A major research question for reef scientists is whether the accelerating rate of environmental change associated with global warming will exceed the capacity of coral species to adapt. While many authors claim that the genetic capacity of corals is exhausted, estimates of phenotypic variation and heritability in traits associated with thermal tolerance are rare. Here, we estimate variation in critical thermal maxima (CTmax) in two coral species: Porites cylindrica and Stylophora pistillata. We then use published estimates of generation times and per generation evolutionary rates to explore the capacity of these species to adapt to rising sea surface temperatures (SST). We estimate that between two and 7 decades will be required for these species to increase CTmax by 1.5°C. This range suggests these species can adapt to projected rises in SST of 2.0°C by the end of this century. However, more research is needed to determine empirically the heritability of these traits and generation times in coral species.