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The concept of Global Warming Potentials (GWPs) has been extensively used inpolicy consideration as a relative index for comparing the climate impact ofan emitted greenhouse gas (GHG), relative to carbon dioxide with equal massemissions. Ozone depletion due to emission of chlorinated or brominatedhalocarbons leads to cooling of the climate system in the opposite directionto the direct warming contribution by halocarbons as GHGs. This cooling is akey indirect effect of the halocarbons on climatic radiative forcing, whichis accounted for by indirect GWPs. With respect to climate, it is criticalto understand net influences considering direct warming and indirect coolingeffects especially for Halons due to the greater ozone-depleting efficiencyof bromine over chlorine. Until now, the indirect GWPs have been calculatedusing a parameterized approach based on the concept of Equivalent EffectiveStratospheric Chlorine (EESC) and the observed ozone depletion over the lastfew decades. As a step towards obtaining indirect GWPs through a more robustapproach, we use atmospheric models to explicitly calculate the indirectGWPs of Halon-1211 and Halon-1301 for a 100-year time horizon.State-of-the-art global chemistry-transport models (CTMs) were used as thecomputational tools to derive more realistic ozone depletion changes causedby an added pulse emission of the two major Halons at the surface. Theradiative forcings on climate from the ozone changes have been calculatedfor indirect GWPs using an atmospheric radiative transfer model (RTM). Thesimulated temporal variations of global average total column Halons after apulse perturbation follow an exponential decay with an e-folding time whichis consistent with the expected chemical lifetimes of the Halons. Ourcalculated indirect GWPs for the two Halons are much smaller than those frompast studies but are within a single standard deviation of WMO (2007) valuesand the direct GWP values derived agree with the published values. Ourmodel-based assessment of the Halon indirect GWPs thus confirms thesignificant importance of indirect effects on climate

Explicit calculation of indirect global warming potentials for halons using atmospheric models