The most important fluxes in the climate system are those of radiant (solar and heat) energy, but the fluxes of water and, to a lesser extent, mass (matter) also affect climate. Net fluxes differ considerably as a function of the time and space period considered and different budgets, the result of the net fluxes, are established when the controlling conditions change. A climate change occurs either because the forcings imposed on the planet change or because the dynamics of the system cause internal variations in fluxes and budgets. Forcings are caused by variations in agents outside the climate system such as solar radiation fluctuations or variations in components of the climate sys-
tem such as volcanic eruptions, ice-sheet changes, carbon dioxide (C02) increases and deforestation. Such alterations in forcings are modified by feedback effects within the climate system.