Rival theories for a global cooling
有关一次全球冷却事件的竞争理论
Did a cosmic impact cause the Younger Dryas cooling?
新仙女木降温事件是天体撞击导致的吗？
My latest Mind and Matter column for the Wall Street Journal:
Scientists, it’s said, behave more like lawyers than philosophers. They do not so much test their theories as prosecute their cases, seeking supportive evidence and ignoring data that do not fit-a failing known as confirmation bias. They then accuse their opponents of doing the same thing. This is what makes debates over nature and nurture, dietary fat and climate change so polarized.
我在《华尔街日报》Mind and Matter专栏的最新文章中说：
据说科学家表现得更像律师而不是哲学家。他们不像对待案件诉讼那样详细地检验他们的理论，他们寻找支撑证据并且忽略掉那些不合用的数据——这就是被称为确认偏误【校注：指个人选择性地回忆、搜集有利细节，忽略不利或矛盾的资讯，来支持自己已有的想法的片面诠释的现象。】的过失。接着他们指控他们的对手在做同样的事。就是这个原因，导致有关先天与后天、膳食脂肪和气候变化等问题上的争议变得如此两极化。
But just because the prosecutor is biased in favor of his case does not mean the defendant is innocent. Sometimes biased advocates are right. An example of this phenomenon is now being played out in geology over the controversial idea that a meteorite or comet hit the earth 12,900 years ago and cooled the climate.
但检察官对案件带有偏见，并不意味着被告人无辜。有时候带偏见地坚决拥护是对的。这种现象最近在地质学领域有了个例子，那就是关于12900年前陨石（或彗星）撞击地球导致气候变冷的争议。
That the climate suddenly cooled then, plunging the Northern Hemisphere back into an ice age for 1,300 years, is not in doubt. The episode is known as the Younger Dryas, because in Scandinavia abundant pollen from a tundra flower called the mountain avens, Dryas octopetala, reappears in soil from this date, indicating that the forest had once more given way to tundra. With the sudden arrival of cooler, drier and less predictable seasons, early human attempts at agriculture in the Near East ceased, and people returned to nomadic hunting and gathering.
气候在那时突然变冷，使北半球猛然回到冰河时期并持续长达1300年，这是毫无疑问的。这段插曲被称为新仙女木事件，因为在斯堪的纳维亚，大量来自苔原花朵仙女木的花粉，在这一时期的土壤中再次出现，意味着森林曾经又一次让位于苔原。因为更加寒冷干旱和更加难以预测的季节变化突然出现，人类在近东的早期农业尝试停止了，人们回到了游动性的捕猎采集生活。
The cause of this cold lurch was seemingly settled some time ago when Wallace Broecker, a Columbia University geochemist, suggested that a North American ice sheet collapsed, flooding the Atlantic with fresh water, which interrupted the normal circulation of the Gulf Stream.
早些时候，造成这次寒冷突变的原因看似已有了定论。哥伦比亚大学的地质化学家Wallace Broecker认为，因北美冰盖崩塌而新增的融水涌入大西洋，这使得墨西哥湾流的正常循环被打断。
Then a marine geologist, James Kennett of the University of California, Santa Barbara, said he had found evidence of the impact of a large object from space 12,900 years ago, in the form of carbon spherules in silt.
然而，加州大学圣芭芭拉分校的一位海洋地理学家James Kennett说，他从淤泥里碳球粒状体的形态中发现了12900年前大型天体撞击的证据。
Dr. Kennett’s argument is that a swarm of meteorites punched through the atmosphere and caused a vast conflagration, filling the air with dust and soot. This shut out the sun, causing decades of continuous winter -sufficient to trigger an advance of ice sheets that, even when the dust cleared, kept the climate cool for more than a thousand years, at least in the Northern Hemisphere.
Kennett博士的观点是，大量陨石击穿大气层并导致了大规模燃烧，使空气中充满了灰尘和烟雾。它们遮蔽了太阳，导致了持续数十年的冬天，从而引致冰盖大幅扩张。即使灰尘消散后，这些冰盖也足以使寒冷气候维持一千年以上，至少在北半球是这样。
Dr. Kennett prosecuted his case with gusto, also suggesting that the impact had extinguished North American mammoths, just as an earlier impact had finished off the dinosaurs (a theory hard to reconcile with the survival of mammoths for thousands of years longer on islands off Siberia and Alaska, where hunters could not reach them).
Kennett博士兴致盎然地提出了他的根据，还认为这次撞击导致了北美猛犸象的灭绝，就像之前的一次撞击导致了恐龙灭绝那样（不过这个理论很难和如下事实协调起来：猛犸象在猎人无法到达的西伯利亚和阿拉斯加边缘岛屿又生存了几千年）。
He suffered a key setback in recent years when several groups failed to find the right kinds of spherules or otherwise duplicate the results of his team’s work-and, worse, when a spherule sample from Younger Dryas rocks proved to be only 135 years old.
近年来他遭受的一个重要挫折是，几个小组都没能找到能印证该理论的其他球粒体，或者好歹和他的团队有同样的发现，并且更糟糕的是，一个新仙女木岩石中的球粒体样本被证明只有135年历史。
But spherules, dated to the right period, now have apparently shown up. Dr. Kennett and colleagues have published evidence in the prestigious Proceedings of the National Academy of Sciences that a “black mat” from the sediment of a Mexican lake dates to 12,900 years ago and shows a sudden peak of magnetic and carbon spherules, “nanodiamonds” of a kind known as lonsdaleite, and charcoal: all of it evidence of extreme heat.
但是如今，形成年代与该理论吻合的球粒体看来已经被找到了。Kennett博士和他的同事们在权威的《美国国家科学院院刊》(PNAS)上发表了证据，表明墨西哥湖沉积物中有一黑色薄层形成于12900年前，其中含有突然陡增的带磁性碳球粒体，一种被称为六方碳的“纳米钻石”，还有木炭：所有这些都是极端高温的证据。
Last year Michael Higgins of the University of Quebec published details of an underwater crater in the Gulf of St. Lawrence, arguing that it may also date from as little as 12,900 years ago. The crater, three miles across, has the characteristic central mound of a fresh meteorite impact. Its meteorite was probably too small to shift the climate, but perhaps it was part of a swarm.
去年，魁北克大学的Michael Higgins发表了关于圣劳伦斯湾一个水下陨石坑的细节，声称它也可以追溯到12900年前。这处3英里宽的陨石坑具有新陨石撞击坑所特有的中心土丘。这颗陨石可能太小，尚不足以影响气候，但也许它是一个陨石群的一部分。
After the previous debacles, the jury will take much convincing that the new results can be replicated. But the burden of proof has shifted a little in Dr. Kennett’s favor. After all, Dr. Broecker and his followers, too, may be emotionally invested in his ice-sheet theory: Confirmation bias can affect us all.
先前的论点垮台之后，要让陪审团相信新结果能够重复观察到，还需要花很多功夫。但举证责任现在向有利于Kennett博士的方向偏移了一点。毕竟，Broecker博士和他的追随者们也可能已经在他的冰盖理论上投入了情感：确认偏误可以影响我们所有人。
翻译：史祥莆（微博：@史祥莆）
校对：Marcel ZHANG（微博：@马赫塞勒张），小册子（微博：@昵称被抢的小册子）
编辑：辉格@whigzhou