Accounting for multiple forcing factors and product substitution enforces the cooling effect of boreal forests

Abstract. There is dispute over the climate change mitigating effect of boreal forest management due to the contrasting influence it has on different vectors influencing radiative forcing (RF). For the first time, this study has combined the estimated effects of carbon sequestration in forests and wood products, the surface albedo of forests, the direct and indirect forcing of secondary organic aerosols and the avoidance of fossil emissions by product substitution, both in the current and predicted 2050 climate. The aerosol effect was comparable in magnitude to that of carbon sequestration and increased in importance in a warmer 2050 climate. Harvesting decreased the formation of climate cooling aerosols. The aerosol effect was also larger than the opposing impact of increased surface albedo due to clear cutting in conifer forests. When all above mentioned RF factors were accounted for, the RF of conifer-dominated stands was less negative than that of broadleaf-dominated stands, despite the higher carbon sequestration of the former. Considering also the cooling effect of product substitution, the differences in the RF impact of management alternatives that maintained or increased forest biomass were small. However, the outcome depended heavily on the wood use pattern and the assumed product substitution. A substantial increase in harvest with a clear increase in the share of small dimension fiber and fuel wood use led to a clear climate warming effect in the simulations.