There's a lot of physics you can do in single precision. In fact, current gen climate models are mostly in single precision, and some of the next gen models are trying to do a lot of the work in half precision (float16).
I’ll give you it’ll be algo and scale dependent. I work with climate modellers and I think they’d get more bang for their buck with optimising for GPU architectures.
I recall I was very excited at the prospect of getting my hands on a ps3 for modelling, but all my work (1) at least required double precision and it left a long bad taste in my mouth when it wasn’t to be.
