Complex sentence: Secondly, the time and spatial scales for forcings between the Earth's surface and atmosphere occur on scales much less than the scales at which GCMs are run, and need to be parameterized as a result (cite DL Hartmann's book, Chapter 10).
Split into simpler sentences: Secondly, the time and spatial scales for forcings between the Earth's surface and atmosphere occur on scales much less than the scales at which GCMs are run. So, many of these forcings need to be parameterized as a result.need to be parameterized as a result (cite DL Hartmann's book, Chapter 10).