Climate change is a global concern that affects many species and ecosystems; polar bears are essentially the poster child for species impacted by Earth’s warming temperatures. “Earth’s 2015 surface temperatures were the warmest since modern record keeping began in 1880,” according to independent analyses by NASA and the National Oceanic and Atmospheric Administration. Polar bears depend on sea ice in the Arctic for all aspects of their life; global warming has caused a marked decrease in the polar ice.
In May of 2008, polar bears were listed as a threatened species in the United States under the Endangered Species Act; they are the first species to be listed as a direct result of climate change (World Wildlife Fund, 2016). Polar bears are physiologically designed to survive in bitterly cold temperatures, uniquely suited for a high fat diet of seals, and are for the most part solitary animals; loss of sea ice and higher temperatures due to global warming, as well as increased pollution are all cause for concern regarding the fate of the polar bear.
Scientifically named, Ursus maritimus, polar bears are classified as marine mammals and are the largest carnivorous mammal on Earth (Plataforma, 2015). Their name literally means “Sea Bear” (Colorado State University, 2014). Polar bear’s bodies are designed for cold water and even colder air temperatures. They have a thick layer of body fat, which can measure up to four and a half inches as well as a water repellent coat (Polar Bears International, 2016). Contrary to popular belief, polar bear fur is not actually white.
In actuality, they have black skin and each hair is transparent and pigment free with a hollow core that causes visible light to be reflected (Polar Bears International, 2016). Designed to conserve body heat, the bears have small ears and short, compact, tails in addition to their substantial fat layer. Due to these physical adaptations it is very easy for the bears to overheat; if temperatures continue rising as predicted, this could be detrimental to the species.
Unlike other bears, with the exception given only to pregnant females, polar bears do not hibernate and are active year round. It is estimated that polar bears can go for up to 220 days without food; unfortunately loss of sea ice and available prey has caused a longer fasting period resulting in reduce fat stores. Ultimately, this has lead to a decrease in the polar bear population and a reduction the cub survival rate. Polar bears consume the highest lipid diet of all species, which provides them with all of the nutrients they need (USGS, 2015, April 1).
Ringed seals are the preferred food source for polar bears because they have an extremely high fat content and are the most abundant seal in Arctic waters. Polar bears spend fifty percent of their time hunting seals, however only two percent of these hunts are successful (World Wildlife Fund, 2016). Ringed seals depend on solid ice and sea ice for resting and giving birth. When sea ice is reduced, the larger floes float further out to sea, forcing the bears into longer swims over unproductive waters to reach it.
Since the seals also use the ice, the bears will follow the floes, sometimes for hundreds of miles, in order to reach their food source. It has been noted that many bears are lost to drowning in these situations, especially females with cubs (Polar Bears International, 2016). Ice-free periods in the summer are becoming longer; without access to seals some polar bears turn to terrestrial food sources, which are unlikely to help them to survive (USGS, 2015, July 3). Berries, birds, and eggs are not sufficient in fat and calories to compensate for the loss of seals (USGS, 2015, April 1).
In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined,” Dr. Karyn Rode (USGS, 2015, April 1). It is predicted that as the Arctic continues to warm, nearly two-thirds of the polar bear population could vanish by the end of this century (Polar Bears International, 2016). Although climate change is the major cause of the vulnerability of the polar bear, it is not alone. Exposure to chemical contaminants is the third largest threat facing polar bears (Plataforma, 2015).
Chemicals that have been found include DDT, PCB, and brominated flame-retardants. Ocean currents carry these pollutants to the Arctic, where they make their way up the food chain; the Arctic has a high-fat food web and these chemicals are fat-soluble (Polar Bears International, 2016). These pesticides and organochlorine compounds affect the animal’s endocrine and reproductive systems, especially the thyroid hormones and deiodinase enzymes, which are responsible for stabilizing thyroid hormones in the tissues (Plataforma, 2015).
Certain toxins affect the nervous system, potentially altering cognitive skills, while others cause shrinking of the genitalia, weakening of the bones, and suppression of the immune system (Polar Bears International, 2016). As temperatures increase there is concern that new vectors for disease will begin to infiltrate new territory exposing the bears to pathogens they had not previously encountered and have no immunity against. Loss of sea ice forcing the bears inland opens up an entirely new set of issues including diseases and parasites, competition with land based bears like the grizzly, and increased human interaction.
Humans are to blame for most of the problems facing the bears, including global warming. Global temperature averages have increased by 0. 23 degrees Fahrenheit from 2014 to 2015. Most of the increase has occurred in the past thirty-five years, in fact, fifteen of the sixteen warmest years on record have happened since 2001 (NASA, 2016). Our planet is currently experiencing a long-term warming trend that is being exacerbated by human consumption of fossil fuels.
Researchers in the Arctic have taken ice core samples to measure levels of carbon dioxide over the past 10,000 years; their studies show that never before have carbon dioxide levels reached three hundred parts per million, while in the past thirty years the levels have significantly passed this mark (Endangered Polar Bear, 2013). This study shows the direct human contribution to climate change relating to greenhouse gas emissions from the burning of fossil fuels such as oil and coal.
We have compounded this problem by reducing the amount of carbon dioxide being absorbed from the atmosphere due to the deforestation in the tropical regions (Polar Bears International, 2016). Our planet is caught up in a positive feedback loop; warmer temperatures melt the ice so there is less reflection of solar energy, without the ice, the dark open water absorbs the solar energy, and the warmer temperatures thaw out permafrost, which then releases more greenhouse gases. Polar bears are amazing creatures that have evolved to survive in one of the most extreme biomes on our planet.
Their bodies are designed for extreme temperatures and their diet is ideally suited to supporting their needs. Unfortunately, unless we act soon to reduce greenhouse gas emissions and reverse global warming, those adaptations will be the very thing to cause the demise of the polar bear. Humans, on a global scale, need to begin the process of reversing our negative impact; it will take decades of mitigation to see results regarding the sea ice (USGS, 2015, July 3). If changes are not made in a timely manner, the only polar bears that our descendants may have the opportunity to see will be behind the glass at the zoo.
