[cogitator]

And they are now?

Yes. Not for accurate predictions, mind you*, but for actual evaluation of current climate influences and trends, they can (and are) used to evaluate Earth's climate

* partly due to unresolvable uncertainty regarding societal, technological, and economic changes in the future

[palmer]

Here's one problem with your models: the MCS that came through No. VA this morning affected our climate temporarily affected our climate by bringing down colder air from aloft and leaving behind lingering clouds. None of that is in current models (resolution of about 200 miles). It certainly matters to accurately model the effects of water vapor in both condensed and uncondensed forms. Without that, you fail to model the consequences of forcing (man-made increases in CO2 causing slight warming causing increases in water vapor). There is no way to accurately depict the extra water vapor without clouds and precipitation that are often localized phenomena (a small local vortex in our case).

Fortunately, computation power is increasing and adequate models should arrive in the next decade or so.