Cyanobacterial blooms are becoming more common in freshwater ecosystems due to climate-change induced warming and eutrophication. These shifting environmental conditions introduce multiple simultaneous stressors, such as increased temperature and irradiance, which can have a non-linear, synergistic effect on the productivity of bloom-forming cyanobacteria. Here, we examined the combined effects of thermal stress and light on the growth and photophysiology of Microcystis aeruginosa (UTEX-LB-2386). This strain was monitored across five temperatures (20-40 °C) and three light regimes in a batch culture setting. Growth was measured via optical density and PAM fluorometry assessed in-vivo chlorophyll (F0), maximum quantum yield of Photosystem II (QYmax, a proxy for photosynthesis efficiency and cell stress), and relative electron transport rates across PSII (a proxy for photosynthesis). A thermal optima (TOPT) for growth was observed at 30°C under low light, but shifted to 25°C as light levels increased. The thermal optima (TOPT) for QYmax and rETR was inconsistent with the optima for growth, and was observed at 25°C under low light, but shifted to 20°C as light levels increased. Our results thus indicate that growth and photophysiology in M. aeruginosa is decoupled, and could have implications for bloom formation, carbon allocation, and toxin production by some toxin-producing strains of M. aeruginosa in a warming world.