Abstract: The basic problem faced in geophysical fluid dynamics is that a mathematical description based only on fundamental physical principles, the so-called the ``Primitive Equations'', is often prohibitively expensive computationally, and hard to study analytically. In this talk I will discuss the main obstacles in proving the global regularity for the three-dimensional Navier-Stokes equations and their geophysical counterparts. However, taking advantage of certain geophysical balances and situations, such as geostrophic balance and the shallowness of the ocean and atmosphere, geophysicists derive more simplified and manageable models which are easier to study analytically. In particular, I will present the global well-posedness for the three-dimensional B\'enard convection problem in porous media, and the global regularity for a three-dimensional viscous planetary geostrophic models. Even though the primitive equations look as if they are more difficult to study analytically than the three-dimensional Navier-Stokes equations I will show, on the one hand, that the viscous primitive equations have a unique global (in time) regular solution for all initial data. On the other hand, I will show that in the non-viscous (inviscid) case there is a one-parameter family of initial data for which the corresponding smooth solutions develop finite-time singularities (blowup). This is a joint work with Chongsheng Cao, Slim Ibrahim and Kenji Nakanishi.