The polar bears are happy and free. They can move around everywhere with no worry of the ice melting.
A factory is introduced to the polar bears habitat and the ice starts melting and the sun also makes the ice melt which then makes it hard for the polar bears to go anywhere because there is water and they start dying because they fall into water.
More factories are introduced to the polar bears habitats and more ice starts to melt which then starts to kill more and more polar bears. The last two polar bears on the planet are left.
Almost all the ice has melted because of the suns heat and also the factories. At this point the polar bears are extinct because they can not breed anymore.
All the polar bears have been wiped out from planet earth and are now known as extinct.