Box 10.1, Figure 1. Schematic illustration of various responses of a climate variable to forcing. The forcing (top panels) reaches a new stable level (left part of figure), and later approaches the original level on very long time scales (right part of the figure). The response of the climate variable (bottom panels) can be smooth (solid line) or cross a tipping point inducing a transition to a structurally different state (dashed lines). That transition can be rapid (abrupt change, long-dashed), or gradual (short-dashed), but is usually dictated by the internal dynamics of the climate system rather than the forcing. The long-term behaviour (right part) also exhibits different possibilities. Changes can be irreversible (dash-dotted) with the system settling at a different stable state, or reversible (solid, dotted) when the forcing is set back to its original value. In the latter case, the transition again can be gradual or abrupt. An example for illustration, but not the only one, is the response of the Atlantic meridional overturning circulation to a gradual change in radiative forcing.