Recent climate change should result in expansion of species to northern or high elevation range margins, and contraction at southern and low elevation margins due to extinction. Climate models predict dramatic extinctions and distributional shifts in the next century, but there are few ground-truths of these dire forecasts leading to uncertainty in predicting extinctions due to climate change. Previously, we reported on recent extinctions of Mexican Sceloporus lizards by comparing recent surveys to historical distributional records for 48 species at 200 sites. We also ground-truthed extinctions on five continents across 8 lizard families by comparing observed and predicted extinctions from an eco-physiological species distribution model and obtained a high R 2 of 0.72 (1, 2). Here, we derive more detailed predictions for 15 terrestrial reptile families and 142 species for the Mexican and California Biogeographic provinces using all known museum occurrence records, and detailed measures on eco-physiology. We adopt the eco-physiological model of extinction developed earlier but use a species-specific model. We predict massive and rapid extinctions of 22% of the reptile populations in Mexico within the next 50 years. We also predict that 3 of 15 reptile families, all three endemic to the Mexican and Californian biogeographic provinces, will go extinct by 2070, the hallmark of the beginnings of a mass extinction event. However, extinctions may be attenuated by forest cover and by presence of montane environments in contemporary ranges. We describe impacts of altitude on three species (Gopherus morafkai, G. evgoodei, and Gambelia sila) to illustrate regional management strategies (AZ-Mexico, Sinoloa, CA) for reserves in tandem with global strategies of CO2 limits that might limit climate impacts. By carefully selecting new montane preserves adjacent to desert and tropical forest habitats, and by implementing global controls on atmospheric CO2 emissions, extinctions may be reduced to less than 11% of species and only a single reptile family.