Global Change
AP Environmental Science Topic 9 8:14 English narration · English + 中文 subtitles burned in
Chapters
Transcript
In nineteen eighty-five, scientists studying the sky above Antarctica found something frightening: a hole in the ozone layer, the thin shield that keeps the sun's most dangerous rays off us.
1985年，研究南极上空天空的科学家发现了一件可怕的事：臭氧层出现了一个空洞。 臭氧层是一层薄薄的屏障，把太阳最危险的射线挡在我们之外。
Two years later, every country on Earth had signed a treaty banning the chemicals that caused it.
两年后，地球上每一个国家都签署了一项条约，禁止使用造成空洞的化学品。
Today the hole is slowly closing.
今天，这个空洞正在慢慢闭合。
That is the one global environmental problem the world has already fixed.
这是全世界已经解决的那一个全球环境问题。
This unit is about the rest.
这个单元讲的是其余的问题。
Unit Nine, in six steps.
第九单元，分六步。
First, ozone depletion.
第一，臭氧层破坏。
Then the greenhouse effect.
然后是温室效应。
Then climate change.
然后是气候变化。
Then a warming, souring ocean.
然后是变暖、变酸的海洋。
Then invasive and endangered species.
然后是入侵物种和濒危物种。
And last, the six threats pushing life off the planet.
最后是把生命逼出地球的六大威胁。
So what tore it open — what causes stratospheric ozone depletion?
那么是什么把它撕开的？
Chlorofluorocarbons — CFCs — were once used in fridges, air conditioners and spray cans.
氯氟烃，也就是CFCs，曾经用在冰箱、空调和喷雾罐里。
They drift slowly up into the stratosphere.
它们慢慢飘升到平流层。
There, ultraviolet light knocks a chlorine atom loose.
在那里，紫外线把一个氯原子打了下来。
That atom splits an ozone molecule apart, then comes back out unchanged, ready to do it again: a catalyst.
这个氯原子把一个臭氧分子拆开，然后又原样出来，准备再做一次：这就是催化剂。
One chlorine atom destroys about one hundred thousand ozone molecules.
一个氯原子能破坏大约十万个臭氧分子。
Thinner ozone lets more ultraviolet light reach the ground: more skin cancer and more eye cataracts in people, and damaged crops on farms.
臭氧变薄，就有更多紫外线到达地面：人会得更多皮肤癌和白内障，农田的作物也会受损。
Nature helps too — ice crystals above Antarctica speed the loss up each spring.
自然也在推波助澜——南极上空的冰晶让每年春天的损耗加快。
Reducing ozone depletion started in nineteen eighty-seven: the Montreal Protocol phased out CFCs worldwide, and it is working.
解决办法出现在1987年。 《蒙特利尔议定书》在全球淘汰了CFCs，而且确实有效。
But the replacements, the HFCs, trap heat.
但它的替代品氢氟烃却会吸热。
Now the second problem, and it is a different one.
现在来看第二个问题，它是一个不同的问题。
Sunlight passes through the atmosphere and warms the ground.
阳光穿过大气层，把地面晒热。
The warm ground sends energy back up as infrared — heat we cannot see.
变热的地面又把能量以红外线的形式送回去——那是我们看不见的热。
Greenhouse gases absorb some of that heat and send part of it back down.
温室气体吸收其中一部分热，再把一部分送回地面。
That is the greenhouse effect.
这就是温室效应。
It is natural, and we need it.
它是自然的，我们也需要它。
Which gases do this, and why are the greenhouse gases increasing?
是哪些气体在做这件事？
Carbon dioxide, methane, water vapour, nitrous oxide, and the CFCs again.
二氧化碳、甲烷、水蒸气、氧化亚氮，还有CFCs。
Water vapour is a greenhouse gas, but it does not drive climate change, because it stays in the air only days — a short residence time.
水蒸气确实是温室气体，但它并不推动气候变化，因为它在空气中只停留几天—— 停留时间很短。
The natural effect keeps the planet livable, near plus fifteen degrees instead of minus eighteen.
自然的温室效应让地球宜居，平均约为零上十五度，而不是零下十八度。
The problem is the enhanced version: extra gas, too much trapping.
问题在于被增强的那一部分：多出来的气体，困住了太多热量。
To compare gases fairly we use global warming potential, G W P.
