How will organisms deal with Climate change? Ectotherms such as reptiles and amphibians are especially at risk due to their metabolic ties to the environment and their general inability to migrate with changing climates over short time frames. We modeled the growth response of Three-toed Box Turtles (Terrapene carolina triunguis) to fluctuations in ambient temperature and precipitation. Then we extrapolated this model to climate conditions expected in 2100. We predict that there is less than 20% possibility of hatchling turtles growing during their first year. Reduced annual growth rates during later years may cause earlier termination of growth, smaller standard carapace lengths, and reduced fecundity. These responses are typical of those that stimulate an extinction vortex. These findings provide for a general understanding of how this species and other terrestrial reptiles may respond to climate change. Without reduction in greenhouse gas emissions we could face catastrophic declines in many ectotherms as temperature and rainfall patterns change.