Climate change would largely offset labor capacity increment fueled by China’s two-child policy

China’s implemented two-child policy (TCP) was aimed at countering the economic challenges posed by an aging population. However, the impact of climate change on the goal of this policy remains uncertain. This study examines how climate change induced heat stress may impact the productivity of the working-age population, measured as total working hours as a result of the TCP. The TCP is projected to increase total working hours of China by 12%–19% under three scenarios compared to the previous one-child policy during 2071–2100. This increase is completely negated by a 19%–29% decrease in the total working hours induced by reduction in labor capacity from heat stress under climate warming. Specifically, compared to the one-child policy (OCP) in the 2071–2100, the total working hours shows the largest increase of 19% contributed by TCP but it can decrease by 9% if climate change is considered under the SSP370 scenario. Likewise, the TCP benefits can be totally offset by climate change which finally leads to 6% and 11% less than OCP under the SSP126 and SSP585 scenarios, respectively. Climate change’s adverse effects are particularly pronounced (30% or larger decrease in the total working hours under SSP370) in eastern and southern China, which has the most developed economy. Given China’s labor-intensive economic model, this study underscores the need for urgent mitigation strategies to safeguard the nation’s future economic well-being.