考满分 toefl

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

听一段环境科学课的讲座。

1 .Last week, we looked at the factors that lead to cloud formation and rainfall. Despite extensive research, some aspects of rainfall are still poorly understood. For example, one thing that's been observed but has been hard to explain is that deforestation, clearing a forest of its trees, seems to lead to a decline in rainfall. Why would this be?

上周，我们探讨了导致云层形成和降雨的因素。尽管进行了大量研究，但降雨的一些方面仍然不太为人所理解。例如，有一个现象已被观察到，但很难解释：森林砍伐，也就是砍伐森林中的树木，似乎会导致降雨量下降。这是为什么呢？

1 .Well, let's review a few things. The moisture in the atmosphere is always going through a process called recycling. In the process of recycling, water from earth's surface evaporates into a vapor, the vapor in the air, then condenses into water, and this water then falls back to the region again as rain.

嗯，咱们回顾一些知识。大气中的水分一直在经历一个叫做 “水分循环” 的过程。在这个过程中，地球表面的水蒸发变成水汽，空气中的水汽随后凝结成水，这些水再以降雨的形式落回地面。

1 .Recycling can occur either over the ocean or over land. The evaporation of water from the ocean produces lots and lots of water vapor. You get this very moist air. On land, you have the evaporation of moisture from plants and trees. Plants and trees don't produce as much moisture as the ocean does. But still, since recycling is occurring, you can start to get a sense of how plants factor into land based rainfall.

水分循环可以在海洋上空或陆地上空发生。海洋中的水蒸发会产生大量水汽，形成非常湿润的空气。在陆地上，植物和树木中的水分也会蒸发。虽然植物和树木产生的水汽没有海洋那么多，但由于存在水分循环，大家就能大致理解植物在陆地降雨中起到了什么作用。

1 .Now, conventional models of rainfall, explanations of how much and where rain will fall. These models are centered around recycling. But these models aren't great at explaining certain aspects of land based rainfall, especially when it comes to rain forests that stretch into the interior of continents, areas like the Amazon rainforest, which reaches from the eastern coast of South America into the interior of the continent.

目前，传统的降雨模型，即解释降雨的多少和降雨区域的模型，主要围绕水分循环展开。但这些模型在解释某些陆地降雨情况时存在不足，尤其是对于延伸到大陆内部的雨林地区，比如从南美洲东海岸延伸到大陆内部的亚马逊雨林。

1 .You'd expect the forests inland areas to be relatively dry because they are far from that really moist ocean air. According to conventional models, the recycling of moisture from plants and trees in such rainforests simply could not by itself, provide enough water to maintain rainforest conditions in these interior regions.

按照常理，内陆地区的雨林应该相对干燥，因为它们远离海洋的湿润空气。根据传统模型，这些雨林中植物和树木的水分循环，无法单独为内陆地区的雨林环境提供足够的水分。

1 .So, clearly, something's missing from the models, something that explains where this additional moisture is coming from. And a newly proposed model does just that, by taking into consideration, air pressure. The researchers who came up with this model posit that what's been missing from the calculation all along is what happens when water vapor in the air, which is moisture in its gas form.

所以，显然这些模型遗漏了一些东西，这些东西能够解释额外的水分来自哪里。一个新提出的模型考虑到了气压因素，弥补了这一不足。提出这个模型的研究人员认为，一直以来在计算中被忽略的是，水汽，也就是气态的水分，在冷却并凝结成雨时会发生什么。

1 .When this vapor cools and condenses into rain, because as this water vapor rises into the higher cooler levels of the atmosphere, as it condenses into water, its volume decreases. In other words, the water vapor that used to take up space in its gas form, then takes up much, less space in its liquid form as rain water. This decrease in volume leads to a decrease in air pressure. So water vapor rises. It condenses into water. Volume decreases, and so air pressure decreases.

当水汽上升到大气中较冷的高层时，它会凝结成水，其体积会减小。换句话说，以气态形式占据一定空间的水汽，变成液态雨水后占据的空间要小得多。体积的减小会导致气压降低。所以水汽上升、凝结成水，体积减小，气压也随之降低。

1 .Now, air currents near earth's surface always flow toward areas of low pressure. So, when you have places where lots of evaporation and condensation are occurring, like rain forests, you get low pressure and lots of air currents being pulled in. Because the Amazon rainforest starts at the coast. Much of the air it's pulling in is moist air that originates over the ocean. This moisture eventually condenses and falls, then evaporates again. And then it's poured further inland by other low pressure areas, even deeper in the forest. This process happens many times, and the moisture that originated over the ocean travels far inland. As long as the forest cover is continuous.

而地球表面附近的气流总是流向低压区域。所以，在像雨林这样有大量蒸发和凝结现象发生的地方，就会形成低气压，吸引大量气流涌入。由于亚马逊雨林始于海岸边，它吸引的大部分气流都是来自海洋的湿润空气。这些水汽最终会凝结并降雨，然后再次蒸发。接着，其他低压区域会将这些水汽进一步推向内陆，深入雨林内部。这个过程会反复发生，来自海洋的水汽就能深入内陆。只要森林植被是连续的，这种情况就会持续。

1 .Now, this new model of rainfall does have its limitations. For example, it doesn't take into consideration variables like land formations. And when it comes to talking about the effects of land formations on weather patterns, well, I don't have to tell you it makes a big difference whether you're talking about flat land or mountainous land. But still, it's a model that can help us make informed decisions about forest conservation.

不过，这个新的降雨模型也有其局限性。例如，它没有考虑到地形等变量。说到地形对天气模式的影响，大家肯定知道，平坦地形和山地地形对天气的影响差别很大。但即便如此，这个模型能帮助我们在森林保护方面做出明智的决策。

1 .Forest cover has to be continuous in order for moist air to be pulled from the coastal parts of a rainforest into its far away interior parts. So it could be risky to clear trees in certain crucial areas. For example, clearing near the ocean could sever the flow of moist air currents that rain forests depend on, and could cause areas of forest in the interior of a continent to dry out.

为了让湿润空气从雨林的沿海地区流入内陆深处，森林覆盖必须保持连续。所以在某些关键区域砍伐树木可能存在风险。比如，在靠近海洋的地方砍伐树木，可能会切断雨林赖以生存的湿润气流，导致大陆内部的雨林地区干涸。