首页
登录
职称英语
【31】 [br] 【34】 [originaltext] Lecturer: In the last lecture, we looked at the
【31】 [br] 【34】 [originaltext] Lecturer: In the last lecture, we looked at the
游客
2024-01-07
97
管理
问题
【31】 [br] 【34】
Lecturer: In the last lecture, we looked at the adverse effects of desert dust on global climate. Today we’re going to examine more closely what causes dust storms and what other effects they can have. As you know, dust storms have always been a feature of desert climates, but what we want to focus on today is the extent to which human activity is causing them. And it is this trend that I want to look at, because it has wide-ranging implications. So, what are these human activities? Well, there are two main types that affect the wind erosion process, and thus the frequency of dust storms. There are activities that break up naturally wind-resistant surfaces such as off-road vehicle use and construction and there are those that remove protective vegetation cover from soils, for example, mainly farming and drainage. In many cases the two effects occur simultaneously which adds to the problem.
Let’s look at some real examples and see what I’m talking about. Perhaps the best-known example of agricultural impact on desert dust is the creation of the USA’s ’dust bowl’ in the 1930s. The dramatic rise in the number of dust storms during the latter part of that decade was the result of farmers’ mismanaging their land. In fact, choking dust storms became so commonplace that the decade became known as the ’Dirty Thirties’.
Researchers observed a similar, but more prolonged, increase in dustiness in West Africa between the 1960s and the 1980s when the frequency of the storms rose to 80 a year and the dust was so thick that visibility was reduced to 1,000 metres. This was a hazard to pilots and road users. In places like Arizona, the most dangerous dust clouds are those generated by dry thunderstorms. Here, this type of storm is so common that the problem inspired officials to develop an alert system to warn people of oncoming thunderstorms. When this dust is deposited it causes all sorts of problems for machine operators. It can penetrate the smallest nooks and crannies and play havoc with the way things operate because most of the dust is made up of quartz which is very hard. Another example - the concentration of dust originating from the Sahara has risen steadily since the mid-1960s.
This increase in wind erosion has coincided with a prolonged drought, which has gripped the Sahara’s southern fringe. Drought is commonly associated with an increase in dust-raising activity but it’s actually caused by low rainfall which results in vegetation dying off.
One of the foremost examples of modern human-induced environmental degradation is the drying up of the Aral Sea in Central Asia. Its ecological demise dates from the 1950s when intensive irrigation began in the then Central Asian republics of the USSR. This produced a dramatic decline in the volume of water entering the sea from its two major tributaries. In 1960, the Aral Sea was the fourth-largest lake in the world, but since that time it has lost two-thirds of its volume, its surface area has halved and its water level has dropped by more than 216 metres. A knock-on effect of this ecological disaster has been the release of significant new sources of wind-blown material, as the water level has dropped.
And the problems don’t stop there. The salinity of the lake has increased so that it is now virtually the same as sea water. This means that the material that is blown from the dry bed of the Aral Sea is highly saline. Scientists believe it is adversely affecting crops around the sea because salts are toxic to plants.
This shows that dust storms have numerous consequences beyond their effects on climate, both for the workings of environmental systems and for people living in drylands ...
选项
答案
dry thunderstorms
解析
转载请注明原文地址:http://tihaiku.com/zcyy/3342232.html
相关试题推荐
Onthebeachtherewasacastofa______.[br]【20】[originaltext]Presente
Onthebeachtherewasacastofa______.[br]【18】[originaltext]Presente
Onthebeachtherewasacastofa______.[br]【17】______[originaltext]Pr
【31】[br]【40】[originaltext]Lecturer:Inthelastlecture,welookedatthe
【31】[br]【37】[originaltext]Lecturer:Inthelastlecture,welookedatthe
【31】[br]【36】[originaltext]Lecturer:Inthelastlecture,welookedatthe
【31】[br]【33】[originaltext]Lecturer:Inthelastlecture,welookedatthe
【31】[br]【32】[originaltext]Lecturer:Inthelastlecture,welookedatthe
【21】[br]【30】[originaltext]Tutor:Goodmorningeveryone.WellIthinkwecans
【21】[br]【29】[originaltext]Tutor:Goodmorningeveryone.WellIthinkwecans
随机试题
CompletetheapplicationformusingNOMORETHANTHREEWORDS.Applicationforpa
[originaltext]EducationexpertssayAfrica’sgrowinghighereducationsyste
患儿女,3岁。出生后胸部出现突起畸形。查体:胸骨体前凸,两侧的肋软骨和肋骨凹陷。
6岁患儿,3天前开始出现高热伴寒战,右膝部肿胀,右腿屈曲,拒绝主动活动,被高度怀
A.新药B.已有国家标准的药品C.国家基本药物D.处方药E.非处方药必须凭执业医
根据变电一次设备标准缺陷库,集合式电力电容器放电线圈漏油,漏油速度每滴时间3秒,
皮亚杰关于儿童道德发展阶段认为道德教育的目的就是使儿童达到道德的自律。() A
根据1974年联大通过的《关于侵略定义的决议》,下列选项中哪些属于侵略行为?(
下列关于子公司法人资格和民事责任承担的表述中,符合公司法律制度规定的是()。A
(2013年真题)根据《标准施工招标文件》,发包人的义务主要有()。A.提
最新回复
(
0
)