Climate change is starving polar bears into extinction, according to research published Monday that predicts the apex carnivores could all but disappear within the span of a human lifetime. In some regions they are already caught in a vicious downward spiral, with shrinking sea ice cutting short the time bears have for hunting seals, scientists reported in Nature Climate Change.

Their dwindling body weight undermines their chances of surviving Arctic winters without food, the scientists added.

“The bears face an ever longer fasting period before the ice refreezes and they can head back out to feed,” said Steven Amstrup, who conceived the study and is chief scientist of Polar Bears International.

On current trends, the study concluded, polar bears in 12 of 13 subpopulations analyzed will have been decimated within 80 years by the galloping pace of change in the Arctic, which is warming three times as fast as the planet as a whole.

“By 2100, recruitment” — new births — “will be severely compromised or impossible everywhere except perhaps in the Queen Elizabeth Island subpopulation,” in Canada’s Arctic Archipelago, said Amstrup.

That scenario foresees Earth’s average surface temperature rising 3.3 degrees Celsius above the preindustrial benchmark. One degree of warming so far has triggered a crescendo of heatwaves, droughts and superstorms made more destructive by rising seas.

But even if humanity were able to cap global warming at 2.4 degrees Celsius — about half-a-degree above Paris Agreement targets, but hugely ambitious all the same — it would probably only delay the polar bears’ collapse.

The threat is not rising temperatures per se but the top-of-the-food-chain predators’ inability to adapt to a rapidly shifting environment.

Half of Earth’s land-based megafauna are classified as threatened with extinction, but only polar bears are endangered primarily by climate change.

But that status may not be unique for long, and should be seen as a harbinger of how climate will impact other animals in the coming decades, the authors warned.

Words to Learn 相关词汇

【巨型动物】 jùxíng dòngwù megafauna animals of particularly large size

【前兆】qiánzhào harbinger a person or thing that announces or signals the approach of another

周一发布的一项研究称，气候变化正在饿死北极熊并迫使它们灭绝。该研究预测，北极熊这一食物链顶端的食肉动物可能会在百年内几近灭绝。科学家在《自然气候变化》上发表的报告称，在部分地区，由于海冰消融缩短了北极熊捕食海豹的时间，北极熊已经陷入数量螺旋式下降的恶性循环。

科学家补充道，因为体重不断下降，北极熊在没有食物的情况下熬过北极冬天的几率降低了。

该研究的提出者、北极熊国际协会的首席科学家斯蒂芬▪阿姆斯特拉普说：“在冰雪重新冻结、可以外出觅食前，北极熊面临着前所未有的超长禁食期。”

该研究得出结论称，按照目前的趋势，随着北极加速变暖，研究分析的13个北极熊亚种群将有12个在80年内灭绝。目前北极变暖速度是地球整体的三倍。

阿姆斯特拉普称，“到2100年，新生北极熊数量将会剧减甚至降为零，除了（加拿大北极群岛的）伊丽莎白女王群岛的亚种群之外”。

科学家预测，到那时地球的平均表面温度将比工业化前基准水平高出3.3摄氏度。变暖1度迄今为止已经引发日益严重的热浪、干旱和超级风暴，而海平面上升使得风暴更具破坏力。

但即使人类可以将全球变暖控制在2.4摄氏度以内 —— 比巴黎协定目标大约高出0.5度，但也是极为雄心勃勃的计划 —— 这也很可能只会将北极熊灭绝的时间往后推迟一点。

威胁不是来自气温升高本身，而是源自北极熊无法适应快速变化的环境。

地球上有一半的陆地巨型动物被归类为濒危物种，但只有北极熊主要是因为气候变化而濒临灭绝。

研究报告的作者们警告称，但是北极熊也许不会长期独自处于这种境地，而应被视为预示着未来数十年气候将如何影响其他动物的一个先例。

(chinadaily.com.cn)