Polar bears’ habitat is the sea ice that covers the Arctic Ocean; their primary habitat is annual sea ice over biologically productive waters (Stirling & Derocher 2012).
Figure 1: Polar bear (Ursus Maritimus) (Image courtesy of Mike Lockhart, USGS Volunteer)
Polar bears depend on sea ice as a platform for hunting seals. They require this platform for long enough each year to accumulate enough fat to survive periods of the year when seals are not available (typically the summer months) (Stirling & Derocher 2012).
Because of climate change, sea ice is rapidly melting. Scientists found that ice loss in the Antarctic is caused by ocean-driven melt and varying winds can cause transitions between relatively warm and cool ocean conditions (UW 2019). Human-induced climate change has caused long-term changes in the winds and because of this, warmer ocean conditions have become more prevalent. In model simulations of future winds, it was found that if greenhouse gas emissions continue to rise, winds will continue to shift in a way that increases the rate of ice loss (UW 2019).
With less time to access prey due to earlier ice breakage and later freezing, polar bears are forced into longer periods of fasting. A study done by Derocher & Sterling showed that polar bears also experience decreased access to denning areas, fewer and smaller cubs, and lower survival of cubs (Stirling & Derocher 2012). As the climate continues to warm, it is predicted that the Arctic may be ice-free as early as 2030 (Diebold et al 2023). It is also predicted that the negative effects on polar bears will increase to the point where polar bears will disappear.
There are a few potential solutions for the polar bears. In the most northern areas, there is thick multiyear ice where little light penetrates through. As temperatures increase, this ice will be replaced with annual ice which facilitates greater productivity and may create a better habitat for polar bears (Stirling & Derocher 2012). Another possibility is if greenhouse gas emissions can be controlled, winds may remain in their current state and may prevent greater warming to the ice sheets, however, this solution is more of a long shot.
References:
Diebold F, Rudebusch G, Gobel M, Coulombe P, Zhang B (2023) When will Arctic sea ice disappear? Projections of area, extent, thickness, and volume. Elsevier, https://doi.org/10.1016/j.jeconom.2023.105479
Stirling I, Derocher A (2012). Effects of climate warming on polar bears: a review of the evidence. Global Change Biology, https://doi.org/10.1111/j.1365-2486.2012.02753.x
UW News Staff. 2019 First evidence of human-caused climate change melting the West Antarctic Ice Sheet. https://www.washington.edu/news/2019/08/12/first-evidence-of-human-caused-climate-change-melting-the-west-antarctic-ice-sheet/ (date last accessed 2 February 2024).