Tree2Globe · Global reanalysis for a forest carbon sink in flux

Three trillion trees lie behind a carbon sink that has taken up about 30% of humanity’s carbon emissions over recent decades. Yet whether we can continue to rely on this huge natural subsidy is highly uncertain. The sink emerges from systematic perturbations in the dynamics of growth, death and establishment of individual trees. Taken together across the forest, these lead to the net uptake or release of carbon. Both theory and recent observations point towards profound changes in these dynamics of the world’s forests being underway, potentially causing the sink to saturate and decline. But our ability to accurately assess and quantify such on-going changes worldwide is severely limited. The reasons for this are twofold: a lack of standardised measurements of the sink and the dynamics that cause it across the world, and the difficulty of modelling the dynamics of trillions of trees. Tree2Globe solves both of these limitations, using a novel model-data assimilation approach to consistently integrate the dynamics of millions of observations of individual trees collected under disparate protocols worldwide and link together this information in space and time based on physically-consistent principles. The resulting global forest reanalysis system will (a) provide a step-change in capability to make accurate and timely assessment of the rates of tree growth, death and establishment globally and (b) quantify how these combine with the legacies of past land-use and disturbance to explain the size, location and trajectory of the global carbon sink in trees over the period 1990-2027. This will enable us to make a definitive assessment of whether hypothesised changes in forest dynamics and the resulting carbon sink are coming to pass. This unique insight into how the world’s forests and their contribution to climate change mitigation are changing will provide key information to help guide the world to meet its net zero emissions policy commitments.