Part I
Pro: So since we're on the topic of global climate change and its effects, in Alaska, in the northern Arctic part of Alaska, over the last...thirty years or so, temperatures have increased about half a degree Celsius per decade, and scientists have noticed that there’s been a change in surface vegetation during this time. Shrubs are increasing in the "tundra".
Tundra is flat land with very little vegetation. Just a few species of plants grow there because the temperature is very cold, and there's not much precipitation. And because of the cold temperatures, the tundra has two layers: top layer, which is called the active layer, is frozen in the winter and spring, but thaws in the summer. Beneath this active layer is a second layer called "permafrost", which is frozen all year around, and is impermeable to water.
那里只有没几种植物生长，因为那里温度很低，而且降水也少。
1. arctic|ˈɑ:ktɪk|
adj. related to or happening in the regions around the North Pole 北极的；北极地区的
E.g.: This ship was designed expressly for exploring the Arctic waters.
这艘船是为考察北极水域而特意设计的。
antarctic |ænˈtɑ:ktɪk|
adj. related to or happening in the regions around the South Pole 南极的；南极地区的
E.g.: Antarctic air brought biting cold to southern Chile on Thursday.
周四，南极气流给智利南部带来了刺骨的严寒。
2. Celsius|ˈselsiəs|
adj. of or using a scale of temperature in which water freezes at 0˚ and boils at 100˚ 摄氏的
E.g.: It will be a mild night, around nine degrees Celsius.
晚间天气温和，温度约九摄氏度。
Fahrenheit|ˈfærənhaɪt|
adj. of or using a scale of temperature in which water freezes at 32˚ and boils at 212˚ 华氏温度计的，华氏的（冰点为32度，沸点为212度）
E.g.: By mid-morning, the temperature was already above 100 degrees Fahrenheit.
到早上10点钟，温度已经超过100华氏度了。
3. shrub |ʃrʌb|
noun. a large plant that is smaller than a tree and that has several stems of wood coming from the ground 灌木
E.g.: There is a small evergreen shrub on the hillside.
山腰上有一小块常绿灌木丛。
4. tundra |ˈtʌndrə|
noun. the large flat Arctic regions of northern Europe, Asia and N America where no trees grow and where the soil below the surface of the ground is always frozen 冻原，苔原（树木不生，底土常年冰冻的北极地区）
E.g.: There is a large amount of methane gas under the Siberian tundra.
西伯利亚的冻土地带之下有大量的甲烷气体。
5. precipitation|prɪˌsɪpɪˈteɪʃn|
noun. rain, snow, etc. that falls; the amount of this that falls 降水，降水量（包括雨、雪、冰等）
E.g.: Heavy vegetation may intercept a large amount of precipitation on its leaves.
浓密的植被的叶子中能截留大量的降水。
6. thaw|θɔ:|
verb. to turn back into water after being frozen （结冰后）解冻，融化，融解
E.g.: It's so cold the snow doesn't get a chance to thaw.
天太冷了，雪根本化不了。
7. permafrost|ˈpɜ:rməfrɔ:st|
noun. a layer of soil that is permanently frozen, in very cold regions of the world （寒带）永冻土层；永冻层
E.g.: As the permafrost melts, the land loses its capacity to absorb water.
由于冻土融化, 陆地会失去吸水性。
8. impermeable|ɪmˈpɜ:miəbl|
adj. not allowing a liquid or gas to pass through 不可渗透的；不透气的；不透水的
E.g.: The canoe is made from an impermeable wood.
独木舟由防水木头制成。
Part II
Stu: So because of the permafrost, none of the plants that grow there can have deep roots, can they?
Pro: No, and that's one of the reasons that shrubs survive in the Arctic. Shrubs are little bushes. They're not tall and being low to the ground protects them from the cold and wind. And their roots don't grow very deep, so the permafrost doesn't interfere with their growth. OK? Now since the temperatures have been increasing in Arctic Alaska, the growth of shrubs has increased. And this has presented climate scientists with a puzzle...
Stu: I'm sorry, when you say the growth of shrubs has increased, do you mean that the shrubs are bigger, or that there are more shrubs?
Pro: Good question! And the answer is both. The size of the shrubs has increased and shrub cover has spread to what was previously shrub-free tundra. Ok, so what's the puzzle? Warmer temperatures should lead to increased vegetation growth, right? Well, the connection is not so simple.
那么谜题是什么呢？温度升高应该会导致植被生长增加，对吧？但它们的关联其实并不是那么简单。
1. interfere with
to prevent sth from succeeding or from being done or happening as planned 妨碍；干扰
E.g.: She never allows her personal feelings to interfere with her work.
她从不让她的个人感情妨碍工作。
2. present |ˈpreznt|
verb. if something presents a difficulty, challenge, or opportunity, it causes it or provides it 引起；导致；带来；提供
E.g.: This presents a problem for many financial consumers.
这给很多金融消费者带来了一个问题。
3.cover |ˈkʌvə(r)|
noun. trees and plants that grow on an area of land （生长在一个地区的）树木植物，自然植被
E.g.: The total forest cover of the earth is decreasing.
地球上森林覆盖的总面积正在减少。
Part III
The temperature increase has occurred during the winter and spring, not during the summer. But the increase in shrubs has occurred in the summer. So how can increase temperatures in the winter and spring result in increased shrub growth in the summer? Well, it may be biological processes that occur in the soil in the winter, that cause increased shrub growth in the summer, and here's how: there are "microbes", microscopic organisms that live in the soil.
These microbes enable the soil to have more nitrogen, which plants need to live and they remain quite active during the winter. There're two reasons for this: first, they live in the active layer, which, remember, contains water that doesn't penetrate the permafrost.
