万物简史 第620期:冰河时代(17)

What is most alarming is that we have no idea—none—what natural phenomena¹ could so swiftly rattle² Earth's thermometer. As Elizabeth Kolbert, writing in the New Yorker, has observed: "No known external force, or even any that has been hypothesized, seems capable of yanking the temperature back and forth³ as violently, and as often, as these cores have shown to be the case." There seems to be, she adds, "some vast and terrible feedback loop," probably involving the oceans and disruptions of the normal patterns of ocean circulation, but all this is a long way from being understood.

最令人不安的是，我们不知道——报本不知道——是什么自然现象使得地球的温度发生如此快速的变化。就像伊丽莎白·考柏特在《纽约客》上撰文所指出的那样：“没有已知的任何外部力量——甚至没有任何假设的外部力量——使得地球温度发生如冰核所显示的那样剧烈、那样经常的变化。这当中似乎存在一个，”她继续写道，“范围很广而又十分可怕的反馈循环。”这很可能和海洋及洋流的正常循环被打乱有关，但是要彻底了解这一切，我们还有很长一段路要走。

One theory is that the heavy inflow of meltwater to the seas at the beginning of the Younger Dryas reduced the saltiness (and thus density) of northern oceans, causing the Gulf⁴ Stream to swerve⁵ to the south, like a driver trying to avoid a collision. Deprived of the Gulf Stream's warmth, the northern latitudes⁶ returned to chilly⁷ conditions. But this doesn't begin to explain why a thousand years later when the Earth warmed once again the Gulf Stream didn't veer⁸ as before. Instead, we were given the period of unusual tranquility known as the Holocene, the time in which we live now.

有一种理论认为，在新仙女木初期，大量流人海洋的冰雪融水降低了北半球海水的盐分浓度（以及密度），使得墨西哥湾暖流折转向南，就像一个司机为了避免撞车而改变方向一样。由于缺少了墨西哥湾暖流所带来的热量，北半球纬度较高地区的气候重新回复到严寒的状况。但是这不能解释为什么1000年以后，当地球重新变暖时，墨西哥湾暖流却没有像以往那样转向。相反，我们进入了一个异常平稳的被称为全新世的时期，也就是我们现在所生活的时期。

There is no reason to suppose that this stretch of climatic stability should last much longer. In fact, some authorities believe that we are in for even worse than what went before. It is natural to suppose that global warming would act as a useful counterweight to the Earth's tendency to plunge⁹ back into glacial conditions. However, as Kolbert has pointed¹⁰ out, when you are confronted with a fluctuating and unpredictable climate "the last thing you'd want to do is conduct a vast unsupervised experiment on it." It has even been suggested, with more plausibility¹¹ than would at first seem evident, that an ice age might actually be induced by a rise in temperatures. The idea is that a slight warming would enhance evaporation¹² rates and increase cloud cover, leading in the higher latitudes to more persistent¹³ accumulations of snow. In fact, global warming could plausibly¹⁴, if paradoxically, lead to powerful localized cooling in North America and northern Europe.

没有理由认为这一段稳定的气候会持续很长时间。事实上，某些气象学方面的权威认为，我们的气候正在变得比以前更加糟糕。人们很自然地以为全球性的气候变暖会对地球重新回到冰川状态起一种阻碍作用。然而，正如考柏特所指出的那样，当你遇到不可预测的气候波动时，“你最不愿意做的事就是主动对它进行一种大范围的监测”。有人甚至认为，气温的上升很可能会促使冰川期的到来。这种观点乍一看上去似乎不大明白，实际上很有道理。气温稍稍上升会使蒸发速度加快，云层加厚，从而使得纬度较高地区的积雪持续不断地增加。事实上，全球气温的上升可能会使北美洲和欧洲北部局部地区变得更加寒冷。这是有道理的，虽然是矛盾的。

1 phenomena   

n.现象

参考例句：

• Ade couldn't relate the phenomena with any theory he knew.艾德无法用他所知道的任何理论来解释这种现象。
• The object of these experiments was to find the connection,if any,between the two phenomena.这些实验的目的就是探索这两种现象之间的联系，如果存在着任何联系的话。

2 rattle   

v.飞奔，碰响；激怒；n.碰撞声；拨浪鼓

参考例句：

• The baby only shook the rattle and laughed and crowed.孩子只是摇着拨浪鼓，笑着叫着。
• She could hear the rattle of the teacups.她听见茶具叮当响。

3 forth   

adv.向前；向外，往外

参考例句：

• The wind moved the trees gently back and forth.风吹得树轻轻地来回摇晃。
• He gave forth a series of works in rapid succession.他很快连续发表了一系列的作品。

4 gulf   

n.海湾；深渊，鸿沟；分歧，隔阂

参考例句：

• The gulf between the two leaders cannot be bridged.两位领导人之间的鸿沟难以跨越。
• There is a gulf between the two cities.这两座城市间有个海湾。

5 swerve   

v.突然转向，背离；n．转向，弯曲，背离

参考例句：

• Nothing will swerve him from his aims.什么也不能使他改变目标。
• Her car swerved off the road into a 6ft high brick wall.她的车突然转向冲出了马路，撞向6英尺高的一面砖墙。

6 latitudes   

纬度

参考例句：

• Latitudes are the lines that go from east to west. 纬线是从东到西的线。
• It was the brief Indian Summer of the high latitudes. 这是高纬度地方的那种短暂的晚秋。

7 chilly   

adj.凉快的，寒冷的

参考例句：

• I feel chilly without a coat.我由于没有穿大衣而感到凉飕飕的。
• I grew chilly when the fire went out.炉火熄灭后，寒气逼人。

8 veer   

vt.转向，顺时针转，改变；n.转向

参考例句：

• He is unlikely to veer from his boss's strongly held views.他不可能背离他老板的强硬立场。
• If you fall asleep while driving,you'll probably veer off the road.假如你开车时打瞌睡，可能会驶离道路。

9 plunge   

v.跳入，(使)投入，(使)陷入；猛冲

参考例句：

• Test pool's water temperature before you plunge in.在你跳入之前你应该测试水温。
• That would plunge them in the broil of the two countries.那将会使他们陷入这两国的争斗之中。

10 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

11 plausibility   

n. 似有道理, 能言善辩

参考例句：

• We can add further plausibility to the above argument. 我们可以在上述论据之外，再进一步增添一个合理的论据。
• Let us consider the charges she faces, and the legal plausibility of those charges. 让我们考虑一下她面临的指控以及这些指控在法律上的可信性。

12 evaporation   

n.蒸发，消失

参考例句：

• Be careful not to lose too much liquid by evaporation.小心不要因蒸发失去太多水分。
• Our bodies can sweat,thereby losing heat by evaporation.我们的身体能出汗，由此可以蒸发散热。

13 persistent   

adj.坚持不懈的，执意的；持续的

参考例句：

• Albert had a persistent headache that lasted for three days.艾伯特连续头痛了三天。
• She felt embarrassed by his persistent attentions.他不时地向她大献殷勤，使她很难为情。

14 plausibly   

似真地

参考例句：

• The case was presented very plausibly. 案情的申述似很可信。
• He argued very plausibly for its acceptance. 他为使之认可辩解得头头是道。