Editing IPCC:AR6/WGI/Chapter-10 (section)

==== 10.3.4.1 Propagation of Uncertainties ====

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Modelling chains for generating regional climate information range from the definition of forcing scenarios to the global modelling, and potentially to dynamical or statistical downscaling and bias adjustment ( [[#10.3.1|Section 10.3.1]] ). The propagation and potential accumulation of uncertainties along the chain has been termed the cascade of uncertainty ( [[#Wilby--2010|Wilby and Dessai, 2010]] ). Even within one model, like a global model, uncertainty propagates across scales. From a process point of view, these uncertainties are related to forcings and global climate sensitivity, and errors in the representation of the large-scale circulation ( [[#10.3.3.3|Section 10.3.3.3]] ; [[#McNeall--2016|McNeall et al., 2016]] ) and regional processes ( [[#10.3.3.4|Section 10.3.3.4]] ), feedbacks ( [[#10.3.3.5|Section 10.3.3.5]] ) and drivers ( [[#10.3.3.6|Section 10.3.3.6]] ). From a modelling point of view, these uncertainties are related to the choice of dynamical and statistical models ( [[#10.3.1|Section 10.3.1]] ) and experimental design ( [[#10.3.2|Section 10.3.2]] ). The overall uncertainty can be statistically decomposed into the individual sources ( [[#Evin--2019|Evin et al., 2019]] ; [[#Christensen--2020|Christensen and Kjellström, 2020]] ), although there might be non-linear dependencies between them.

Uncertainty propagation often increases the spread in regional climate projections when comparing global model and downscaled results, which has been used as an argument against top-down approaches to climate information ( [[#Prudhomme--2010|Prudhomme et al., 2010]] ). Increased spread in the modelling chain may also arise from a more comprehensive representation of previously unknown or underrepresented uncertainties ( [[#Maraun--2018b|Maraun and Widmann, 2018b]] ). The increased spread in this case goes together with a better representation of processes and thus an increased model fitness-for-purpose ( [[#10.3.3.9|Section 10.3.3.9]] ).

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