The cover shows a Sylvia’s leaf frog (Cruziohyla sylviae) in Costa Rica. The biological processes of ectotherms, such as amphibians, insects and fish, are directly affected by temperature, which means even small rises can cause significant problems. In this week’s issue, Johannes Overgaard and his colleagues examine the potential effects of climate change on these creatures. The researchers find that in the range of temperatures deemed as broadly survivable, for every rise in temperature of 1 °C, the rate of biological processes maintaining growth, homeostasis and ageing increases by 7%. But for every 1 °C rise in the range of temperatures deemed potentially dangerous, the rate of heat failure, which leads to death, increases by more than 100%. The team notes that this sensitivity to extreme heat in ectotherms is expected to lead to greater mortality as the frequency and intensity of heatwaves increases.