Assessing cumulative risks – an expert evaluation of ecosystem services

Ocean environments and their services face a plethora of stressors of human origin, where knowledge of effects and their probability is limited, requiring expert opinion for risk assessment. Individual stressors or drivers of change may pose small risks, but the cumulative risks may be considerable. In this study, using a survey related to the Barents Sea, we apply two approaches for assessing cumulative risk to ecosystem services: one stated directly by the experts, and the other estimated by aggregating expert-based individual risks using a multiplicative model. Comparing the results reveals that the stated cumulative risk is significantly smaller than the aggregate cumulative risk. This disparity arises because the experts appear to be averaging over all individual risks when stating cumulative risk. When identifying individual risks, they already seem to consider the synergies between drivers, potentially impacting aggregate cumulative risk. These aspects raise questions about how cumulative risk assessment is carried out and point to the need to clearly express cumulative risks as well as individual risks in surveys. The study also demonstrates that there may be interdependencies or correlations among risks, which can significantly impact the aggregate risk outcome, underlining the importance of considering interdependencies when assessing risk.