Explain what a tipping point is in the climate system and provide an example.

• A. A tipping point is a threshold beyond which small changes cause large, potentially irreversible shifts; example: rapid ice-sheet collapse or shutdown of AMOC.
• B. A tipping point is the moment when CO2 emissions stop having an effect.
• C. A tipping point is a reversible seasonal fluctuation.
• D. A tipping point is a threshold beyond which small changes cause large, potentially irreversible shifts; an example is rapid ice-sheet collapse.

Answer: (D)

A tipping point is a threshold in a climate system where a small change pushes the system into a qualitatively different state, and the resulting shift can be large and hard to reverse on human timescales due to reinforcing feedbacks. This means crossing the threshold sets the system on a new trajectory even if the initial driver is relaxed. An example is rapid ice-sheet collapse, where destabilizing processes can suddenly accelerate ice loss and raise sea level quickly, with the change persisting long after the forcing is reduced. Other options misstate the idea—one describes no effect, another suggests a reversible seasonal change, or they don’t emphasize the threshold-driven, potentially irreversible nature.