Here we analyze the consequences of global warming on agricultural crop yields and the people employed in their production using a global economic model with explicit treatment of the physiological impacts of heat stress on humans ability to work. While most of the agricultural impacts literature has focused on the effects of climate change on crop yields, we find that global labor force impacts dominate. This dominance is particularly striking at intermediate levels of warming (+2C to +4C) where apparent welfare gains in some regions are reversed, becoming significant losses once labor force impacts are considered. The losses are particularly pronounced in Africa, South- and Southeast Asia. There, heat stress at +3C means labor capacity in agriculture could fall by 20 – 30%, boosting food prices and requiring much higher levels of employment in the farm sector.