問題詳情

There are still a few people in northern Europe who think that global warming might not be such a badthing. In Britain, where summer can sometimes seem to last little more than a few weeks, many would welcomethe idea of it getting a bit hotter.Unfortunately, things are not so simple. Global warming doesn't just mean that the world will slowly getwarmer. Paradoxically, it could cause certain areas to get colder—a lot colder. The latest predictions are thatnorthern Europe could even be plunged into an ice age. While areas of southeastern Europe, such as Greece,would continue to get hotter and drier, Britain could find itself, in the winter months at least, surrounded by seaice.The reason for this concerns the Greenland ice sheet. This is one of the biggest expanses of ice in theworld—around 1,500 km long and 600 km wide. It is so big that if it all melted, sea levels would rise by 7 meters.Due to rising emissions of greenhouse gases, such as carbon dioxide from the combustion of fossil fuels, this icesheet is melting at an alarming rate. But how could the melting of the Greenland ice sheet threaten to plungenorthern Europe into a new ice age?The link in the chain of events is what some call the Gulf Stream and others call the Atlantic Conveyor.This is the stream of warm water that comes up from Central America and flows across the Atlantic to northernEurope. It is this huge mass of warm water which accounts for the relatively high temperatures enjoyed byBritain, for instance, compared with parts of Canada and Russia which are equally far north of the equator. Warmwater is conveyed across to Europe near the surface of the Atlantic, and, at its northernmost point, it cools andsinks because the water from the tropics has a higher salt content, making it denser and heavier than the waternear the arctic. The cold and dense water then flows south close to the ocean floor and back towards Central andSouth America to complete the cycle.Scientists are beginning to make bleak predictions of an impending ice age in the northern hemispherebecause they have observed that the water flowing from the melting Greenland ice sheet is flowing into the pathof the Gulf Stream. The water from the melted ice will reduce the density of the water in the Gulf Stream,stopping the water sinking in the north and thereby cutting off the deep southerly current, which, in turn, will cutoff the northerly flow of warmer water. At that point, the seas around Britain will begin to freeze.
76 What is the main purpose of the passage?
(A) to provide evidence for global warming
(B) to predict when the next ice age will begin
(C) to explain how global warming brings about an ice age
(D) to show how the density of the water in the Gulf Stream has changed over time

參考答案

答案：C
難度：非常簡單1
統計：A(0),B(0),C(2),D(0),E(0)

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