Beyond carbon, from Arctic forest migration to climate mitigation: can biogeochemical effects challenge albedo-driven warming?

Rising global temperatures are expected to drive a northward expansion of boreal forests into Arctic regions, triggering multiple and interacting climate feedbacks. This land cover change is also relevant as a parallel to mitigation strategies such as afforestation, which are often evaluated solely for their carbon benefits, while other biogeophysical and biogeochemical effects may substantially offset the intended carbon uptake. Reduced surface albedo from forests replacing snow-covered, treeless areas is widely recognised as a strong warming mechanism. Chemical emissions, specifically biogenic volatile organic compounds (BVOCs), in these regions may also play a substantial role, potentially counteracting albedo-driven warming. In this study, we aim to provide new insights into the climate impacts of Arctic land cover change by assessing both biogeophysical and biogeochemical pathways beyond carbon uptake.BVOCs influence climate through multiple, partly opposing pathways. Their oxidation products contribute directly to secondary organic aerosol formation and modify indirectly cloud optical properties, potentially leading to a cooling effect. At the same time, BVOCs affect atmospheric chemistry by altering the concentrations and lifetimes of key climate forcers such as ozone and methane, which can introduce a positive radiative forcing. The combined effect of these processes, and their relative importance compared to albedo changes, remains uncertain.Here, we use the Norwegian Earth System Model version 2.3 (NorESM2.3), including a newly implemented comprehensive atmospheric chemistry scheme, to investigate the radiative impacts of projected boreal forest expansion. We perform targeted simulations under present-day and warmer climate scenarios, allowing us to isolate the contributions from surface albedo changes, BVOC-driven direct aerosol effects, cloud interactions, and chemistry-related impacts on ozone and methane.By comparing these pathways within a single modelling framework, this work evaluates whether BVOC-related processes can significantly offset albedo-driven warming and how their relative importance evolves under climate warming. The results provide a comprehensive understanding of how land use and land cover changes influence the Arctic climate via interacting biogeophysical and biogeochemical mechanisms.