“…While some descriptions of software design are starting to appear (e.g., Drake, 2005), detailed analysis of the design of global climate models remains a challenge because the models have undergone continued code modification for years, and, in some cases, decades. This makes a reductionist analysis of specific design decisions impossible, because each design decision is "generatively entrenched" (Lenhard and Winsberg, 2010) -that is, design features form a complex web because each has played a role in generating the others. Furthermore, each lab retains a deep but tacit knowledge base about their own models, which is readily apparent to anyone (Easterbrook and Johns, 2009), but hard to share through model intercomparison projects.…”