Synthesis Group: Using thermal tolerance limits to understand species susceptibility under climate change

All organisms have characteristic thermal tolerance ranges, an upper and lower temperature threshold beyond which physiological damage occurs. Extreme temperature events now are commonplace and predicted to increase in frequency and intensity and to occur at unusual times. These events impact both survival and performance of organisms, either directly or in conjunction with other factors like drought, competition, or other sources of resource limitation. Thus, to understand the implications of breaching thermal thresholds and effectively predict species vulnerability under climate change, requires a nuanced understanding of what it means for an organism to be thermally tolerant. Notably, thermal tolerance will likely mean different things across biomes and taxa – animals vs plants, for example. Thermal tolerance is also historically examined in different ways across taxa – e.g. temperatures that result in knock-down vs kill vs leaf drop or impaired seed-set. Further, even for a single species, thermal tolerance may vary across time, space, and genetic profile.