Although temperate japonica rice (Oryza sativa L.) production is limited by both low‐ and high‐temperature stresses, the primary constraint was reported to be cold stress in the past. However, the magnitudes of low‐ and high‐temperature stresses may have been altered by global warming. In this study, the major climatic constraints to the yield and yield components of temperate japonica rice grown in field conditions under the current climates were assessed using the random forests method with 14‐yr field trial data (n = 499). Low temperatures had negligible impacts on rice yield under the current climates (2005–2018) in South Korea. Meanwhile, high‐temperature stress was most significant during the ripening stage, followed by the reproductive stage. Yield losses by high temperatures were primarily associated with reduced filled‐grain percentage, followed by reduced 1,000‐grain weight. During the vegetative stage, higher temperature (or higher growing degree days, GDD) decreased the number of panicles per m2 and increased the number of spikelets per panicle, resulting in negligible changes in the number of spikelets per m2 and yield. The effect of solar radiation was most significant during the ripening stage. More solar radiation during the ripening stage enhanced rice yield by increasing filled‐grain percentage and 1,000‐grain weight. This study highlights that the primary constraints to temperate japonica rice grown under the current climates are high‐temperature stresses during the ripening and reproductive stages rather than low‐temperature stresses. Thus, there is an urgent need to explore options for improving the adaptation of temperate japonica rice to anticipated global warming.