For phytoplankton, to cope with environmental change, trait variability and phenotypic plasticity may play an important role. Since environmental change includes simultaneous changes in abiotic parameters, we assessed the impact of multiple drivers on functional traits of the diatom Thalassiosira weissflogii by manipulating concurrently temperature, pCO2, and the dissolved nitrogen:phosphorus (N:P) ratio based on predictions from the Intergovernmental Panel on Climate Change (IPCC) reports for 2100. In a batch culture experiment with one strain of T. weissflogii (Grunow) Fryxell & Hasle (SAG, strain number 122.79), we tested three scenarios: ambient (ambient temperature and atmospheric pCO2; 16 N:P ratio), moderate future scenario (+1.5°C and 800 ppm CO2; 25 N:P ratio), and more severe future scenario (+3°C and 1000 ppm CO2; 25 N:P ratio). Each treatment contained six replicates. We applied flow cytometric measuring (BD Accuri C6) on a single-cell level to investigate trait variability and phenotypic plasticity within one culture. All cell cultures were measured daily. The forward scatter (FSC) was used to assess changes in cell size, the fluorescence detectors FL3 (670nm) and FL4 (675nm) provide information about the chlorophyll a content of the cells. The lipid and protein content was measured five times during the experiment, twice in the exponential growth phase and the stationary phase as well as once in the transition phase. To determine the lipid content of the cells, we used the stain Nile Red and the staining signal was detected with the fluorescence detectors FL2 (585 nm) and FL3 (670 nm) for the non-polar and polar lipids. The signal of FITC for the Protein content of the cells was detected with the fluorescence detector FL1 (533 nm). We used the coefficient of variation (CV) of each flow cytometric measurement to determine cell-to-cell variability.