Many ecosystems may be already experiencing temperatures near the limit for optimal plant growth (Topt). As the climate warms, temperatures may rise beyond what plants can tolerate, reducing their ability to grow and survive. Topt is characterized by measurements of air temperature near the ground (Tair), but the actual temperature of plant canopies (Tc) is often higher and more relevant for plant health and productivity. In this study, we use a new approach to better predict how Tc and Tair will change in the future. Our findings show that by the end of the century, Tc is likely to rise even more than Tair, and current climate models tend to underestimate this. Because temperature strongly affects plant growth and the exchange of water, energy, and carbon between the land and atmosphere, improving how models represent canopy temperature can lead to more accurate predictions of future climate impacts on ecosystems and the global carbon cycle.