A recursively changing noise seed based heightmap would be easy. Much better would be, getting yourself a NASA Pressure and temperature map(they also have air moisture, solar input etc, maps) converting it into several heightmaps and do computations on those as a start. That way you can also better see what you should be getting.
In total however for a real simulation you would have to account for Coriolis force(earth gyro spin), Day and night cycles, Temperature, Pressure, Ocean and land heat transfer, air moisture and solar insolation. In other words, quite a bit.
