Tipping points in the climate system

Thresholds in parts of Earth’s climate system beyond which small disturbances can trigger large, self-reinforcing shifts. These shifts may persist even if the original disturbance is reduced.

Positive feedback: A process in which a change produces effects that amplify the original change. Amplifying feedbacks can push climate components across thresholds.
Greenland ice sheet: The vast body of land ice covering most of Greenland. Sustained ice loss could become self-reinforcing through surface lowering and warming.
Tipping element: A large component of the Earth system that can shift into a markedly different state after a threshold is crossed. Climate tipping points are thresholds associated with changes in these components.
Sea-level rise: A sustained increase in the average level of the ocean relative to land. Large ice-sheet losses following a transition would add to long-term sea-level rise.
Hysteresis: Dependence of a system’s state on its history, often producing different thresholds for change and recovery. Some climate shifts require much more cooling to reverse than warming to trigger.
West Antarctic Ice Sheet: The Antarctic ice sheet resting largely on bedrock below sea level in West Antarctica. Marine ice-sheet instability could drive substantial, long-lasting sea-level rise.
Bifurcation: A qualitative change in a system’s possible states as a control parameter varies. Bifurcation theory formalizes how gradual forcing can alter system stability.
Permafrost carbon cycle: The exchange of carbon among frozen ground, ecosystems, and the atmosphere as permafrost thaws and refreezes. Thaw can release greenhouse gases that add warming and increase further thaw.
Critical slowing down: A slowing recovery from disturbances as a system approaches a critical transition. Longer recovery times can signal declining resilience before a threshold is crossed.
Atlantic meridional overturning circulation: A system of Atlantic Ocean currents that transports heat northward and returns deep water southward. Freshwater input and warming may weaken its circulation, with consequences across regions.

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