Adaptation to climate change has now become a necessity for many regions. Yet, adaptation planning at regional scales over the next few decades is challenging given the contingencies originating from a combination of different sources of climate projection uncertainty, chief among them internal variability. Here, we review the causes and consequences of internal climate variability, how it can be quantified and accounted for in uncertainty assessments, and what research questions remain most pertinent to better understand its predictive limits and consequences for science and society. This perspective argues for putting internal variability into the spotlight of climate adaptation science and intensifying collaborations between the climate modeling and application communities.

Abstract. Disentangling the effects of internal variability and anthropogenic forcing on regional climate change remains a key challenge with far-reaching implications. Due to its largely unpredictable nature on timescales longer than a decade, internal climate variability limits the accuracy of climate model projections, introduces challenges in attributing past climate changes, and complicates climate model evaluation. Here, we highlight recent advances in climate modeling and physical understanding that have led to novel insights on these key issues. In particular, we synthesize new findings from Large Ensemble simulations with Earth System Models, Observational Large Ensembles, and “dynamical adjustment” methodologies, with a focus on European climate.

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