Wang, J., Cheung, M., Rasooli, L., Amirsadeghi, S. and Vanlerberghe, G. C. 2014. Plant respiration in a high CO₂ world: How will alternative oxidase respond to future atmospheric and climatic conditions? Can. J. Plant Sci. 94: 1091-1101. Plant mitochondria contain an alternative oxidase (AOX) that reduces the energy yield of respiration. While respiration and photosynthesis are known to interact, the role of AOX in the light remains poorly understood. This gap in our understanding of leaf metabolism extends to future conditions of high CO₂ and climate change. While studies indicate that AOX respiration is quite responsive to growth conditions, few studies have examined AOX respiration at high CO₂ and little is known regarding the combined impact of changes in both CO₂ and other climatic factors such as temperature and water availability. Given its non-energy conserving nature, a fundamental response by AOX to these future conditions could impact the net carbon gain that results from the combined processes of photosynthesis and respiration. Here, we show that leaf AOX protein amount in Nicotiana tabacum is dependent upon growth irradiance and CO₂ level, that AOX is subject to biochemical control by intermediates of photorespiration, and that photosynthesis is impacted in transgenic plants lacking AOX. We also review findings that tobacco AOX respiration is responsive to climatic variables (temperature, water availability), thus providing an excellent experimental system to investigate the interplay between AOX, photosynthesis at high CO₂, and climate change.