The slowness with which the temperature of a body approaches that of its surroundings. ‘The Earth’s climate system has considerable thermal inertia. The effect of the inertia is to delay the atmospheric and oceanic response to various climate forcings. The existence of thermal inertia implies that still greater climate changes will be in store for present increased atmospheric CO₂ levels, which may be difficult or impossible to avoid’ (Lockwood in J. Holdem 2012).