Extreme heat can accelerate wheat aging — an effect that reduces crop yields and is currently underestimated in most crop models — according to a study published online this week in Nature Climate Change. These findings imply that climate warming presents even greater challenges to wheat production than current models predict. An important source of uncertainty in anticipating the effects of climate change on agriculture is limited understanding of crop responses to extremely high temperatures. David Lobell and co-workers used satellite measurements of wheat growth in northern India to monitor the rates of wheat aging — known as senescence — following exposure to temperatures greater than 34 °C. Simulations with two commonly used crop models suggest that existing models underestimate the effects of heat on senescence. Because the onset of senescence is an important limit to grain filling, and therefore grain yields, crop models likely underestimate yield losses. These findings suggest that the effectiveness of agricultural adaptations will depend on how well they reduce crop sensitivity to very hot days.