  Among the properties that are common to complex systems, the presence of
critical thresholds in the dynamics of the system is one of the most important.
Recently, there has been interest in the universalities that occur in the
behavior of systems near critical points. These universal properties make it
possible to estimate how far a system is from a critical threshold. Several
early-warning signals have been reported in time series representing systems
near catastrophic shifts. The proper understanding of these early-warnings may
allow the prediction and perhaps control of these dramatic shifts in a wide
variety of systems. In this paper we analyze this universal behavior for a
system that is a paradigm of phase transitions, the Ising model. We study the
behavior of the early-warning signals and the way the temporal correlations of
the system increase when the system is near the critical point.
