Effects of initial conditions uncertainty on regional climate variability: An analysis using a low-resolution CESM ensemble

The uncertainties surrounding the initial conditions in Earth system models can considerably influence interpretations about climate trends and variability. Here we present results from a new climate change ensemble experiment using the Community Earth System Model (CESM) to analyze the effect of internal variability on regional climate variables that are relevant for decision making. Each simulation is initialized from a unique and dynamically consistent model state sampled from a ∼10,000year fully coupled equilibrium simulation, which captures the internal unforced variability of the coupled Earth system. We find that internal variability has a sizeable contribution to the modeled ranges of temperature and precipitation. The effects increase for more localized regions. The ensemble exhibits skill in simulating key regional climate processes relevant to decision makers, such as seasonal temperature variability and extremes. The presented ensemble framework and results can provide useful resources for uncertainty quantification, integrated assessment, and climate risk management. Key Points We show CESM results sampling internal variability of the fully coupled system Ensemble exhibits skill in capturing temperature and precipitation statistics Work outlines a useful framework for UQ to guide impact analyses.