評論
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Narrator:Listen to part of a lecture in an earth science class.
獨白:請聽下面一段地球科學課講座的一部分。
Professor:We're really just now beginning to understand how quickly drastic climate change can take place.
教授:我們剛剛了解激烈的氣候變化發生的有多快。
We can see past occurrences of climate change that took place over just a few hundred years.
我們看到過去幾百年前發生的氣候變化事件。
Take uh… the Sahara Desert in Northern Africa.
比如說，北非的撒哈拉大沙漠。
The Sahara was really different 6,000 years ago.
6000 年前的撒哈拉大沙漠可是截然不同，
I mean, you wouldn't call it a tropical paradise or anything,
我的意思是你不會稱它為“熱帶天堂”或什么的。
uh…or maybe you would if you think about how today in some parts of the Sahara it…
嗯，如果你想想在撒哈拉的有些地方今天是什么樣子你也可能會這么叫，
it only rains about once a century.
有些地方一個世紀才下一場雨。
Um… but basically, you had granary and you had water.
不過，基本上你還是有糧食和水的。
And what I find particularly interesting and amazing really, what really indicates how un desert-like the Sahara was thousands of years ago,
而且我覺得非常有趣及不可思議的是一些東西展現了撒哈拉在幾千年前是多么的不像沙漠，
was something painted on the rock, pre-historic art, hippopotamuses,
它們就是巖石上的繪畫，史前藝術，石頭上畫著的河馬，
cos you know hippos need a lot of water and hence? Hence what?
因為你們知道，河馬是需要大量的水才能生存，那么因此，因此什么呢？
Student:They need to live near a large source of water year round
學生:他們需要終年生活在一個巨大的水源附近。
Professor:That's right.
教授:是這樣的。
Student:But how is that proved that the Sahara used to be a lot wetter?
學生:但是那怎么證明撒哈拉過去非常潮濕？
I mean the people who painted those hippos, well, couldn't they have seen them on their travels?
我是說那些畫河馬的人，嗯，難道就不可能是他們在旅途中見到的嗎？
Professor:Okay, in principal they could, Karl.
教授:問的好，是有這種可能，卡爾。
But the rock paintings aren't the only evidence.
但是巖石繪畫不是唯一的證據。
Beneath the Sahara are huge aquifers, basically a sea of fresh water,
撒哈拉下面有巨大的蓄水層，一片淡水的海洋，
that's perhaps a million years old filtered through rock layers.
那可能是經過巖石層過濾的，已經有一百萬年歷史。
And…er…and then there is fossilized pollen, from low shrubs and grasses that once grew in the Sahara.
并且，嗯，有一些石化的花粉，來自于曾經生長在撒哈拉的小灌木叢和草叢。
In fact these plants still grow, er…but hundreds of miles away, in more vegetated areas.
實際上，這些植物現在仍然在生長，嗯，但是是在離這里幾百英里遠的更多植物生長的區域。
Anyway, it's this fossilized pollen along with the aquifers and the rock paintings,
不管怎么說，就是這些石化花粉和蓄水層，還有巖石上的畫作，
these three things are all evidence that the Sahara was once much greener than it is today,
這三樣東西證明撒哈拉曾經比現在有更多植物的證據，
that there were hippos and probably elephants and giraffes and so on.
可能不僅有河馬，還有大象和長頸鹿等等。
So what happened?
那么發生什么事兒了呢？
How did it happen?
是怎么發生的呢？
Now, we're so used to hearing about how human activities are affecting the climate, right?
現在，我們很習慣聽到人類活動是如何影響氣候的。
But that takes the focus away from the natural variations in the earth climate, like the Ice Age, right?
但是這卻將將注意力從地球氣候的自然變化轉移開了，比如說冰河世紀，對吧？
The planet was practically covered in ice just a few thousand years ago.
這個星球在幾千年前都是被冰雪覆蓋的，
Now as far as the Sahara goes, there is some recent literature that points to the migration of the monsoon in that area.
現在就撒哈拉沙漠而言，近期有些文學作品指向了那個地區季候風的遷移。
Students:Huh?
