Sea surface temperature is projected to continue rising, and the ability of a species to persist largely depends on their thermal tolerance. Previous works have argued that tropical species have small thermal safety margins, and are therefore, more vulnerable to warming. One key factor in determining vulnerability is the potential of rapid evolution. Here we reviewed over 400 studies that investigate thermal tolerance of marine organisms and computed the microevolutionary rates based on existing population variance. Contrary to the notion that tropical species are more at risk, the estimated Haldane numerators from over 30 species did not show significant difference between geographic regions. Despite the urgency of this subject, our work also highlights the scarcity of studies that measure thermal tolerance from multiple populations. To better predict responses of marine organisms to future ocean conditions, information on both physiological limits and intra-specific variations are crucial.