As the ocean is changing, the environment of phytoplankton will change in very different ways. Increased atmospheric CO₂ leads to warming of the air and the surface ocean, but also to uptake of inorganic carbon by the ocean (called ocean acidification). The warming of the ocean results in increased stratification, which means that the light climate of algae and the nutrient supply will both change. While a fair amount of data exists that indicates how phytoplankton might respond to a shift in one environmental parameter, like temperature or light, we have no conceptual framework on the response patterns to several simultaneous shifts. The effects of different simultaneous changes in environmental conditions are not additive, but interact in a complex fashion. Within this multiple stressor project, funded by NSF, we and our collaborators will investigate the response patterns of several species of phytoplankton to simultaneous changes in temperature, light, nutrients and the carbonate system. This type of data is urgently needed as input for models predicting the consequences of global change on primary production.