Dynamic Climate Risk and the Vulnerability Ratchet

Changing climate poses increasing risk to communities worldwide. Climate risk is a complex phenomenon that emerges from the interaction of physical, biological, and social systems. The dominant framework for assessing climate risk, developed across successive IPCC assessments, focuses on hazard, vulnerability, and exposure as contributing components of climate risk. This framework has organized research and policy productively, but it remains limited as it represents these components separate inputs evaluated at a single point in time. As a snapshot, it cannot capture path dependence, compounding, or irreversibility, the properties that make climate risk most difficult to address. To address this limitation, we introduce a Dynamic Climate Risk (DCR) framework that makes the coupling between risk components explicit and tracks their co-evolution over time. Analyzing the hazard–vulnerability coupling, we show that when hazard events outpace recovery, vulnerability fails to return to baseline and instead drifts upward in a self-reinforcing “vulnerability ratchet.” We derive the threshold event frequency at which the ratchet engages, and a lock-in vulnerability beyond which recovery capacity collapses, defining a finite policy window whose length we bound analytically. Mitigation remains essential over the long run, but because hazard is effectively fixed on near-term policy horizons while vulnerability and exposure are not, the most consequential near-term choices concern managing these couplings rather than emissions alone. We illustrate the framework with three cases, Bangladesh, the 2022 Pakistan floods, and the divergent trajectories of Haiti and Cuba, each exercising different parts of its structure.