难度：大学英语四级
Why we still have brutal cold snaps even as the planet warms to record levels
By Laura Paddison, CNN
4 minute read
Published 8:17 AM EST, Mon January 15, 2024
Heavy snow on January 12 in Sioux City, Iowa.
After a summer of record-breaking heat, vast swaths of the United States are now grappling with extreme cold as a brutal Arctic blast brings snow squalls, deadly ice and life-threatening wind chills.
在经历了创纪录的夏季高温之后，美国大片地区现在正遭遇极端严寒天气，一股残酷的北极寒流带来了暴风雪、致命的冰层和危及生命的寒风。
As unprecedented heat makes way for cold, it can provide fuel for climate-change deniers who point to freezing temperatures as evidence that global warming is overstated.
随着前所未有的高温让位于寒冷，它为气候变化否认者提供了论据，他们指出寒冷的气温证明全球变暖被夸大了。
But scientists are clear: cold extremes will still occur even as winters warm overall.
但科学家们很清楚：即使整个冬天变暖，寒冷的极端天气仍会发生。
Global heat records outpace cold records — 2023 was the hottest year on record by a huge margin. And even as the US struggles to cope with intense bursts of heavy snow now, over the long term, the human-caused climate crisis has led to an alarming trend of disappearing snow in the Northern Hemisphere.
全球高温记录超过了低温记录——2023 年是有记录以来最热的一年，差距很大。尽管美国现在正努力应对强降雪，但从长远来看，人类造成的气候危机导致北半球降雪减少的趋势令人担忧。
Some scientists say that climate change may even be playing a role in these icy blasts, as warming in the Arctic increases the likelihood that frigid, polar air can sweep southwards.
一些科学家表示，气候变化甚至可能在这些冰冷的寒流中发挥作用，因为北极变暖增加了寒冷的极地空气向南席卷的可能性。
A worker helps remove snow from Highmark Stadium in Orchard Park, New York, on January 14.
What explains the cold?
Our weather is heavily influenced by the jet stream, a wavy river of fast-moving air high in the atmosphere.
我们的天气受高空急流的影响很大，高空急流是一股快速移动的空气流，在大气中呈波浪状。
When the jet stream swings south, it can push cold Arctic air into North America, Europe and Asia. When it retreats north, warm air will also push further north. A big high-pressure swing over Europe last January led to record warm winter temperatures.
当急流向南摆动时，它会将寒冷的北极空气推入北美、欧洲和亚洲。当它向北撤退时，温暖的空气也会向北推进。去年 1 月，欧洲上空出现了一次大型高压摆动，导致冬季气温创纪录地升高。
There’s also another factor to consider: the polar vortex, a belt of strong winds which sits extremely high in the stratosphere – above the level of the jet stream – around the North Pole.
还有另一个因素需要考虑：极地漩涡，这是一条环绕北极的强风带，位于平流层的极高处——在急流之上。
The polar vortex is like a spinning top. In its normal state it rotates very fast, keeping blisteringly cold air locked in the Arctic region. But it can get disrupted and knocked off course, becoming stretched and distorted, spilling out cold air and influencing the path of the jet stream.
极地漩涡就像一个旋转的陀螺。在正常状态下，它旋转速度非常快，将极寒的空气锁定在北极地区。但它可能会受到干扰并偏离轨道，变得拉伸和扭曲，溢出冷空气并影响急流的路径。
How the polar vortex can affect the weather
极地漩涡如何影响天气
The Arctic polar vortex is a belt of strong winds encircling very cold air, which sits high in the stratosphere over the North Pole. Usually the polar vortex is stable, keeping the cold air contained. But when it’s disrupted, it becomes less stable and expands, pushing cold air south. This influences the path of the jet stream, which sits lower in the atmosphere and is responsible for our weather.
北极极地漩涡是环绕着冷空气的强风带，位于北极上空的平流层高处。通常，极地漩涡是稳定的，将冷空气封闭在其中。但是，当它受到干扰时，它会变得不太稳定并扩大，将冷空气推向南方。这会影响位于大气较低处的急流的路径，而急流负责影响我们的天气。
It happened in 2021, bringing fierce cold to Texas, leading to nearly 250 deaths and knocking out power to large parts of the state.
