Over the past 30 years, sea ice in the Arctic has declined by 3-4% per decade, making the Arctic the area experiencing the most rapid ecological changes due to climate change. Understanding the consequences of climate change on the Arctic ecosystem is therefore part of the European Union’s (EU) wider efforts. As a consequence of rapid sea-ice loss and increasing temperatures, the abundance, diversity and distribution of low trophic level organisms will be inevitably altered, generating cascading effects through the entire marine food chain from phytoplankton to apex predators. Despite their crucial role as bio-indicators of the Arctic marine ecosystem, the capacity of Arctic cetaceans to adjust their behaviour (foraging, movement patterns) and physiology (fat storage, thermoregulation) to climate-induced perturbations remains poorly understood. By compiling a multi-species long-term dataset covering 25 years and including 2 Arctic (narwhal and bowhead whale) and 2 sub-Arctic (humpback whale and harbour porpoise) apex predators, the WARMM project aims at investigating the behavioural and physiological responses of these species to climate change. The choice of the 4 cetaceans is based on their contrasting diet, habitats and level of activity, making this dataset unique to feed a comparative analysis of how these 4 species will cope with an imminent warming ocean. I will exploit a large existing dataset that will be augmented by physiological data collected during the project to (1) identify the foraging strategies from acoustic and accelerometry data, (2) link the behaviours and physiology to the environment, to finally (3) predict the future responses of apex predators in terms of thermal stress and geographical range. Our project will constitute an unprecedented scientific baseline to advise the EU and the Intergovernmental Panel on Climate Change in mitigating the effects of climate change and safeguarding the Arctic marine biodiversity.