I hate to break it to you but all programming is highly specialized. Climatology is in no way special in this regard.
Neither do programmers have to understand the abstract model of the program to write it or evaluate it. The vast majority of professional programmers do not understand the abstract model of the code they create. You do not have to be a high-level accountant to write corporate accounting software and you don't have to be a doctor to write medical software. Most programmers spend most of their time implementing models created by non-programmers from fields of which the programmers have no detailed knowledge.
Does that mean that programmers can't spot crappy code just because they don't understand the details of the model? No, it does not. Most software errors don't arise from the model but from sloppy practices in the management of the software project itself. An experienced programmer doesn't even have to know the language of project to see that it's creation and maintenance was incompetently handled.
You don't have to be a climatologist to know that the CRU software was utter crap that would produce sound outputs only by divine intervention. For any experienced programmer, it was immediately obvious that it was a great reeking gob of amateur coding with no structure, no plan and no standards. In my experience, most scientific software is like the CRU software. It evolves in an ad hoc manner over many years with no governing organizational structure.
Commercial software developers have created a wide range of tools and procedures to manage large, vital projects. In the main, scientist use none of these tools and most of them appear unaware they even exist much less why and when they are needed. As a result most scientific software project management is completely amateurish. If most scientific software were written for commercial applications, the developers would be sued or imprisoned for fraud.
Scientist tend to be arrogant and dismissive of the work of others especially those who work in the commercial sector. You believe that because you understand climatology that you therefore understand all the tools you are using. Well you don't. You think that because no one can understand your abstract model that therefore they cannot find significant errors in your code. Well, they can. You think we should reengineer our entire civilization based on your unquestioned and unexamined computerized ivory tower auguries.
Well, we won't.
Your just going to have to suck it up and withstand the at least the same scrutiny we give important commercial software.