AFPs create a difference between the melting point and freezing point (busting temperature of AFP bound ice crystal) known as thermal hysteresis.  The addition of AFPs at the interface between solid ice and liquid water inhibits the thermodynamically favored growth of the ice crystal.  Ice growth is kinetically inhibited by the AFPs covering the water-accessible surfaces of ice.
Thermal hysteresis is easily measured in the lab with a nanolitre osmometer.  Organisms differ in their values of thermal hysteresis.  The maximum level of thermal hysteresis shown by fish AFP is approximately −3.5 °C (Sheikh Mahatabuddin et al., SciRep)(29.3 °F). In contrast, aquatic organisms are exposed only to −1 to −2 °C below freezing.  During the extreme winter months, the spruce budworm resists freezing at temperatures approaching −30 °C.
The rate of cooling can influence the thermal hysteresis value of AFPs.  Rapid cooling can substantially decrease the nonequilibrium freezing point, and hence the thermal hysteresis value.  Consequently, organisms cannot necessarily adapt to their subzero environment if the temperature drops abruptly.