The environmental changes caused by global warming will affect many organisms worldwide (Huey et al. (2010) Science 328:832-833). At first glance ‘heterothermic’ species, which are those that enter daily torpor or hibernation (multiday torpor), may appear to be most threatened because torpor is characterised by pronounced reductions of metabolism and body temperatures and therefore requires low temperatures to maximise energy savings. Seasonally hibernating species are potentially vulnerable because many have a well-defined winter dormancy that is closely synchronised with historical phenological patterns and may be unable to appropriately adjust their behaviour and physiology to the altered environment. Moreover, a change of climate may increase the energetic costs of hibernation and lead to the extinction, especially of species restricted to ‘sky islands’ with limited mountain habitats. In contrast, many other heterothermic species express torpor opportunistically and effectively at any time of the year including in summer. Opportunistic torpor can also be used to deal with environmental disasters such as cyclones and fires predicted to increase with climate change. As use of torpor reduces foraging requirements and therefore exposure to predators, which often invade areas after adverse events, and because heterothermic mammals generally have longer lifespans than related homeotherms (cannot use torpor), heterotherms will have an increased chance to cope with adverse periods. Consequently, those heterothermic species with plastic energetic requirements may also stand a better chance of survival than do homeotherms in a world with changing environmental conditions and greater climatic extremes.