Resilience indicators: prospects and limitations for early warnings of regime shifts

TLDR

In ecosystems near tipping points, recovery slows—a phenomenon called critical slowing down (CSD) that manifests as increased temporal correlation and variance, offering a potential early warning signal for regime shifts, though not all shifts involve tipping points. The authors review the literature to guide expectations about the reliability of CSD‑based early warning signals for critical transitions. They synthesize the growing body of work on CSD indicators to delineate when such signals are expected and when they are not.

Abstract

In the vicinity of tipping points—or more precisely bifurcation points—ecosystems recover slowly from small perturbations. Such slowness may be interpreted as a sign of low resilience in the sense that the ecosystem could easily be tipped through a critical transition into a contrasting state. Indicators of this phenomenon of ‘critical slowing down (CSD)’ include a rise in temporal correlation and variance. Such indicators of CSD can provide an early warning signal of a nearby tipping point. Or, they may offer a possibility to rank reefs, lakes or other ecosystems according to their resilience. The fact that CSD may happen across a wide range of complex ecosystems close to tipping points implies a powerful generality. However, indicators of CSD are not manifested in all cases where regime shifts occur. This is because not all regime shifts are associated with tipping points. Here, we review the exploding literature about this issue to provide guidance on what to expect and what not to expect when it comes to the CSD-based early warning signals for critical transitions.