Biological sex, that is the possession of a functional testes or ovary, is a dichotomous phenotypic trait that can be determined by genotype, environment or the interaction of genotype and environment. Species with temperature-dependent sex determination (TSD) are thought to be particularly vulnerable to changing climate, whereas species with genetic sex determination relatively unaffected in sex ratio skew from rapid climate change. However, in some reptiles, sexual development under the influence of ZZ/ZW sex chromosomes is reprogrammed by incubation temperature to cause sex reversal of the homogametic sex. Hence rapid climate change may have unanticipated impacts on sex ratio skew and population viability in a much wider range of reptile species than previously thought. The mechanisms underpinning this reprogramming of sexual development are poorly understood, but recent work in our lab and others indicates that highly conserved and ubiquitous mechanisms of chromatin modification by temperature impact on the expression of key sex genes and thus sexual fate in these species.