Polar Bear

A Climate-Constrained Apex Predator at the Top of the Marine Food Web

The polar bear is the world's largest terrestrial carnivore — a marine mammal under U.S. law for its sea-ice-dependent ecology. Ursus maritimus is listed as Vulnerable on the IUCN Red List with a global population estimated at 22,000–31,000 individuals across 19 subpopulations [Wiig et al. 2015]. The species is the principal modern symbol of climate change's biodiversity impact: every dimension of polar bear ecology — hunting, breeding, migration, condition — depends on sea-ice extent and timing, both of which are declining at well-documented rates across the Arctic [IPCC AR6 2021 chapters on cryosphere].

The species' formal protection under the U.S. Endangered Species Act (Threatened, May 2008) was the first listing under the ESA that explicitly identified greenhouse-gas-driven climate change as the operative threat — establishing the legal precedent for similar listings of climate-vulnerable species [USFWS 2008].

Biology and identification

Ursus maritimus adults reach 2–3 m in length and 350–700 kg (males) or 150–250 kg (females) [Stirling 2011]. The fur is hollow-shafted and translucent, scattering visible light to appear white. Skin underneath is black. Specialised adaptations to the Arctic marine environment: a thick fat layer; webbed forepaws for swimming; non-retractable claws for traction on ice; a 5+ cm-thick blubber layer that doubles as both insulation and energy reserve.

The species' diet is approximately 90% seals — primarily ringed seal (Pusa hispida) and bearded seal (Erignathus barbatus), hunted at breathing holes and on sea ice. Polar bears cannot effectively hunt in open water; they are obligate ice-platform hunters [Stirling 2011]. When sea ice retreats from the continental shelf in summer, bears in many subpopulations move to land and enter an extended fasting period (3–4 months in normal years; longer in warming-year sea-ice scenarios). Body condition declines linearly with the duration of the on-land fasting period.

Females first reproduce at 4–6 years; gestation is approximately 8 months with 1–3 cubs per litter every 2–3 years. Cubs remain with their mother for 2–2.5 years before independence.

Habitat and range

Circumpolar Arctic distribution across five nations: the United States (Alaska), Canada, Greenland (Denmark), Norway (Svalbard), and the Russian Federation. The IUCN Polar Bear Specialist Group recognises 19 subpopulations distributed around the Arctic basin, each with separate status assessments [Polar Bear Specialist Group 2024]:

• Declining at recent assessment: Southern Beaufort Sea, Western Hudson Bay, Kane Basin
• Stable: Baffin Bay, Davis Strait, Foxe Basin, Gulf of Boothia, Lancaster Sound, M'Clintock Channel, Northern Beaufort Sea, Norwegian Bay, Southern Hudson Bay, Viscount Melville Sound
• Increasing: M'Clintock Channel (recovering after past over-harvest)
• Data Deficient: Arctic Basin, Chukchi Sea, East Greenland, Kara Sea, Laptev Sea, Barents Sea (some recent assessments suggest decline but data limited)

The principal habitat is sea ice — pack ice for hunting, fast ice (sea ice attached to shore) for maternal denning in some populations, and on-shore denning in others.

Conservation status

Ursus maritimus is listed as Vulnerable on the IUCN Red List, with population trend uncertain (some subpopulations declining, others stable, some data-deficient) [Wiig et al. 2015]. Listed as Threatened under the U.S. Endangered Species Act since May 2008 [USFWS 2008]. CITES Appendix II — international commercial trade in polar bear parts requires permits.

The U.S. ESA listing was contested by some Arctic-state governments at the time as overly precautionary. Subsequent satellite and on-bear telemetry research has reinforced rather than weakened the underlying scientific concern. The 2015 IUCN reassessment retained the Vulnerable category.

