why do polar bears need ice caps
Polar bears are losing life-sustaining sea ice crucial for hunting, resting and breeding in all 19 regions of the
they inhabit, a study warned on Wednesday. As climate change pushes up Arctic temperatures, ice is melting earlier in spring and refreezing later in autumn, a team of researchers reported in the Cryosphere, a journal of the European Geosciences Union. Satellite data revealed that the total number of ice-covered days across the 19 regions declined at a rate of seven to 19 days per decade from 1979 to 2014, the researchers said. БTheir dependence on sea ice means that climate warming poses the single most important threat to (polar bearsБ) persistence,Б wrote the team. The global population of polar bears ( Ursus maritimus) is estimated at about 25,000, said the study. The bears, which have become emblematic of the ravages of global warming, spend most of their time on sheets of frozen ocean water, which melt and recede in warmer months, and then reform in winter. When the ice melts, the animals come ashore and survive on stored fat until it refreezes - a period that for some has become longer and longer. Scientists say the Arctic is warming at nearly double the global rate as a result of climate change fuelled by mankindБs burning of fossil fuels, a process that emits heat-trapping greenhouse gases. With longer iceless periods, polar bears have to swim further and further to find solid ground. Last year, the International Union for the Conservation of Nature (IUCN) said the creatures could see their numbers dwindle by nearly a third by mid-century. Their status on the IUCNБs red list of endangered species is currently listed as БvulnerableБ. The bears need sea ice for hunting as they cannot outswim seals, their preferred prey. They get around this by waiting near holes in the ice and ambushing the seals as they come up for air.
Male and female bears also meet on ice sheets to mate. БChanges in sea ice have been shown to impact polar bear abundance, productivity, body condition, and distribution,Б said the study. According to environmental group WWF, the retreating sea ice is more frequently bringing polar bears into confrontation with humans who live on land. With more water to navigate, Arctic shipping activities have increased, as well as opportunities for oil and gas development, further threatening the animalsБ habitat. Experts say Arctic sea ice melt will in turn contribute to sea level rise, and feed back into global warming - ice reflects warming sunlight away, while water absorbs the heat. This limited solar energy makes for cold temperatures and very little precipitation (either rain or snow) all year round, which helps maintain the polar ice caps. Polar ice caps and glaciers hold more than three-quarters of the Earth's freshwater and provide feeding and resting platforms for polar bears, seals, and marine birds. The melting of the polar ice caps is caused by the overall increase in global temperature, and this melting can have serious consequences for all organisms on Earth. Besides being important for marine life, ice caps help regulate sea level and global temperatures. Imagine that you have a cup of water and you place a large rock in the middle; the water is the ocean and the rock is a continent. If you place an ice cube on top of the rock, eventually it will melt into the 'ocean' around the rock, forcing water higher up around it. The same thing happens when polar ice caps melt. They melt directly into the ocean, increasing the volume of water and forcing seas higher onto land. Not only does the melting of the ice caps increase the volume of water in the oceans, it also decreases the salinity, or salt content.
Polar ice caps are made of fresh water, so adding more fresh water without adding more salt makes the ocean water less saline. This can cause problems for organisms that are well adapted to the very salty ocean waters. It is very important that the polar ice caps are frozen because the snow they are covered with reflects a large amount of light back into space that would otherwise increase the overall temperature of Earth. So you can see this is a serious problem. The polar ice caps help keep Earth a nice temperature, but the melting of polar ice caps increases the rate of global warming. Maintaining the Earth's temperature is very important to all the organisms that live in or around the polar ice caps. Despite being frozen and mostly covered with snow or ice, many small plants, invertebrates, and animals depend on the polar ice caps for food and shelter. Without the polar ice caps, many of these species would go extinct because they are well adapted to the climate and resources in these regions. Polar ice cap melting also affects those who are very far from the polar regions. Without the ice caps, the middle United States would be several degrees warmer in the winter, preventing an annual freeze necessary for wheat growing. People in sub-polar regions are already being affected because fish, walruses, and seals are changing their migration patterns, which makes it difficult to hunt them. Some seasonal variation occurs at the poles each year as the area of polar ice cover increases in the winter and decreases in the summer. However, the changes have been more significant in recent years. Summer decreases are hitting record lows, and the amount of accumulation in the winter is decreasing.
The thickness of the ice caps is also changing. As the ice caps melt, they not only cover less area but also become thinner. Usually, the core of the ice cap is what stays frozen all year long because it is so thick. But as it becomes thinner, the core of the ice cap may not be able to stay frozen during summer months, creating a domino effect of melting. The continued warming of Earth threatens the polar ice caps. These changes are becoming more rapid and may not be reversible. Understanding the causes and monitoring these changes are the first steps to slowing the melting of polar ice caps. However, we may not understand the full effects of melting polar ice caps until it's too late. Let's review. A polar ice cap is a region of land at the North or South Pole of a planet that is covered with ice. Polar ice caps and glaciers hold more than 3/4 of the Earth's freshwater and provide feeding and resting platforms for polar bears, seals, and marine birds. The melting of the polar ice caps is caused by the overall increase in global temperature, and this melting can have serious consequences for all organisms on Earth. As the polar ice caps melt, sea levels rise and the oceans become less saline. And the fact that the polar ice caps are frozen helps maintain even temperatures all over Earth, as well as a survivable environment for the organisms that live around the ice caps. Some seasonal variation occurs at the poles each year as the area of polar ice cover increases in the winter and decreases in the summer. However, the changes have been more significant in recent years. Understanding the causes and monitoring these changes are the first steps to slowing the melting of the polar ice caps. After the lesson, you should have the knowledge to:
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