The Earth's system is characterized by the interaction of processes that take place on molecular (very small) and planetary (very large) spatial scales, as well as on short and long time scales. Before scientists may begin their work with these data, it is important that they understand what the data are.

In addition to the changes brought about by natural forces, it has recently become apparent that a relative newcomer to planet Earth — the human being — has become a powerful agent of environmental change.

Background information on the El Nino Southern Oscillation or ENSO.