Extreme escalation of heat failure rates in ectotherms with global warming.

Temperature affects the rate of all biochemical processes in ectotherms 1,2 and is therefore critical for determining their current and future distribution under global climate change 3-5 . Here we show that the rate of biological processes maintaining growth, homeostasis and ageing in the permissive temperature range increases by 7% per degree Celsius (median activation energy E a  = 0.48 eV from 1,351 rates across 314 species). By contrast, the processes underlying heat failure rate within the stressful temperature range are extremely temperature sensitive, such that heat failure increases by more than 100% per degree Celsius across a broad range of taxa (median E a  = 6.13 eV from 123 rates across 112 species). The extreme thermal sensitivity of heat failure rates implies that the projected increase in the frequency and intensity of heatwaves can exacerbate heat mortality for many ectothermic species with severe and disproportionate consequences. Combining the extreme thermal sensitivities with projected increases in maximum temperatures globally 6 , we predict that moderate warming scenarios can increase heat failure rates by 774% (terrestrial) and 180% (aquatic) by 2100. This finding suggests that we are likely to underestimate the potential impact of even a modest global warming scenario.