A world run AMOC: Simulating the forest carbon and water cycle past the tipping point of the Atlantic Meridional Overturning Circulation with a dynamic vegetation model

Adaptation measures are needed to protect forests from the impacts of climate change. To do so, forest management throughout Europe has largely shifted toward climate-smart forestry, i.e. focusing on species portfolios which are suitable under a wide range of possible future climates. These strategies primarily take into account different climate scenarios based on the Shared Socioeconomic Pathways outlined and consistently updated by the IPCC. However, evidence is mounting that the risk of the Atlantic Meridional Overturning Circulation (AMOC) collapsing in the second half of the 21st century is increasing. Such a collapse would likely entail drier and cooler conditions across Europe. This possibility is not accounted for in current climate-smart forestry approaches an complicates the task of forest management regarding suitable species choices to ensure the integrity of European forests throughout the next century. To determine optimal species portfolios for climate-smart forestry, dynamic vegetation models (DVMs) have been used due to their ability to model ecological processes under different future scenarios. However, as of yet, DVMs have not been applied to investigate the consequences of a possible AMOC collapse. Here, we use LPJ-GUESS to model the impact of an AMOC collapse on European forests from both a species composition and a carbon perspective taking into account current forest management and species selection practices. Our results suggest that an AMOC collapse in the second half of the 21st century will lead to diverging responses across Europe. Northern Europe, including the British Isles and Scandinavia is at risk of "shrubification" and subsequent decrease of forest carbon. On the other hand, coastal areas, particularly in the Mediterranean region are likely to experience an increase in forest area due to the cooler climate. Across Europe, our simulations suggest that a shift in species selection will need to occur to ensure the continued productivity and integrity of forest ecosystems. Our results underscore the need to consider the possibility of an AMOC collapse in forest management plans to ensure that the forests established today will remain viable tomorrow.