为了公平地比较各种气体，我们使用全球变暖潜能值。
Carbon dioxide is the reference, with a G W P of one, so every other gas is measured against it.
二氧化碳是参照物， 所以它的数值是一。
Measured that way, CFCs are the strongest, then nitrous oxide, then methane.
按这个标准，CFCs最强，其次是氧化亚氮，再次是甲烷。
So why is carbon dioxide still the main problem?
那为什么二氧化碳仍然是主要问题呢？
Because potency is only half the story.
因为强度只是故事的一半。
We release far more carbon dioxide than anything else, from fossil fuels and clearing forests.
我们排放的二氧化碳远远多于其他任何气体，来自化石燃料和砍伐森林。
Strength times quantity decides the warming.
强度乘以数量，才决定了变暖的程度。
Add all that extra gas, and the climate itself shifts.
把这些多出来的气体加进去，气候本身就会改变。
Watch your words here: weather is one day, climate is decades.
这里要注意用词： 天气是一天，气候是几十年。
Ice cores let us read carbon dioxide and temperature far back through geological time, and the recent rise is fast.
冰芯让我们读出很久以前的二氧化碳和温度， 而最近的上升非常快。
The effects are already here — higher temperatures, melting sea ice and permafrost, rising seas, fiercer extremes.
影响已经出现了——平均气温升高，海冰和永久冻土融化， 海平面上升，极端天气更猛烈。
And one region is changing fastest.
而有一个地区变化得最快。
The poles are warming fastest, and here is why.
两极变暖最快，原因就在这里。
Bright ice reflects almost all the sunlight that lands on it — a high albedo.
明亮的冰几乎把落在它上面的阳光全部反射回去—— 反照率很高。
Dark ocean water reflects almost none, so it absorbs the energy instead.
深色的海水几乎不反射，反而把能量吸收进去。
Melt the ice, and dark water is uncovered; more energy is absorbed; the water warms; more ice melts.
冰一融化，深色的水就露出来；吸收的能量更多；水变暖；更多的冰融化。
The change feeds itself: a positive feedback loop.
这种变化会自我加强：这就是正反馈回路。
Thawing tundra adds to it by releasing methane.
融化的冻土释放甲烷，让它更严重。
The ocean takes the worst of it: it absorbs over ninety percent of the extra heat, and much of the extra carbon dioxide.
海洋承受了最重的一击：它吸收了超过九成的额外热量，还有很大一部分额外的二氧化碳。
The heat does two things.
这些热量做了两件事。
It makes seawater expand — thermal expansion — which raises sea level before any ice melts.
它让海水膨胀，在冰融化之前就已经抬高了海平面。
And it stresses corals until they push out the algae inside them and turn bone white — coral bleaching.
它还让珊瑚受到胁迫，直到珊瑚把体内的藻类排出去，变得惨白——这就是珊瑚白化。
Some recover; many die.
有些能恢复，很多会死去。
Now follow the carbon dioxide.
现在我们来追踪那些二氧化碳。
Carbon dioxide dissolves in seawater, and it does not just sit there.
二氧化碳溶解在海水里，而且不会就那样待着。
It reacts with water to make carbonic acid, which releases hydrogen ions.
它与水反应生成碳酸， 碳酸再释放出氢离子。
More hydrogen ions means a lower pH — ocean acidification.
氢离子越多，pH就越低——这就是海洋酸化。
Two things follow.
接着会发生两件事。
The extra hydrogen locks up carbonate, the building block of shells.
多出来的氢把碳酸根锁住，而碳酸根是贝壳的原料。
And the sourer water attacks calcium carbonate, so shells and coral skeletons grow thinner and dissolve.
变酸的水还会侵蚀碳酸钙，于是贝壳和珊瑚骨骼越来越薄，并开始溶解。
Warming is not the only pressure — the human impacts on biodiversity go wider.
变暖并不是唯一的压力。
An invasive species is a non-native species that spreads and harms its new home.
入侵物种是一种非本地物种，它扩散开来并伤害新的家园。
Most are tough generalists that breed fast, and with no natural predator there they outcompete the natives.
大多数是皮实的广适性物种，繁殖很快；在那里没有天敌， 于是它们在竞争中压过本地物种。
Trade and travel carry them everywhere.
