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" Except where noted, adapted from Daniel et al. (1995). Calculations based on a bromine enhancement factor of a = 40 globally (see Chapter 12.D for discussion of a) and assuming phase-out of emissions as scheduled in the Copenhagen amendments to the Montreal Protocol (see Chapter 13.A for a description of these); note that WMO (1999) recommends a = 60.

h From Grossman et al. (1997).

" Except where noted, adapted from Daniel et al. (1995). Calculations based on a bromine enhancement factor of a = 40 globally (see Chapter 12.D for discussion of a) and assuming phase-out of emissions as scheduled in the Copenhagen amendments to the Montreal Protocol (see Chapter 13.A for a description of these); note that WMO (1999) recommends a = 60.

h From Grossman et al. (1997).

the direct effects of anthropogenic emissions. For example, as discussed in Chapter 12.D, atom for atom, bromine is much more effective in destroying stratospheric ozone than is chlorine. This leads to large changes in the predicted GWPs when the indirect effects of ozone destruction are taken into account. For example, the relative GWP for Halon-1301 (CF3Br) changes from net heating for the direct effect to net cooling when the indirect effect of ozone destruction is taken into account.

Figure f4.25 illustrates the estimated relative contributions to the direct heating effect and to the indirect cooling effect in 1990 and 2040, respectively (Daniel et al., 1995). The enhanced impact of the halons on cooling is particularly apparent. The net contribution of halocarbons through about 2080 is still estimated by Daniel et al. (1995) to be significant, however, in the range of O.f5-0.25 W m"2.

Such calculations also illustrate that the net effects of ozone-depleting gases on climate should change as a function of time due to changes in the chemistry. For example, Daniel et al. (1995) assume in their calculations that the stratospheric ozone loss prior to 1980 was negligible. As a result, the contribution of CFCs to radiative forcing until 1980 was estimated to be positive, in the range +0.05 to +0.10 W m-2 per decade. This rate of increase in radiative forcing should then have fallen as the indirect negative radiative forcing from ozone destruction came into play. Figure 14.26

Direct heating

Indirect cooling

Direct heating

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