Mitigation of short-lived heating components may lead to unwanted long-term consequences

A mitigation strategy for reducing emissions of short-lived heating components such as black carbon (BC) aerosols and ozone precursors to limit global warming has frequently been suggested (Bond, 2007; Grieshop et al., 2009; Hansen et al., 2000; Jacobson, 2002; Molina et al., 2009; Nature Editorial, 2009). BC emissions influence the radiative balance in several ways through direct and semi-direct aerosol effects, as well as by impacting the surface albedo (Forster et al., 2007), and their net effect is likely a warming that enhances the total man-made warming. However, the role that BC or other short-lived heating components may play in future mitigation strategies must be formulated with caution to avoid unforeseen and unwanted consequences. A near-term mitigation of short-lived heating components could lead to a delayed action on CO2 and other long-lived greenhouse gases and thus an increased long-term warming. A key element is whether policies are designed as a consequence of predicted warming or observed warming. Without a clear strategy, early BC or ozone reductions may even lead to an unexpectedly larger temperature change.