A main concern in marine ecology is understanding the mechanisms driving responses of biological systems to environmental fluctuations. A major issue is that each biological system (e.g. organism, ecosystem) experiences fluctuations according to its own intrinsic characteristics. For instance, how an organism experiences a thermal fluctuation, i.e as a long marine heatwave or as a mild pulse, depends on its thermal tolerance and developmental time, which can vary as the fluctuation is experienced. Here, I explore a geometric approach, considering the biological perspective. Environmental fluctuations are represented as points in a “space of fluctuations”. The biological perspective is then defined as a coordinate frame within that space. Coordinates are given by components (e.g. amplitude and time scale) characterising each environmental fluctuation, which are then transformed into biological scales, using biological traits (tolerance and biological time). Using simulations of organisms growing under thermal fluctuations with different characteristics, I show how this approach: (1) Enables to integrate physiology and phenology to better interpret biological responses to fluctuating environments. (2) Improves understanding of the role of adaptive plasticity as a rescue effect. (3) Facilitates understanding the effects of thermal fluctuations on additional organismal traits (e.g. body mass). I also discuss wider applications in the context of species persistence, coexistence, biodiversity, and ecosystem function in scenarios of extreme fluctuations.