这件事发生在 2021 年，给德克萨斯州带来了严寒，导致近 250 人死亡，并使该州大部分地区断电。
This is where the link to climate change comes in. Some scientists believe polar vortex disruptions and changes to the jet stream are being driven by warming in the Arctic, which is heating up around four times faster than the rest of the planet.
这就是与气候变化的联系所在。一些科学家认为，北极变暖导致极地漩涡的破坏和急流的变化，北极的变暖速度是地球其他地区的四倍左右。
The idea has been gaining traction since a 2012 paper by Jennifer Francis, a senior scientist at the Woodwell Climate Research Center in Massachusetts. It found that as the Arctic warms, the difference between the cold temperatures in the north and warm temperatures in the south is leading to a weaker, wavier jet stream, which pushes very cold air southwards.
自马萨诸塞州伍德威尔气候研究中心的资深科学家詹妮弗·弗朗西斯 (Jennifer Francis) 于 2012 年发表一篇论文以来，这一观点越来越受到关注。该论文发现，随着北极变暖，北方寒冷温度和南方温暖温度之间的差异导致急流减弱、波动，将极冷的空气推向南方。
Her much-debated paper kicked off more research into this developing area of science.
她备受争议的论文引发了对这一新兴科学领域的更多研究。
In 2021, Judah Cohen, a climatologist at Massachusetts Institute of Technology, published research which found rapid heating in parts of the Arctic, combined with high snowfall in Siberia, was making the jet stream more wavy and knocked the polar vortex off course.
2021 年，麻省理工学院的气候学家朱达·科恩 (Judah Cohen) 发表了一项研究，发现北极部分地区的快速升温，加上西伯利亚的大雪，使急流更加波动，并使极地漩涡偏离轨道。
“We are not arguing that winters are getting colder overall,” Cohen told CNN last year. But the idea that climate change will mean fewer swings between extreme temperatures is “an oversimplification,” he said.
科恩去年告诉 CNN：“我们并不是说冬天总体上会变得更冷。”但他表示，气候变化意味着极端温度之间的波动减少的想法是“过于简化”。
The area of science remains very unsettled, however, and others have said the links between Arctic warming and cold snaps are far from clear.
然而，这一科学领域仍然非常不稳定，其他人表示，北极变暖与寒流之间的联系还远不清楚。
While there have been a number of very cold Northern Hemisphere winters coinciding with warm Arctic winters, the difficulty is unpicking cause from effect, said James Screen, professor in climate science at Exeter University, whose own research concluded Arctic warming is not a trigger for colder winters.
埃克塞特大学气候科学教授詹姆斯·斯克林 (James Screen) 表示，虽然北半球有许多非常寒冷的冬季与温暖的北极冬季同时发生，但困难在于将原因与影响分开。他自己的研究得出的结论是，北极变暖并不是导致冬季变冷的触发因素。
Extreme cold snaps can be explained by normal climate variability, said Screen. In other words, even as winters get warmer, cold extremes will still occur.
斯克林说，极端寒流可以用正常的气候变化来解释。换句话说，即使冬天变暖，寒冷的极端情况仍会发生。
And climate change can also influence the severity of winter storms, as a warmer atmosphere can hold more moisture leading to more intense rain or snow when it falls.
而且，气候变化也会影响冬季风暴的严重程度，因为温暖的大气可以容纳更多的水分，从而导致降雨或降雪更强烈。
As scientists work to unravel complex links between climate change and periods of intense cold, all agree on one thing: the trend is for warmer winters.
当科学家们努力解开气候变化与严寒时期之间复杂的联系时，他们都同意一件事：冬季变暖的趋势。
“If you look at the data, we see that over the long term, global warming is leading to fewer and less severe cold extremes,” Screen said.
斯克林说：“如果你查看数据，我们会发现从长远来看，全球变暖导致寒冷极端天气减少和减轻。”
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