Understanding how species' thermal limits have evolved across the tree of life is central to predicting species' responses to climate change. This study, using experimentally-derived estimates of thermal tolerance limits for over 2000 terrestrial and aquatic species, shows that variation in thermal tolerance is attributed to adaptation to current climatic extremes and evolutionary ‘attractors’ reflecting boundaries or optima in thermal tolerance limits. Results reveal deep-time climate legacies in ectotherms, with orders originating in cold paleoclimates having lower cold tolerance limits than those with warm thermal ancestry. Heat tolerance is unrelated to climate ancestry. Cold tolerance evolved more quickly than heat tolerance. Given the rate of climate change, adaptive responses in thermal limits will have limited potential to rescue most species.

Joanne M. Bennett, Jennifer Sunday, Piero Calosi, Fabricio Villalobos, Brezo Martínez, Rafael Molina-Venegas, Miguel B. Araújo, Adam C. Algar, Susana Clusella-Trullas, Bradford A. Hawkins, Sally A. Keith, Ingolf Kühn, Carsten Rahbek, Laura Rodríguez, Alexander Singer, Ignacio Morales-Castilla, Miguel Ángel Olalla-Tárraga