Nearly all of the major kinds of life, divisions of life, phyla of animals, occur in the sea. Only about half of them can make it to land or freshwater.
Sylvia EarleFor humans, the Arctic is a harshly inhospitable place, but the conditions there are precisely what polar bears require to survive - and thrive. 'Harsh' to us is 'home' for them. Take away the ice and snow, increase the temperature by even a little, and the realm that makes their lives possible literally melts away.
Sylvia Earle