學生:啊？
Professor:What do I mean?
教授:我說的是什么意思呢？
Okay, a monsoon is a seasonal wind that can bring in a large amount of rainfall.
是這樣，季候風是指季節性的風，而這種風能夠帶來大量的雨水。
Now if the monsoon migrates, well, that means that the rains move to another area, right?
現在如果季候風遷移，也就意味著雨水也跟著去了另一個地區，對吧？
So what caused the monsoon to migrate?
那么是什么使得季候風遷移呢？
Well, the answer is:
嗯，答案就是:
the dynamics of earth's motions,
地球的運動動力學。
the same thing that caused the Ice Age by the way.
同樣這也是造成冰河世紀原因。
The earth's not always the same distance from the sun,
地球和太陽的距離并不總是一樣遠，
and it's not always tilting toward the sun at the same angle.
也不總是以同樣的角度對著太陽的。
There are slight variations in these two perimeters.
它們的周長有一點點變化。
They're gradual variations but their effects can be pretty abrupt.
而這種不顯著的變化使得其影響卻有可能很突然，
And can cause the climate to change in just a few hundred years.
可以引起氣候在短短幾百年間發生變化。
Student:That's abrupt?
學生:這稱得上突然？
Professor:Well, yeah, considering that other climate shifts take thousands of years, this one is pretty abrupt.
教授:嗯，你們想想啊，其他的氣候變化可是花了幾千年啊，這個已經是很突然了。
So these changes in the planet's motions, they called it “the climate change”, but it was also compounded.
所以這些星球運動中的變化，他們稱之為“氣候變化”，這也是混合的。
What the Sahara experienced was um…a sort of “runaway drying effect”.
撒哈拉沙漠所經歷的變化，嗯，是一種“逃離干燥效果”，
As I said the monsoon migrated itself, so there was less rain in the Sahara.
就像我說的季候風本身會遷移，所以撒哈拉沙漠的雨水變少，
The land started to get drier, which in turn caused huge decrease in the amount of vegetation,
土地開始變干燥，于是造成了植物的大量減少，
because vegetation doesn't grow as well in dry soil, right?
因為植物在干燥的土壤里無法很好的生長。
And then, less vegetation means the soil can't hold water as well, the soil loses its ability to retain water when it does rain.
后來，植物太少也導致了土壤無法保留住水分，土壤也失去了在下雨時保持住水分的能力。
So then you have less moisture to help clouds form, nothing to evaporate for cloud formation.
所以，后來濕度不夠也難以形成云層，因為沒有可以蒸發的能形成云層的東西。
And then the cycle continues, less rain, drier soil, less vegetation, fewer clouds, less rain etc. etc..
然后形成了這樣的循環，雨水少，土地變干燥，植物變少，云層減少，下雨就更少，如此循環往復。
Student:But, what about the people who made the rock paintings?
學生:但是，那些在巖石上繪畫的人呢？
Professor:Good question.
教授:這個問題提得好。
No one really knows.
沒有人真正知曉。
But there might be some connections to ancient Egypt.
但是也許與古埃及有點聯系，
At about the same time that the Sahara was becoming a desert…
與撒哈拉變成沙漠在同一時期。
Student:Uh-huh
學生:哦。
Professor:5,000 years ago, Egypt really began to flourish out in the Nile River valley.
教授:五千年前，埃及在尼羅河山谷真正開始興旺繁榮。
And that's not that far away.
那離得并不遠。
So it's only logical to hypothesize that a lot of these people migrated to the Nile valley when they realized that this was more than a temporary drought.
當很多人意識到這不僅僅是暫時性的干旱的時候，他們就遷移到了尼羅河山谷，這種假設也符合邏輯。
And some people take this a step further.
有些人對這點做了進一步的研究，
And that's okay, that's science and they hypothesize that this migration actually provided an important impetus in the development of ancient Egypt.
科學上假設這次的遷移實際上在古埃及的發展中提供了一個重要的動力。
Well, we'll stay tuned on that.
好的，我們會繼續研究的。
