Model uncertainty refers to the lack of certainty in predictions generated by models due to limitations in our understanding of the systems being modeled, the simplifications made in model structures, and the assumptions involved in parameterization. This concept is crucial for evaluating climate modeling and projections, as it highlights the challenges scientists face when attempting to predict future climate conditions accurately. Model uncertainty can stem from various sources, including incomplete data, variations in natural processes, and the inherent complexity of climate systems.