TPO9_Listening_1_3

climate

n. weather conditions; surrounding conditions

1. [U and C] the typical weather conditions in a particular area:

weather

v. expose to atmospheric conditions; become worn by exposure to the weather; overcome, atmosphere

n. layer of gases surrounding the earth; layer of gases surrounding a planet; climate of a particular region; unit of air pressure (Physics); tone or mood of a place or thing

 

area: a particular part of a country, town etc: in an area

2. a part of a house, office, garden etc that is used for a particular purpose:

 

region: 1. a large area of a country or of the world, usually without exact limits: = area

2. a particular part of someone's body: = area

 

district: 1. an area of a town or the countryside, especially one with particular features: rural/financial/theatre etc district
a house in a pleasant suburban district
2. an area of a country, city etc that has official borders:
a postal district

 

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

Lecturer: So since we're on the topic of global climate change and its effects, in Alaska, in the

northern Arctic Antarctica: the South pole ” part of Alaska, over the last thirty years or so, temperature has increased about

half a degree Celsius / Fahrenheit per decade, and scientists have noticed that there've been changes in

surface vegetation during this time. Shrubs are increasing in the "tundra".

 

tundra

n. vast and treeless arctic region (found for example in Siberia, northern Canada, and Lapland)

 

 

Shrub:. perennial plant which has woody stems and branches and ranges in height from very low to the size of a small tree, bush

 

Bush: n. perennial plant which has woody stems and branches and ranges in height from very low to the size of a small tree, shrub; wilderness, outback; tuft; minor league

 

 

Perennial :

Sedulous : persistent : perseverant:

Indeciduous

Deciduous adj. of passing interest; temporary and shed after period of time (of leaves, baby teeth, etc.)

 

Tundra is flat land withvery little vegetation. Just a few species( taxonomy ) of plants grow there because the temperature is very

cold, and there's not much precipitation 降雨量. 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(defrosted)解冻

in the summer. Beneath this active layer is the second layer called "permafrost" / permanent, which is frozen

all year around, and is impermeable / permeate / penetrate / to water.

 

Female Student: So because of the permafrost, none of the plants that grow there can have deep

roots, can they?

Lecturer: 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 in the ground protect 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 is presented to climate scientists

with a puzzle...

Male Student: I'm sorry, when you say the growth of shrubs has increased, do you mean the

shrubs are bigger, or that there are more shrubs?

IBT 新托福听力真题文本全收藏制作:先验理性(狗剩)

Lecturer: 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 connections are not so

simple. 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" 细菌/ bacteria / virus / microorganism , microscopic 精微的 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.

 

 

Nitrogen / phosphor   n. substance that produces light when subjected to radiation

n. colorless odorless gas, dominant element in the atmosphere, non-metallic element used in the production of fertilizers and explosives (Chemistry)

 

And the snow, which blankets the ground in the winter, actually has

an insulating(隔绝的)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 increase in 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.

Female student: But, what about run-off / escapein the spring, when the snow finally melts? Won't the

nutrients get washed away? Spring thaw always washes away soil, doesn't it?

Lecturer: 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(something which has accumulated due to the force of wind or water) often form around shrubs. And we've already mentioned the insulating effect of snow. So

that extra warmth means even more microbial 微生物的 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.

IBT 新托福听力真题文本全收藏制作:先验理性(狗剩)

Female student: 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.

Lecturer: Well, shrub expansion has occurred in other environments, like semiarid grassland, and

tall grass prairies(large open grassland, savanna, meadow). And shrub expansion in these environments does

seem to persist, almost to the point of causing a shift. Once is established, shrub land thrives Prosperity, thrift / thrives

particularly in the Arctic, because Arctic shrubs are good at taking advantage of increased

nutrients in the soil, better than other Arctic plants.

arrow
arrow
    全站熱搜

    bairdben 發表在 痞客邦 留言(0) 人氣()