The tropics have dynamics and features that are different from the other parts of the climate (midlatitudes, upper latitudes). In the tropics, a good amount of the circulation is driven by condensation. In the tropics, the amount of sunlight that is received does not vary as much as in the midlatitudes. The tropics can generate features, such as tropical cyclones, the Intertropical convergence zone, or El Nino/La Nina that heavily influences the midlatitudes.

Climate forcing, on the other hand, is a general term that describes the mechanics of the atmosphere at large. These include heat transport by ocean gyres, aerosols, and greenhouse gas forcing. Now one can make the argument that this distinction between tropics and extratropics is semantic, which is fair. But it follows in the methodological reductionism of science to break the climate system by geography.