Wednesday, Jan 08, 2025 22:30 [IST]
Last Update: Tuesday, Jan 07, 2025 16:54 [IST]
The image of a polar bear stranded on melting sea ice is used nowadays as a symbol of the world’s rapidly changing climate. The consensus is clear, as Arctic sea ice melts, polar bears are finding it harder to hunt, mate and breed. While polar bears have shown some ability to adapt to changes in their surroundings for example, by foraging for food on land, or swimming more to hunt for prey. Scientists are in opinion that as sea ice diminishes, polar bears will find it harder to survive and populations will decline. Polar bears depend on sea ice for most important aspects of their lives including hunting, mating and resting. While polar bears are strong swimmers, capable of swimming for hours on end, they find swimming much more energy intensive than walking. As such, sea ice is crucial for polar bears to survive.
However, temperatures in the Arctic sea are rising nearly four times as fast as the global average and Arctic sea ice extent has declined since 1979 for every month of the year. According to Prof. Andrew Derocher who is an expert researcher in polar bear ecology and conservation at the University of Alberta, USA said “without sea ice, there is no sea ice ecosystem and losing that ecosystem includes losing polar bears”. Scientists have defined 19 key regions where polar bears live, extending across Arctic regions of Canada, Greenland, Norway, Russian and the US. All 19 subpopulations of polar bears have experienced some degree of ice loss. Few key regions are found to be as:
Seasonal: The “rich environment” allows bears to gain weight in spring. But in summer, the ice melts completely so polar bears are forced ashore and largely live off their fat reserves until ice reforms.
Divergent: This region has historically had ice coverage all year round. However, as the climate warms, the sea ice is retreating farther from shore. Convergent: In this region, ice collects along the shore in summer, allowing the bears to remain on sea ice all-year round. Archipelago: Full ice coverage all year round. This region is “likely to provide a last refuge for polar bears and their prey”.
However, in regions such as the Kane Basin, which is part of the “archipelago” group, a shift from thick, multi-year ice to thinner, seasonal ice has proved beneficial for bears. ??Historically, there was actually too much sea ice in the high Arctic for bears. The multi-year sea ice can be 10 metres thick, so it stifles productivity. So there is a transient phenomenon where in some of these high Arctic areas, as it’s getting warmer and sea ice is melting, the conditions are getting to be just right. According to Prof. Andrew Derocher "It is important to recognise that we fully expect this to be a transient phenomenon, given that climate change today is being driven by greenhouse gas emissions and that’s kind of a one way driver”. Polar bears most often feed on ringed seals that live at the ice edge, waiting for hours or even days for seals to emerge at breathing holes in the ice. Polar bear diets can also include bearded seals, harp seals and walruses. Polar bears get around two-thirds of their energy for the entire year in late spring and early summer, when prey is abundant. Then they are forced to do fasting throughout much of the autumn and winter when prey is scarce.
However, as the climate warms, sea ice is retreating earlier in spring and forming later in winter. This gives polar bears less time to hunt, forcing them to go without food for longer and swim greater distances. This extra exertion and lack of food can drive a decline in body condition and cause a drop in the average weight of adult bears. Meanwhile, fewer bear cubs survive and those that do are smaller.
Prof. Andrew Derocher and his group after investigation and research is in the opinion "With high greenhouse gas emissions, steeply declining reproduction and survival will jeopardize the persistence of all but a few high-Arctic subpopulations by 2100. Moderate emissions mitigation prolongs persistence but is unlikely to prevent some subpopulation extirpations within this century.”
The research study also identifies a fasting “threshold” for adult males, adult females and cubs. The authors estimate that cubs can survive around 117 days without food during this fasting period, while adult male and female polar bears can survive longer. They then explore expected sea-ice loss under different warming scenarios to determine when polar bears might start experiencing impacts from extended fasting. As the climate warms, polar bears are being forced to change their behaviour and their phenology, the timing of seasonal biological events, such as denning and breeding is shifting.
For example, research shows that as polar bears lose access to their typical diet of seals, they are becoming increasingly reliant on other types of food, including whale carcasses, sea duck eggs and reindeer.
Prof. Derocher says that as polar bears are being forced to spend more time on land, they are more likely to be seen in human rubbish dumps as they “seek alternative foods”. He adds that this raises questions around “human-bear interactions”. For example, research finds that longer ice-free periods are linked to increasing conflict between humans and polar bears. Meanwhile, female bears in the European Arctic now have only one-third as much denning habitat available as in the 1980’s. Unusually warm weather in winter can cause the collapse of dens that females build to birth and protect their young. Research study finds that female polar bears give birth to smaller litters of cubs when there are longer summer ice-free periods. Research group of Prof. Derocher is in opinion that "Changes in the timing, distribution and thickness of sea ice and snow have been linked to phenological shifts and changes in distribution, denning, foraging behaviour and survival rates of polar bears. Less ice is also driving polar bears to travel over greater distances and swim more than previously both in offshore and in coastal areas, which can be particularly dangerous for young cubs.”
Every few years, the “International Union for the Conservation of Nature” (IUCN) publishes a “Red List” an overview of the conservation status of threatened animal and plant species. The latest assessment for polar bears, published in 2024, classifies them as “vulnerable”, meaning they are facing a high risk of extinction in the wild.
Prof. Charlotte Lindqvist an expert researcher of “Polar Beers & Climate change” at University of Buffalo, New York says “The data shows a significant decline in sea ice throughout the entire polar bear range over the last 35 years, and if this trend continues the future looks dire for the polar bear species.” He also added "The single most important factor to improve the long-term survival of polar bears is reducing greenhouse gas emissions and stabilizing Arctic sea ice.” As the Arctic ice melts, polar bears are affected by increased shipping activities and a rise in opportunities for oil and gas development. Denning is the most vulnerable time in a polar bear's life. In a warming Arctic, the survival of every cub is critically important. Some polar bears may suffer from malnutrition and in extreme cases they may face starvation. Researchers have found that the main cause of death for cubs is either lack of food or lack of fat on nursing mothers. Researchers found that the main threats for polar beers are: climate change, human-caused mortality, mineral and energy resource exploration and development, contaminants and pollution, shipping, tourism related activities, and diseases and parasites. Hunting has been the greatest known cause of polar bear mortality. Today, polar bears are hunted by native arctic populations primarily for food, clothing, handicrafts, and sale of skins. Polar beers life expectancy in the wild is 25 to 30 years, but in captivity several polar bears have lived to more than 35 years old which now appears very difficult.
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