Abstract: Elevating atmospheric CO₂ concentration greatly affects global climate changes and the development and production of crops. Stomatal closure can be induced by high concentration CO₂ and improves the plant’s adaptation to elevated levels of atmospheric CO₂. However, the mechanism is still unclear. Using infrared thermography, we isolated an Arabidopsis mutant ecs1. Genetic analysis revealed that the mutant is controlled by a single recessive nuclear gene. Map-based cloning revealed that the mutant gene encodes an integral membrane protein that homologizes with calcium transporter. Compared with wild-type Arabidopsis, ecs1 showed stomatal closure and increased leaf temperature under 360 μL·L^–1CO₂. ecs1 had enhanced adaptation to stress of 900 μL·L^–1CO₂ for a long time. In addition, ecs1 produced more H₂O₂ under 360 μL·L^–1CO₂ than wild type. Under 900 μL·L^–1CO₂, both ecs1 and wild type produced more H₂O₂. Therefore, H₂O₂ mediates CO₂-induced stomatal closure and is involved in the ECS1 signal pathway in Arabidopsis.