The first fact any honest scientist should admit is that it’s simply impossible to build an accurate model of any dynamic system as complex as climate. It’s impossible to even build an accurate model of a relatively simple dynamic system like the three body problem, which is orders of magnitude simpler than the climate. It has nothing to do with model design, or computing power; we simply don’t have sufficient understanding of the underlying mathematics to do anything of the sort.
Therefore, any model that they make is very likely to be “cooked”, because they know the models will produce garbage in any case, so the temptation to force the model to produce the kind of garbage that will get them funding is going to be very strong.
Garbage in, garbage out. And of course there is the money.