The polar bear is part of the Arctic ecosystem and a food web through which carbon cycles. The ecosystem comprises phytoplankton, algae, a variety of animals and the natural environment.
The polar bear itself has no natural predators within its ecosystem and is thus supported by every other member of it, from the phytoplankton and algae that convert carbon dioxide from the ocean into organic carbon tissue to fish that feed on them, walruses and whales.
Unfortunately, scientific knowledge of the Arctic ecosystem is limited, owing to its inhospitable weather and the expense of mounting expeditions. Nevertheless, research has demonstrated conclusively that global warming is gradually and irrevocably destroying it.