Weather and climate models are based on 64bit double precision floating-point arithmetic. Recent studies show that floats with only 32bit (single precision) or even less allow for accurate weather forecasts. However, floats might not be the best bit-wise representation of real numbers in the wider field of computational fluid dynamics. Posit numbers are a recently proposed alternative floats and although no standardised posit processor exists yet, we emulate posit arithmetic with a Julia-based emulator on a conventional CPU. A medium complexity atmosphere/ocean circulation model written in Julia is shown to be as accurate with 16bit posits as with 64bit floats. The results are promising for weather and climate models being largely based on 16bit computations with a great potential speed-up on specialised hardware in the future.