By applying a single dataset (i.e., panel data at a national level) and a single analytical framework (i.e., a dynamic mathematical model), I compared religious (REL) and secular (SEC) ethics in two ways: as feasible strategies (i.e., with realistic parameter values such that a strategy can achieve its goal) and as reliable strategies (i.e., with a tight statistical relationship between a strategy and its goal). In both cases, the goal is to achieve environmental sustainability, but with different precepts and principles applied within different perspectives: global vs. local sustainability, individual feelings vs. social pressures as determinants of pro-environmental behavior, and long-run vs. short-run sustainability. Analytical results (feasibility) showed that REL are overall more feasible than SEC and, specifically, REL are more likely to affect the many pro-environmental behaviors required to achieve global sustainability, whereas SEC to affect some pro-environmental behaviors required to achieve local sustainability; REL are more likely to affect pro-environmental behaviors based on individual feelings and social pressures from small communities, whereas SEC to affect pro-environmental behaviors based on social pressures from large communities; REL are more likely to solve collective-action problems to achieve short-run sustainability, whereas SEC to solve collective-action problems to achieve long-run sustainability. Statistical results (reliability) based on 32 random- and between-effects regressions support these results and, particularly, REL and SEC were complementary in time (e.g., for REL, short-run sustainability is more reliable than long-run sustainability; for SEC, long-run sustainability is more reliable than short-run sustainability), in space (e.g., for SEC, local sustainability is more reliable than global sustainability), and in society (e.g., for REL, individual feelings are more reliable than social pressures).