The cold of the Arctic regions is linked to two reasons: the sunshine is less intense in duration and intensity and - when the sun returns - the whiteness of the snow/ice limits the effects of its rays by returning them towards the atmosphere through a mirror phenomenon called 'albedo'. During the winter period of darkness, the whole arctic zone stores cold through the thickening of the pack ice and the freezing of the ground which persist beyond the first very low rays of the spring sun.