What is the natural variability of our climate? This simple question is, in fact, very hard to answer, from either the theoretical or observational point of view. However, it is of utmost importance if we really want to detect and predict the consequences of human activities that have altered several components of the climate system, the most noticeable change being a considerable increase in atmospheric carbon dioxide from the burning of fossil fuels.
The climate system is complex because it is made up of several components (such as the atmosphere, oceans, and ice sheets), each of which has its own response times and thermodynamic properties. Those components not only interact nonlinearly with each other, but are connected to other complex systems such as the carbon cycle, which regulates greenhouse gas concentrations in the atmosphere. The climate can be affected by various types of so-called external forcings or influences (such as...
