北极熊将在21世纪灭绝？真实数据情况让人心痛不已

北极熊是当今世界上最大的陆地肉食动物，主要生活在北冰洋、北极圈附近，能够适应十分恶劣的生存环境。然而，北极熊在2008年便被认定为濒危物种，加上近年来温室效应加剧造成海冰不断消退，以及海洋污染等问题的日益严重，导致北极熊的生存区域缩小，觅食困难，面临严重的生存危机。不少科学家都认为北极熊很有可能在21世纪灭绝。
The polar bear is the world’s largest land carnivore, living mainly in the Arctic Ocean and near the Arctic Circle, and is able to adapt to very harsh living conditions. However, the polar bear was recognized as an endangered species in 2008, and the receding sea ice caused by the greenhouse effect in recent years, as well as the growing problems of marine pollution, have led to a reduction in the survival area of the polar bear, making it difficult to find food and facing a serious survival crisis. Many scientists believe that polar bears are likely to become extinct in the 21st century.

下面的数据可视化项目清晰地展现了目前北极熊种群地生存境况。一共有19个亚种群，分为4个等级：蓝色代表稳定，红色代表减少，绿色代表增加，白色代表缺乏数据。目前现存的北极熊数量约有22000至31000只，而19个亚种群中只有两个处于数量增长的状况。选中某个亚种群，如Davis Strait亚种群，可以看到标签中显示的预估数量约2150只。

上文提到，导致北极熊面临生存危机的直接原因是海冰的减少。下图中直接展现了从1979年到2020年海冰范围和海冰面积的变化。北冰洋的海冰范围由1230万平方千米缩减到1070万平方千米，而海冰面积由940万平方千米缩减到890万平方千米。
As mentioned above, the direct cause of the survival crisis for polar bears is the decline in sea ice. The changes in sea ice extent and sea ice area from 1979 to 2020 are shown directly in the figure below. The Arctic Ocean sea ice extent shrinks from 12.3 million square kilometers to 10.7 million square kilometers, while the sea ice area shrinks from 9.4 million square kilometers to 8.9 million square kilometers.

这一变化看似不大，但实际上海冰范围和面积在一年之中也有很大的变化。每年9月，北极海冰达到最小值。由于全球变暖，海冰在春季较早消退，秋季较晚形成。目前，9月的北极海冰正以每十年13.1%的速度下降。如此一来，每年的春季和秋季之间海冰范围和面积都会急剧减少，远低于图中显示的数据。
This change may seem small, but the actual extent and area of Shanghai ice also varies considerably throughout the year. Arctic sea ice reaches its minimum each September. Due to Global Warming, sea ice recedes earlier in the spring and forms later in the fall. September Arctic sea ice is now declining at a rate of 13.1% per decade. In this way, the extent and area of sea ice decreases dramatically between spring and fall each year, well below the data shown in the figure.

不只是北极熊，很多生活在北极地区的物种都正面临严重的生存危机。科学家预测，到2040年，当所有其他大面积的夏季冰层消失后，加拿大东北部和格陵兰岛北部将只剩下边缘的冰层。这个 "最后的冰区 "很可能成为北极熊和其他依赖冰的生命的重要区域。
Not just polar bears, but many species living in the Arctic are facing a serious existential crisis. By 2040, scientists predict that only a fringe of ice will remain in Northeast Canada and Northern Greenland when all other large areas of summer ice are gone. This "Last Ice Area " is likely to become important for polar bears and other life that depends on ice.

数据可视化项目网址：
https://public.tableau.com/zh-cn/gallery/changing-habitat-polar-bears?tab=viz-of-the-day&type=viz-of-the-day