Human activities have dramatically increased forest biomass loss, increasing atmospheric carbon dioxide (CO₂) and climate change. Protecting existing forest carbon (C) stocks is a more efficient climate solution than regrowing forests, yet we lack a synthetic global overview of biomass loss drivers and intervention opportunities. In the 21^st century, human activities have directly or indirectly increased forest biomass loss around the world on spatial scales ranging from accelerated mortality of individual trees to large stand-clearing disturbances. Here, we present results from a global review of patterns and drivers of gross forest biomass loss and identify possible, effective, and broadly relevant interventions with potential to reduce biomass loss.

By far the dominant drivers are direct human actions, most notably logging, non-timber commodity production (including mining), and subsistence agriculture. Semi-natural disturbances – including storms, drought, fire, insects and pathogens, and permafrost thaw – have been increasing at alarming rates, which is attributable to anthropogenic climate change. While we lack data to accurately quantify global gross forest biomass loss, documented losses exceeded 5.1 Pg yr^-1 between 2018-2023, which is >24% of annual anthropogenic greenhouse gas emissions and >2 times estimated losses from land use change alone. While revealing the magnitude of human impact on Earth’s forests, our findings underline the vast potential for humans to reduce forest biomass loss. Reduction of greenhouse gas emissions is by far the most important intervention against the semi-natural drivers, some of which can be partially mitigated by forest management, and is essential to avoid self-reinforcing feedbacks between climate-linked forest disturbances and atmospheric CO₂ accumulation. Other effective intervention strategies include various area-based forest protection measures, which require financial and human resources for success, and reduction of commercial demand for products linked to forest loss. Implementing these at large scale will be vital both to protecting Earth’s forests and reducing the rate of atmospheric CO₂ accumulation and associated climate change.