Challenges and ways forward in ecological impact attribution

Weather extremes have multiple impacts on ecosystems, either through direct influence on plant functioning and health, or indirect and lagged impacts through disturbances such as fires, insects or pest outbreaks. Recent decades have seen an increase in high-impact extreme events, such as large-scale drought-induced mortality, crop failure, mega-fires, and widespread tree mortality events.

Understanding to which degree these events are already signs of human-driven climate change requires establishing a reference of natural climatic and ecological variability and formal attribution frameworks. Attribution of single weather extremes is challenging, but feasible through large ensembles of climate model simulations and by advanced statistical techniques. Attribution of high-impact ecological events is, however, complicated by the fact that impacts are not only driven by climate but also by internal ecological dynamics (mortality, gap dynamics, competition, succession) and human influence on the landscape and ecosystem composition (e.g., through land cover change, management, landscape fragmentation, etc.).

Here, we present a systemic framework that brings together climate risk and disturbance ecology perspectives to analyse the causal links between climate extremes, disturbances, and ecosystem dynamics. We propose an extended attribution approach that considers not only anthropogenic effects via climate change but also anthropogenic influences on ecological factors that modulate impacts. Based on this framework and on dedicated simulations by an Earth System Model, we exemplify how eco-climatic storylines can be used for robust attribution of high-impact events.