The direct impacts of climate change on crop yields and human health are both well-studied, but the interaction between the two have received little attention. Here we analyze the consequences of global warming for agricultural workers and the crops they cultivate using a global economic model with explicit treatment of the physiological impacts of heat stress on humans’ ability to work. The agricultural impacts literature has mostly focused on the effects of climate change on crop yields. However, we find that labor force impacts are equally important up to +3C warming, relative to the 1986-2005 baseline, and these overlooked impacts are dominant in Sub-Saharan Africa and Southeast Asia. In those regions, heat stress with 3C global warming could reduce labor capacity in agriculture by 30-50%, boosting food prices and requiring much higher levels of employment in the farm sector.