCF 2 CHF 2 2.6 0.28 1,260 359 109

HFE-347mcc3 CH 3 OCF 2 CF 2 CF 3 5.2 0.34 1,980 575 175

HFE-347pcf2 CHF 2 CF 2 OCH 2 CF 3 7.1 0.25 1,900 580 175

HFE-356pcc3 CH 3 OCF 2 CF 2 CHF 2 0.33 0.93 386 110 33

HFE-449sl (HFE-7100) C 4 F 9 OCH 3 3.8 0.31 1,040 297 90

HFE-569sf2 C 4 F 9 OC 2 H 5 0.77 0.3 207 59 18 (HFE-7200)

HFE-43-10pccc124 CHF 2 OCF 2 OC 2 F 4 OCHF 2 6.3 1.37 6,320 1,870 569 (H-Galden 1040x)

HFE-236ca12 CHF 2 OCF 2 OCHF 2 12.1 0.66 8,000 2,800 860 (HG-10)

HFE-338pcc13 CHF 2 OCF 2 CF 2 OCHF 2 6.2 0.87 5,100 1,500 460 (HG-01)

Perfl uoropolyethers

PFPMIE CF 3 OCF(CF 3 )CF 2 OCF 2 OCF 3 800 0.65 7,620 10,300 12,400

Hydrocarbons and other compounds – Direct Effects

Dimethylether CH 3 OCH 3 0.015 0.02 1 1 <<1

Methylene chloride CH 2 Cl 2 0.38 0.03 31 8.7 2.7

Methyl chloride CH 3 Cl 1.0 0.01 45 13 4214 **Changes in Atmospheric Constituents and in Radiative Forcing Chapter 2** 



### observed or a clear potential for future emissions has been

identi fi ed. The uncertainties of these direct GWPs are taken to be ±35% for the 5 to 95% (90%) con fi dence range.

2.10.3 Indirect GWPs

Indirect radiative effects include the direct effects of degradation products or the radiative effects of changes in concentrations of greenhouse gases caused by the presence of the emitted gas or its degradation products. Direct effects of degradation products for the greenhouse gases are not considered to be signi fi cant (WMO, 2003). The indirect effects discussed here are linked to ozone formation or destruction, enhancement of stratospheric water vapour, changes in concentrations of the OH radical with the main effect of changing the lifetime of CH 4 

### , and secondary aerosol formation. Uncertainties for the indirect GWPs are generally much higher than for the direct GWPs. The indirect GWP will in many cases depend on the location and time of the emissions. For some species (e.g., NO

x 

### ) the indirect effects can be of opposite sign, further increasing the uncertainty of the net GWP. This can be because background levels of reactive species (e.g., NO

x 

### ) can affect the chemical response nonlinearly, and/or because the lifetime or the radiative effects of short-lived secondary species formed can be regionally dependent. Thus, the usefulness of the global mean GWPs to inform policy decisions can be limited. However, they are readily calculable and give an indication of the total potential of mitigating climate change by including a certain forcing agent in climate policy. Following the approach taken by the SAR and the TAR, the CO 2 

### produced from oxidation of CH 4 

### , CO and NMVOCs of fossil origin is not included in the GWP

estimates since this carbon has been included in the national

CO 2 

### inventories. This issue may need to be reconsidered as inventory guidelines are revised.

2.10.3.1 Methane

Four indirect radiative effects of CH 4 

### emissions have been

identi fi ed (see Prather et al., 2001; Ramaswamy et al., 2001). Methane enhances its own lifetime through changes in the OH concentration: it leads to changes in tropospheric ozone, enhances stratospheric water vapour levels, and produces CO 2 

### . The GWP given in Table 2.14 includes the fi rst three of these effects. The lifetime effect is included by adopting a perturbation lifetime of 12 years (see Section 7.4). The effect of ozone production is still uncertain, and as in the TAR, it is included by enhancing the net of the direct and the lifetime effect by 25%. The estimate of RF caused by an increase in stratospheric water vapour has been increased signi fi cantly since the TAR (see Section 2.3.7). This has also been taken into account in the

GWP estimate for CH 4 

### by increasing the enhancement factor from 5% (TAR) to 15%. As a result, the 100-year GWP for CH 4 

### has increased from 23 in the TAR to 25. 2.10.3.2 Carbon Monoxide

The indirect effects of CO occur through reduced OH levels (leading to enhanced concentrations of CH 4 

### ) and enhancement of ozone. The TAR gave a range of 1.0 to 3.0 for the 100-year GWP. Since the TAR, Collins et al. (2002) and Berntsen et al. (2005) have calculated GWPs for CO emissions that range between 1.6 and 2.0, depending on the location of the emissions. Berntsen et al. (2005) found that emissions of CO from Asia had a 25% higher GWP compared to European emissions. Averaging over the TAR values and the new estimates give a mean of 1.9 for the 100-year GWP for CO.

2.10.3.3 Non-methane Volatile Organic Compounds

Collins et al. (2002) calculated indirect GWPs for 10 NMVOCs with a global three-dimensional Lagrangian chemistry-transport model. Impacts on tropospheric ozone,

CH 4 

### (through changes in OH) and CO 2 

### have been considered, using either an ‘anthropogenic’ emission distribution or a ‘natural’ emission distribution depending on the main sources for each gas. The indirect GWP values are given in Table 2.15. Weighting these GWPs by the emissions of the respective compounds gives a weighted average 100-year GWP of 3.4. Due to their short lifetimes and the nonlinear chemistry involved in ozone and OH chemistry, there are signi fi cant uncertainties in the calculated GWP values. Collins et al. (2002) estimated an uncertainty range of –50% to +100%.

2.10.3.4 Nitrogen Oxides

The short lifetime and complex nonlinear chemistry, which cause two opposing indirect effects through ozone enhancements

and CH 4 

### reductions, make calculations of GWP for NO

x 

### emissions very uncertain (Shine et al., 2005a). In addition, the effect of nitrate aerosol formation (see Section 2.4.4.5), which has not yet been included in model studies calculating GWPs

for NO

x 

### , can be signi fi cant. Due to the nonlinear chemistry, the

net RF of NO

x 

### emissions will depend strongly on the location of emission and, with a strict de fi nition of a pulse emission for the GWP, also on timing (daily, seasonal) of the emissions (Fuglestvedt et al., 1999; Derwent et al., 2001; Wild et al., 2001;

Stevenson et al., 2004; Berntsen et al., 2005, 2006). Due to the lack of agreement even on the sign of the global mean GWP for

NO

x 

### among the different studies and the omission of the nitrate aerosol effect, a central estimate for the 100-year GWP for NO

x 

### is not presented.

2.10.3.5 Halocarbons

Chlorine- and bromine-containing halocarbons lead to ozone depletion when the halocarbon molecules are broken down in the stratosphere and chlorine or bromine atoms are released. Indirect GWPs for ozone-depleting halocarbons are estimated in Velders et al. (2005; their Table 2.7). These are based on