A global map of Earth system interactions

Abstract. The intricate interplay of the biophysical processes of the Earth system provides the basis for Earth resilience and human well-being. With local anthropogenic pressures increasing in most regions, there has been a growing need for a systemic understanding of this interplay on a sub-global scale. However, due to inconsistency in the temporal and spatial scales in the corresponding studies, a holistic assessment of the environmental impact of local human activities remains challenging. We take a step in the direction of a uniform framework for estimating, exploring, and communicating the spatially resolved global pattern of crucial Earth system interactions. We focus on the processes of change in carbon dioxide concentration, natural vegetation cover, and surface water runoff, representing the major components of the Earth system of climate, land, and the global water cycle, respectively. In a first step, we quantify local interactions based on historical simulations of the dynamical global vegetation model LPJmL. In a second step, we approach the question of a global partition into coherent interaction zones, illustrating the risk of information loss that comes with established spatial aggregations. Following a top-down approach first, we map the global interaction pattern on common natural partitions of the Earth. Cluster validity indices reveal a close alignment between the effect of land use change on climate and biogeographic classification by biome. In contrast, the effects of land use change and climate change on surface water runoff are best captured by the Köppen-Geiger climate zones. Following a bottom-up approach, we use multivariate spatially constrained clustering to derive integrative global partitions and analyze the interaction profile of the resulting clusters. Showing particularly strong combined effects, we identify several patches of tropical rainforest on the Indomalayan islands, as well as large areas of warm grasslands in Australia, as high-impact clusters with respect to secondary effects of human pressures on land and climate. Our study emphasizes the local nature of the interplay of Earth system interactions as well as both the risks and potential that spatial aggregation entails.