In temperate and polar rocky coastal ecosystems, kelps form the base of complexly structured and highly diverse species associations. In recent years, kelp forests worldwide have faced extinction at their equatorward limits and models have predicted a poleward shift of kelp ecosystems during climate change. To gain an understanding of local thermal adaptation and response plasticity in a forest-forming kelp species, we assessed populations of Laminaria digitata along its entire European distribution range from Brittany to Spitsbergen for their capacity to withstand high temperature stress, and connected physiological results to population genetics. Although the overall heat response was similar across the distribution range, we identified subtle adaptions reflecting the long-term local temperature history in one northern and one southern population. Additionally, we investigated the potential role of transgenerational plasticity (TGP, i.e. effects of parental environment on offspring traits) as a means of fast response to a warming environment between haploid gametophyte parents and diploid sporophyte offspring of L. digitata. Our results show TGP for the first time in a kelp, in that not the 15°C, but the 5°C gametophyte parent treatment enhanced juvenile sporophyte offspring growth. In this talk, I will conceptualize the thermal response of L. digitata and discuss our results within the framework of global warming.