The model assumes that ice sheets are mostly split up by basal sheer stress, and it is not necessary to consider the other forces. It also assumes that the basal shear stress and the gravitational driving stress of the grounded ice balance one another out. The method is computationally inexpensive. Shallow Shelf Approximation Shallow Shelf Approximation is another method to model ice flow, in particular a membrane-type flow of floating ice, or of sliding grounded ice over a base. Also known as a membrane model, they are similar to free-film models in fluid dynamics. As opposed to Shallow Ice Approximation, Shallow Shelf Approximation models ice flow when longitudinal forces are strong; sliding and vertical forces. SSA can also be considered a 'zero-order' model. Full Stokes Equations It is considered advantageous to model ice using Navier-Stokes equations as ice is a viscous fluid and these capture all forces exerted on the ice. As these equations are computationally expensive, it is important to include many approximations to reduce running time. Because of their computational expense, they are not easily used at a large scale and can be used in specific sections or scenarios, such as at grounding lines. Interactions with other climatic components Ice sheets interact with the surrounding atmosphere, ocean and sub-glacial earth. All of these interactive components need to be included to be able to have a comprehensive ice-sheet model. Basal Conditions play an important role in determining the behavior of ice sheets. The basal thermal state (if the ice is thawed or frozen) and the basal topography are difficult to map. The most favored method is to apply mass conservation constraints. For long-term projections, it is important to project the topography onto the continental shelf or into the fjords, and this can be difficult when the sub-glacial topography is not well-known. Summer Insolation drive temperature responses that have an effect on the rate of melting and mass balance of the ice sheet. For example, the dependence of ice volume on summer insolation can be represented with , where I is ice volume, is the rate of change of ice volume per unit of time, T is the response time of the ice sheet and S is the insolation signal. Air Temperature is needed in a model as it informs surface melt and runoff rates. For example, surface air temperature can be expressed with latitude 'lat', surface elevation h and