Assessing the impact of strictly protecting 30%–50% of global land on carbon dynamics in natural and agricultural ecosystems

Societal Impact Statement: Strictly protected areas for nature conservation are a key policy to benefit biodiversity and climate change mitigation since reduced deforestation and ecosystem restoration enhance carbon stocks. However, there is controversy regarding their potential societal impacts, such as competition for land and food security. Here, we investigate the implications of protecting 30% and 50% of the global ice-free land surface on the spatiotemporal dynamics of ecosystem carbon uptake and losses, agricultural land use and synergies with food production. The study provides insights into the role of protected areas on the global terrestrial carbon store, contributing to climate change mitigation and biodiversity conservation efforts. Summary: Agriculture and forestry use around half of the global ice-free land and are major drivers of biodiversity loss. For this reason, the post-2020 Global Biodiversity Framework of the Convention on Biological Diversity (CBD) targets at least 30% of protected global land by 2030. This study evaluates the impacts of different land-use change scenarios on the storage of carbon in terrestrial ecosystems and trade-offs and synergies in the global food production system by comparing a reference scenario with no additional protected area expansion targets and two scenarios with strict area-based protection targets of 30% and 50% of the ice-free land surface. A net global gain in carbon storage up to 110 PgC was projected for 2056–2060 in the protection scenarios compared to the reference scenario (equivalent to around 10 years of current global anthropogenic C emissions). However, regional disparities in carbon storage are large and include carbon losses in areas identified as having—at least on a decadal perspective—‘irrecoverable’ carbon. In the protection scenarios, cropland expansion in some regions is accompanied by intensification of production with an increase of up to 8% in the use of N fertiliser, which may lead to pollution and additional greenhouse gas emissions.