Kelps beds are distributed along polar and temperate coastlines worldwide and are one of the most productive ecosystems on earth. In recent years there have been increasing reports on changing kelps beds worlwide: either losses along whole coastlines, decrease or increase in biomass or also structural changes were documented and attributed to global change. During the current talk I will present evidence how an increase in summer and winter sea-surface temperatures may affect kelp beds through differential processes and how these abiotic changes may exert differential effects on either temperate or polar kelp beds. Two case studies will be in the focus of the talk. I will present evidence for the first time that sporophyte reproduction of kelps is the most sensitive life cycle process with respect to the factor temperature which conforms to ecological theory. In the summer reproducing kelp Laminaria digitata from the North Sea sporophyte recruitment became already affected in prevailing, sub-lethal summer temperatures which may increase in future. In the second example from the Kongsford, western Spitsbergen, I will demonstrate how a series of warmer ice free winters changed biomass and structural biodiversity of the local kelp bed system and thereby possibly overall productivity. Additional multi-factorial experiments on kelp spores provide first evidence how increased sedimentation rates and summer temperatures may affect kelp recruitment in future. Finally I will present some evidence about possible ecotypic adaptation of kelps along their distribution gradient and model expectations for the future.