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每年的2月27日是国际北极熊日，于2011年由北极熊国际协会提倡设立，旨在提醒全社会关注北极熊和它们的栖息地北极。这群可爱的“大白”们其实是最怕热的熊，目前的处境并不太好。随着全球气候变暖，北极地区的海冰面积正大幅萎缩，这对北极熊的生存构成了严重威胁。
Polar bears fur is not white. The fur is actually transparent.
北极熊的皮毛不是白色，事实上是透明的。
It consists of two layers of transparent hair, a soft thick undercoat and a layer of hollow guard hairs.
它有两层透明皮毛，一层是柔软厚实的皮毛，另一层是中空的护毛。
The layers only appear white because the air spaces in each hair scatter all visible wavelengths of light.
我们之所以看到的是白色，是因为北极熊毛发中空部分对光线的折射造成的。
Underneath this fur polar bears have black skin.
在这层毛皮下，皮肤是黑色的。
Sunlight can penetrate the bears transparent fur and reach its black skin, which absorbs the suns heat and warms the bears body.
阳光可以穿过透明的皮毛，到达黑色的皮肤，吸引太阳的热量，为北极熊起到保暖作用。
Polar bears are excellent swimmers.
北极熊是非常出色的游泳健将。
Theyve evolved to have a narrow skull and a long flexible neck, which are believed to help streamline their bodies in the water and provide the reach and flexibility they need to bring their noses up for air.
他们狭窄的头骨和长而灵活的脖子都有利于它在水中流线型运动，也可帮助它们抬起鼻子以增加其伸展范围和灵活性。
Their front paws are large up to 12 inches wide, flat and act as paddles as the bears swim and even hunt marine animals while underwater.
它们的前爪扁而平，宽度达12英寸，可充当桨，甚至可以助它在水下捕食。
Additionally, the bears have a two-to-four-inch layer of fat that helps keep them buoyant and warm as they swim.
此外，北极熊还有一层2到4英寸厚的脂肪，可帮助在游水时保持浮力和温暖。
Polar bears are the largest land carnivore.
北极熊是最大的陆地食肉动物。
They may grow up to eight feet tall and weigh over one thousand seven hundred and sixty pounds, far outweighing the next largest land predator — the kodiak brown bear by several hundreds of pounds.
它们身高可达7英尺，体重可超1760磅，远超第二陆地捕食者的科迪亚克棕熊几百磅。
This hefty size allows polar bears to hunt large powerful animals like walruses and beluga whales.
庞大的体型可捕杀例如海象、白鲸类的力量型动物。
Because of their tremendous size, polar bears have no natural predators apart from humans.
也正是由于巨大的体型，除人类以外，北极熊没有任何天敌。
Polar bears only live in the Arctic.
北极熊只生活在北极地区。
This region includes areas of Russia, Greenland, Norway and the United States.
其中包括俄罗斯、格陵兰、挪威和美国。
However, up to 80 percent of the worlds polar bears live in one country —Canada.
然而，世界上超过八成的北极熊都生活在一个国家——加拿大。
Polar bears may traverse islands and coastlines.
它们有时会横跨岛屿和海岸线。
But most of the time the bears live directly on sea ice that can be found between land masses.
但大部分时候，北极熊会直接生活在陆地之间的冰面上。
However, as climate change is causing sea ice to recede, polar bears are beginning to make their way further inland to find food.
但是，由于全球气候变暖，冰层开始融化，北极熊开始长途跋涉来到内陆地区觅食。
Polar bears are not endangered... for now.
北极熊并没有濒临灭绝……只是到目前为止。
Between 22,000 and 31,000 polar bears are in the wild, but their populations may be at risk in the future.
现在野生北极熊数量有22000至31000只左右，但它们的种群可能处于危险之中。
Climate change and rising ocean temperatures are causing sea ice, the polar bears hunting grounds to melt more rapidly and for longer periods of time.
气候变化和海温上升导致冰层融化，北极熊捕食地点融化速度更快、持续时间更长。
This may play a role in a projected 30 percent population decrease by 2050. Life on top of the world comes with many challenges.
预计到2050年，北极熊数量会减少三成。它们在世界之巅的生活会引来许多挑战。
But with translucent fur, strong swimming capabilities, and considerable body size, polar bears have become well-adapted to life in the wintry north.
半透明的皮毛、出色的游水能力、巨大的体型，都让北极熊能够更适应极冷的北极圈地区。
