Narrator: Listen to part of a lecture in an environmental science class.

旁白：听一段环境科学的课程。

Professor: I’d like to take you back about 11 thousand years ago when Earth entered the latest interglacial period.

教授：这节课我将带你们回到一万一千年前，当时，地球进入了最近的一次间冰期。

Interglacial periods are, typically periods of time between Ice Ages, when the climate warms, and the glacial ice retreats for a time, before things cool off again and another Ice Age begins.

所谓间冰期，指的是两次冰河世纪的之间的时间段，这时气候暖和，冰川暂时消退，直到气候重新变冷，另一个冰河世纪开始，间冰期结束。

And for over the past several million years, Earth’s sort of default climate has actually been Ice Age, but we have experienced periodic regular thaws, and the last one, the one we are in now, started about 11 thousand years ago.

在过去的几百万年里，地球的主要气候特征实际上是冰河纪，但实际上它也有规律地解冻，而上一次解冻也就是我们现在所处的这次间冰期，就始于一万一千年前。

Now, the typical pattern for an interglacial period, and we have studied several, is that the concentration of carbon dioxide and methane gas actually reaches it... its peak, that is, there is the most carbon dioxide and methane gas, uh, greenhouse gases in the atmosphere just after the beginning of the interglacial period.

我们之前学习过的间冰期的几种典型模式，其中一种是大气中二氧化碳和甲烷含量达到峰值，即在间冰期的开端，大气中的温室气体（二氧化碳和甲烷）已经积累至其上限值。

And then, for reasons which are not entirely clear, the concentration of greenhouse gases gradually goes down.

之后，因为一些现在还不是特别明确的原因，温室气体的聚集逐渐下降。

Now, the climate continues to warm for a while because there is a lag effect.

由于滞后效应，气候还会持续变暖一段时间。

But uh, gradually as the concentration of greenhouse gases goes down, Earth starts to cool again, and eventually you slip back into an Ice Age.

但是随着温室气体浓度的下降，地球会再次变冷，最终回到冰河时代。

Um, however, for the latest interglacial period, the one we are in now, this pattern did not hold, that is, the concentration of carbon dioxide and methane dipped a little bit after, uh, uh, after peaking at the beginning, near the beginning of the interglacial period, but then it began to rise again.

嗯，但是，在最后一次间冰期之后，即我们现在所处的时代里，这种模式就不适应了，虽然在进入间冰期之后，甲烷和二氧化碳的含量自达到峰值以后有所下降，但之后它又开始上升了。

Um ... What was different about this interglacial period than the other ones?

嗯，这一次间冰期和之前的间冰期，有什么不同呢？

Well, one of the big differences is human activity.

这次间冰期和之前的相比，最重要的不同，在于人类的活动。

People began to raise crops and animals for food instead of hunting for them.

人类种植庄稼，圈养牲畜来获取食物，而不是猎取它们。

This is the agricultural revolution.

这是农业的重大革命。

And it began to happen in the earliest stages about 11 thousand years ago.

而且，这项革命发生在一万一千年前的早期。

Now, scientists have tended to regard ... the ... uh ... agricultural revolution as a beneficiary of the ... uh ... fortuitous shift in climate.

现在，科学家们都倾向于认为农业革命是……嗯……受益于偶然性的气候变化的。

However, some new theories of climate, new theorists of climate have proposed that perhaps humanity was having an effect on the climate as far back as the beginnings of the agricultural revolution.

但是，一些新的气候理论学家提出了许多新的气候学理论，提出，自从此次间冰期的开始后的农业革命开始，人类的活动一直都在影响自然气候。

When you grow crops and uh, pasture your animals, one of the things you do is you cut down the forests.

当我们种植农作物，放牧牲畜时要做的第一件事情就是砍伐森林。

If you cut down the forests, when you burn the trees for fuel and don’t replace them with other trees, or when you just leave them to rot and don’t allow other trees to grow, you end up with a lot more carbon in the form of carbon dioxide getting into the atmosphere.

当森林被伐之后，人类就把木头作为燃料，并且没有换植其它的植株或者我们把砍得的木头烂在地里让别的植物没法生长，这样的结果是，很多碳元素会以二氧化碳的形式存在，并进入大气层。

Um ... another gas associated with the spread of agriculture is methane.

另一种随着农业扩张而过量产生的其它气体是甲烷。

Methane forms in large concentration above wetlands, and as it turns out, the cultivation of certain grains creates vast areas of artificial wetlands, and probably drastically increases the amount of methane getting into the atmosphere, over and above what would be there.

甲烷在湿地上大批形成，而且，随着谷物种植面积的扩大，一大批人造湿地被制造出来，大量增加了进入大气层的甲烷含量，超过了以往的应有的水平。

So, um... agriculture, the ... the spread of agriculture, you know we are talking over thousands of years, um... but this could very well had a profound effect on the composition of Earth’s atmosphere.

总之，嗯……农业的扩张，我们这里谈论的是成千上万年的农业扩展史，但是这段时间内的农业扩张对地球大气层的成分有着非常深远的影响。

It’s kind of ironic to think that absent that effect, it maybe that we would be heading into an Ice Age again.

如果不是因为这种温室效应，也许我们会再次进入冰河时代，这着实让人觉得讽刺。

In fact, back in the 1970s, a lot of theorists were predicting that, you know, the climate would start to cool and we’d slowly enter into the new Ice Age.

实际上，回溯到1970年代，许多环境理论专家就预测过气候的再次变冷，世界再次重新进入冰河世纪。

And then they were puzzled as to why it didn’t seem to be happening.

之后，他们被事实弄得很困惑：为什么地球还没有变冷？

Umm... now, what are the implications for the future?

嗯，现在，气候变化对我们的未来意味着什么呢？

Well, um... it is a little tricky.

嗯……这其实非常的微妙。

I mean, you could say, well, here is an example of ... um ... human activity, the agricultural revolution which actually was beneficial, we altered the climate for the better, perhaps, by preventing an Ice Age.

我的意思是，你可以说，这里有一个例子，人类活动，例如农业革命实际上是有益的，因为我们也许通过阻止冰河时代，把气候变好了。

But then industrialization, of course, has drastically increased the amount of carbon dioxide that humans are putting into the atmosphere, the burning of fossil fuels tends to put a lot of CO2 into the atmosphere.

但是，其后的工业革命，大大增加了人类向空气中注入二氧化碳的总量，化石燃料的消耗往大气中灌注了海量的二氧化碳。

Um... so we are entering into uncharted territory now, in terms of the amount of carbon dioxide, the concentrations of carbon dioxide that are now being put into the atmosphere as a result of industrialization and the use of fossil fuels.

就二氧化碳的含量而言，我们现在进入了一片未知的领域，工业革命和化石燃料大量消耗，使得大气层的二氧化碳含量高度聚集。