  Catastrophic transitions, where a system shifts abruptly between alternate
steady states, are a generic feature of many nonlinear systems. Recently these
regime shift were suggested as the mechanism underlies many ecological
catastrophes, such as desertification and coral reef collapses, which are
considered as a prominent threat to sustainability and to the well-being of
millions. Still, the methods proposed so far for the prediction of an imminent
transition are quite ineffective, and some empirical and theoretical studies
suggest that actual transitions may occur smoothly, without an abrupt shift.
Here we present a new diagnostic tool, based on monitoring the dynamics of
clusters through time. Our technique discriminates between systems with local
positive feedback, where the transition is abrupt, and systems with negative
density dependence, where the transition is smooth. Analyzing the spatial
dynamics of these two generic scenarios, we show that changes in the critical
cluster size provide a reliable early warning indicator for both transitions.
Our method may allow for the prediction, and thus hopefully the prevention of
such transitions, avoiding their destructive outcomes.