Second, most of the precipitation in the Arctic is in the form of snow. And the snow, which blankets the ground in the winter, actually has an insulating effect on the soil beneath it. And it allows the temperature of the soil to remain warm enough for microbes to remain active. So there's been increased nutrient production in the winter. And that's what's responsible for the growth of shrubs in the summer and their spread to new areas of the tundra. Areas with more new nutrients are the areas with the largest increase in shrubs.
这可能是因为冬季土壤中发生的生物过程导致了夏季灌木生长增加，原因是：有“微生物”，生活在土壤中的微小生物。
1. microscopic |ˌmaɪkrəˈskɒpɪk|
adj. small and difficult or impossible to see without a microscope 极小的；微小的；需用显微镜观察的
E.g.: A plant's lungs are the microscopic pores in its leaves.
植物的肺就是其叶片上微细的气孔。
2. nitrogen 氮, oxygen 氧, hydrogen 氢, ammonia 氨, chlorine 氯
3. penetrate |ˈpenɪtreɪt|
verb. to go into or through sth 穿过；进入
E.g.: These fine particles penetrate deep into the lungs.
这些微小的尘埃可深深地吸入肺部。
4. blanket|ˈblæŋkɪt|
verb. to cover sth completely with a thick layer 以厚层覆盖
E.g.: Snow soon blanketed the frozen ground.
冻土上很快就形成了一层厚厚的积雪。
5. insulating |ˈɪnsəleɪtɪŋ|
adj. preventing heat, sound, electricity, etc. from passing through 起隔热（或隔音、绝缘）作用的
E.g.: One method of reducing heat loss is to wrap the baby in an insulating material.
减少热量损失的方法之一是用绝热材料来包裹婴儿。
6. responsible |rɪˈspɒnsəbl|
adj. being the cause of sth 作为原因；成为起因
E.g.: Cigarette smoking is responsible for about 90% of deaths from lung cancer.
因患肺癌而死亡者，约90%是吸烟所致。
Part IV
Stu: But, what about run-off in the spring, when the snow finally melts? Won't the nutrients get washed away? Spring thaw always washes away soil, doesn't it?
Pro: Well, much of the soil is usually still frozen during peak run-off. And the nutrients are deep down in the active layer anyway, not high up near the surface, which is the part of the active layer most affected by run-off. But as I was about to say, there's more to the story. The tundra is windy, and the snow is blown across the tundra, it's caught by shrubs. And deep snow drifts often form around shrubs.
And we've already mentioned the insulating effect of snow. So that extra warmth means even more microbial activity, which means even more food for the shrubs, which means even more shrubs and more snow around etc.. It's a circle, a loop. And because of this loop, which is promoted by warmer temperatures in winter and spring, well, it looks like the tundra may be turning into shrub land.
而且营养物质也只是在活跃层的深处，而不是在靠近地表的高处，靠近地表处也是活跃层中受径流影响最大的部分。
1. run-off
noun. rain, water or other liquid that runs off land into streams and rivers 径流，溢流（指流入河流中的雨水）
E.g.: The sewers collected sewage and storm run-off and discharged it, untreated, into the harbour.
污水和暴雨径流汇入下水道后被直接排入海港。
2. peak |pi:k|
adj. used to describe the highest level of sth, or a time when the greatest number of people are doing sth or using sth 最高度的；高峰时期的；巅峰状态的
E.g.: The athletes are all in peak condition.
所有运动员都处在巅峰状态。
3. drift|drɪft|
noun. a large pile of sth, especially snow, made by the wind 吹聚物；雪堆
E.g.: The road was blocked by deep drifts of snow.
道路被风吹来的厚厚积雪阻塞。
4. loop |lu:p|
noun. a shape like a curve or circle made by a line curving right round and crossing itself 环形；环状物；圆圈
E.g.: The road went in a huge loop around the lake.
那条路环湖绕了一个大圈。
5. promote |prəˈməʊt|
verb. to help sth to happen or develop 促进；推动
E.g.: a campaign to promote awareness of environmental issues
提高环保意识的运动
Part V
Stu: But will it be long-term? I mean maybe the shrubs will be abundant for a few years, and then it'll change back to tundra.
Pro: Well, shrub expansion has occurred in other environments, like semiarid grassland, and tall grass prairies. And shrub expansion in these environments does seem to persist, almost to the point of causing a shift. Once is established, shrub land thrives, particularly in the Arctic, because Arctic shrubs are good at taking advantage of increased nutrients in the soil, better than other Arctic plants.
这些环境中的灌木扩张似乎确实持续存在，几乎到了引起改变的地步。
1. semi-arid
adj. dry; with little rain 半干旱的
E.g.: arid and semi-arid deserts
干旱和半干旱的沙漠
2. prairie |ˈpreri|
noun. a flat wide area of land in N America and Canada, without many trees and originally covered with grass （北美的）大草原
E.g.: A single spark can start a prairie fire.
星星之火,可以燎原。
3. persist|pəˈsɪst|
verb. to continue to exist 维持；保持；持续存在
E.g.: If the symptoms persist, consult your doctor.
如果症状持续不消除，就得去看医生。
4. shift|ʃɪft|
noun. a change in position or direction 改变；转移；转换；变换
E.g.: a shift of emphasis
重点的转移
5. thrive|θraɪv|
verb. to become, and continue to be, successful, strong, healthy, etc. 兴旺发达；繁荣；蓬勃发展；旺盛；茁壮成长
E.g.: These animals rarely thrive in captivity.
这些动物栏养起来很少会肥壮。
