We assessed the responses of solitary cells of Arctic Phaeocystis pouchetii grown under a matrix of temperature (2°C vs. 6°C), light intensity (55 vs. 160 μmol photons m-2 s-1) and pCO2 (400 vs. 1000 μatm). Next to acclimation parameters (growth rates, particulate and dissolved organic C and N, chlorophyll a content), we measured physiological processes in-vivo (electron transport rates and net photosynthesis) using fast-repetition rate fluorometry and membrane-inlet mass spectrometry. Within the applied driver ranges, elevated temperature had the most pronounced impacts, significantly increasing growth, elemental quotas and photosynthetic performance. Light stimulations manifested prominently under high temperature, underlining its role as a 'master variable'. pCO2 was the least effective driver, exerting mostly insignificant effects. The obtained data were used in a simplified ecosystem model to simulate P. pouchetii's bloom dynamics in the Fram Strait with increasing temperatures over the 21st century. Model results suggest that global warming will accelerate bloom dynamics, with earlier onsets of blooms and higher peak biomasses. Despite remaining uncertainties about the magnitude of these effects, data strongly suggest that increasing temperatures over the coming century will affect the phenology of Phaeocystis and other Arctic phytoplankton with likely important implications for higher trophic levels.