贸易和旅行把它们带到各处。
Endangered species are the other side: a narrow diet, a small special habitat, or heavy hunting means lost first.
濒危物种是另一面：食性狭窄、生境狭小特殊，或者被大量猎捕，就最先消失。
Species that can adapt, or move, survive.
能适应、或者能迁移的物种才活得下来。
The exam bundles the human threats into one word: HIPPO.
考试把人类的威胁打包成一个词：HIPPO。
Habitat loss, the biggest of them all.
生境破坏，这是其中最大的一个。
Invasive species.
入侵物种。
Pollution.
污染。
Population growth.
人口增长。
And overharvesting.
还有过度开发。
Learn them in that order, worst first — some sources add a C for climate change, which we have just covered.
按这个顺序记，最严重的排在最前面—— 有些资料还会加一个C，代表气候变化，我们刚刚讲过。
Then read the last line, because that is the mark: no single threat explains what we are losing.
然后读最后一行，因为那才是得分点： 没有哪一个威胁能单独解释我们今天的损失。
It is the combination.
是它们的组合。
One threat deserves its own picture: habitat fragmentation.
有一个威胁值得单独画出来：栖息地破碎化。
A large, continuous habitat is cut into small, separated patches by roads, pipelines, farms and logging.
一大片连续的生境被道路、管线、农田和伐木切成一小块一小块、彼此分开的碎片。
The area lost looks small, but the harm is bigger than the area.
失去的面积看起来不大，但危害比面积更严重。
Small patches hold small populations that cannot reach each other, so genetic diversity falls.
小碎片里只有小种群，它们彼此无法往来，于是遗传多样性下降。
Every cut also adds edge, where predators and invaders get in.
每一道切口还增加了边缘，捕食者和入侵者就从那里进来。
The repair is a habitat corridor.
修复的办法是生境廊道。
Beyond corridors, conservation works in two places.
除了廊道，保护还在两个地方进行。
In-situ means in the wild: national parks, marine reserves, protected land.
就地保护是指在野外： 国家公园、海洋保护区、受保护的土地。
It saves the whole ecosystem, not one species.
它保住的是整个生态系统，而不只是一个物种。
Ex-situ means away from the wild: zoos, botanic gardens, seed banks, frozen zoos — the safety net when the habitat has gone.
迁地保护是指离开野外：动物园、植物园、种子库、冷冻动物园—— 当生境已经消失时，它就是安全网。
A full answer names both, then adds restoring habitat and sustainable land use.
完整的答案要说出这两个词， 再加上恢复生境和可持续的土地利用。
Let's finish with the number the exam loves.
最后来看考试最爱的那个数字。
Before industry, the air held about two hundred and eighty parts per million of carbon dioxide.
工业化之前，空气中大约含有百万分之二百八十的二氧化碳。
Today it is about four hundred and twenty.
今天大约是百万分之四百二十。
By what percentage has it risen?
它上升了百分之多少？
Pause here and try it.
先暂停，自己算一算。
First the change: four hundred and twenty minus two hundred and eighty is one hundred and forty.
先求变化量：四百二十减二百八十，等于一百四十。
Then divide the change by the original: one hundred and forty over two hundred and eighty is zero point five.
再用变化量除以原来的值：一百四十除以二百八十，等于零点五。
Times one hundred gives fifty percent.
乘以一百，就是百分之五十。
Always divide by the original.
永远要除以原来的值。
Five marks students throw away.
五个学生常丢的分。
One: ozone depletion and climate change are two different problems — never mix them.
第一，臭氧层破坏和气候变化是两个不同的问题——绝不要混在一起。
Two: give both halves of the greenhouse effect — short-wave sunlight in, long-wave infrared blocked going out.
第二，温室效应的两半都要说到——短波阳光进得来，长波红外出不去。
Three: name a feedback and say if it is positive or negative.
第三，说出是哪一种反馈，并说明它是正反馈还是负反馈。
Four: for acidification, say carbon dioxide plus water makes carbonic acid, which lowers pH.
第四，讲酸化时要说二氧化碳加水生成碳酸，使pH下降。
Five: spell out HIPPO, habitat loss first.
第五，把HIPPO逐个写出来，生境丧失放在最前面。