Threats

Sea-ice loss driven by climate change is the structural threat. Arctic sea-ice extent has declined 12.6% per decade in September minimum extent since 1979 (NSIDC long-term record) [NSIDC 2024]. The decline affects polar bears through:

• Reduced hunting access — fewer days per year on suitable hunting ice
• Longer on-land fasting periods — bears in southern Hudson Bay now spend approximately a month longer on shore than in the 1980s baseline [Stirling et al. 2011]
• Body condition decline — measured reductions in adult body mass and cub survival in long-term-monitored populations
• Population-level demographic stress — recruitment failures documented in the Western Hudson Bay and Southern Beaufort Sea subpopulations

Subsistence harvest by Indigenous Arctic communities is regulated under national management frameworks (the U.S. Marine Mammal Protection Act; Canada's provincial/territorial wildlife management; analogous frameworks in Greenland, Russia, Norway). Sustainable take is established by quota systems for each subpopulation. Indigenous harvest is not the primary threat under contemporary management.

Industrial development — oil and gas exploration, shipping route expansion through the Arctic, mining infrastructure — affects denning habitat, contaminant exposure (particularly persistent organic pollutants that accumulate up the marine food web), and bear-human conflict in onshore zones.

Trophy hunting is permitted in Canada under provincial/territorial quotas, drawing some international hunters; subject to ongoing controversy over conservation impact.

What is being done

• IUCN/SSC Polar Bear Specialist Group — the principal scientific coordination body across the five range-state governments. Publishes subpopulation status assessments approximately every 5 years.
• Polar Bear Range States Agreement (2009 Memorandum of Understanding) — Canada, Greenland (Denmark), Norway, Russia, and the United States coordinate conservation through periodic Range States meetings.
• U.S. Fish and Wildlife Service Polar Bear Recovery Plan — 2016 plan implementing the ESA Threatened listing; principal U.S. conservation framework.
• Polar Bears International — the principal U.S./Canadian NGO supporting research, public education, and the Arctic Ambassador Centers network at zoos and aquariums.
• WWF Arctic Programme — supports cross-national polar bear work, particularly on bear-human conflict reduction in Indigenous communities.
• Climate policy is polar bear policy. The IPCC AR6 documentation of cryosphere change is the most-cited scientific basis for polar bear projections [IPCC 2021].

How readers can help

• Climate policy engagement is the highest-leverage action. Polar bear recovery is impossible under continued sea-ice loss regardless of any other conservation measure.
• Support Polar Bears International, WWF Arctic Programme, and the Polar Bear Specialist Group. Direct funding supports the multi-decade tagging, monitoring, and bear-human-conflict reduction work.
• For Arctic travellers: choose operators with documented polar-bear-safe practices (no bait-feeding for photography, maintained distances, no off-road vehicle harassment).
• Engage on ESA enforcement: the 2008 listing remains contested in some jurisdictions; sustained support for the listing's continued application matters at the policy level.
• For shareholders of Arctic-operating fossil-fuel companies: shareholder engagement on Arctic exploration limits has been a meaningful mechanism for reducing planned industrial development in critical habitat areas.

Last verified: 2026-05-24 Conservation status: Vulnerable (IUCN Red List 2015 assessment); Threatened under U.S. ESA since 2008.

References

• IPCC (2021). Climate Change 2021: The Physical Science Basis (AR6 WGI). Chapter 9: Ocean, Cryosphere and Sea Level Change. Cambridge University Press.
• IUCN/SSC Polar Bear Specialist Group (2024). Subpopulation Status Assessments. https://www.iucn-pbsg.org/
• National Snow and Ice Data Center (NSIDC) (2024). Arctic Sea Ice News and Analysis. https://nsidc.org/arcticseaicenews/
• Stirling, I. (2011). Polar Bears: The Natural History of a Threatened Species. Fitzhenry & Whiteside.
• Stirling, I., Lunn, N. J., & Iacozza, J. (2011). Long-term trends in the population ecology of polar bears in western Hudson Bay in relation to climatic change. Arctic 64: 39–58.
• U.S. Fish and Wildlife Service (2008). Endangered and Threatened Wildlife and Plants; Determination of Threatened Status for the Polar Bear (Ursus maritimus) Throughout Its Range. 73 Federal Register 28212.
• Wiig, Ø., Amstrup, S., Atwood, T., et al. (2015). Ursus maritimus. IUCN Red List of Threatened Species. e.T22823A14871490.