**Abstract**

The intense agricultural and human being activities, especially after the industrialization era, have increased the CO2 concentration, which led to changes in the global climate. Climate change and its consequences, that is*,* elevated CO2, water stress, and extreme temperatures, have induced many biotic and abiotic stresses and have caused alterations in plant physiology, leading to a reduced photosynthetic capacity of plants. Photosynthesis is the most crucial biochemical process in plants that determines the final dry matter production and productivity of plants. The efficiency and status of the photosynthetic apparatus can be measured by the measurement of chlorophyll fluorescence. Measurements of chlorophyll fluorescence are easy, non-destructive, and quick, and it reflects changes in the general bioenergy status of a plant. Studies have indicated that abiotic stresses emerging from climate changes cause changes in the biological processes of plants and damage the internal structure of photosynthesis and control of the cellular process. Chlorophyll fluorescence, meanwhile, is an effective parameter and an indicator of photosynthetic status and its mechanisms under stressful conditions. Therefore, the photosynthetic changes and adaptation and the role of chlorophyll fluorescence in determining its status under climate change are discussed in this chapter.

**Keywords:** abiotic stress, chlorophyll fluorescence, drought, elevated CO2, extreme temperatures, leaf physiology
