Earth’s climate has undergone tremendous change since the onset of the Industrial Revolution, due to anthropogenic activities. This significantly impacts ecosystem function, including marine ecosystems, which are responsible for ~50% of global primary productivity. Much of the marine productivity is supported by photosynthesis by microalgae, especially those comprising the phytoplankton. In this chapter, we explore how various components of climate change, including increased temperatures, increased carbon dioxide levels, ocean acidification, and shifts in light availability affect microalgal photosynthesis with a focus on microalgal pigments such as chlorophylls, carotenoids and phycobiliproteins. In addition to their role in harvesting light energy to drive photosynthesis, pigments can also play a role in protection against environmental stressors. We therefore also discuss how climate change affects the pigment composition, stability and production in microalgae. Such studies allow us to understand microalgal acclimation and adaptation to changing climatic conditions. The broader ecological impacts, such as shifts in microalgal populations and their functions, are also explored. Finally, we discuss conservation and mitigation strategies to protect microalgal populations, emphasizing the need for future study to mitigate climate change impacts.