Increasing the CO₂ concentration around plant leaves is known to cause partial stomatal closure, which can reduce transpirational cooling and raise leaf temperatures. To determine the degree of this effect with cotton under free-air CO₂ enrichment (FACE) conditions, measurements of foliage temperature were made with an infrared thermometer on cotton in the large cooperative FACE experiment conducted at the University of Arizona Maricopa Agricultural Center during the 1989 growing season.