雅思考试主要是通过对考生听、说、读、写四个方面英语能力的考核,综合测评考生的英语沟通运用能力,实现“沟通为本”的考试理念。对于雅思考生来说,也有很多考试难点和政策盲区需要帮助解答。今天雅思无忧网小编准备了雅思听力part2真题 雅思听力里的略读(二),希望通过文章来解决雅思考生这方面的疑难问题,敬请关注。
雅思听力答案的正确写法,总是让许多考鸭都很烦恼。可以全大写吧?日期该怎么写?缩写简写得分吗?明明听到单数为什么答案是复数?赶紧对照下面的听力答案填写标准,改正自己的拼写习惯,不要最后明知道答案还因为写得不规范扣分!
2020雅思考试听力答案正确写法规范
此文致力于一次性解决大家关于雅思听力答案写法的困惑,大小写,日期,缩写,这里给大家重生一遍。进入考场后要牢记这些规范,避免不必要的错误。话不多说,内容自取:
雅思答案日期的写法
日月的写法
13th MAY
13th MAY
May 13th
May 13th
13 May
May 13
thirteen May
May thirteen
统一为:
May 13
13 May
May 13th
May 13th
日月年的写法
可行的有以下几种:
25 thFebruary 1975
13thJanuary, 1974 (英国)
March21st,2001(美国)
Aug.8th, 2008
02/06/2004
06/02/2004
统一为:
13 May, 1985
May 13, 1985
13th May, 1985
May 13th,1985
雅思考试听力答案写法之:常见时间写法
8:10AM
10.15 am
10.15 a.m
9.30-3.30
8.00am
8 am
统一为:
1. 数字中间统一为一个点,如10.15 am
2. 如有需要加am, pm的情况,大小写均可
3. am可以写为:a.m.或am
雅思考试听力答案写法之:大小写
按照常规区分大小写
(1)完整句句首字母需要大写。
例如:剑6 T2 S4 Q39
Sound effects were used for the first time on film in 1926.
(2)字母和数字在一起时,字母必须大写。
邮编:RA6 7BU; BH246GL
护照号:AL2880
航班号:AC937
注册会员号:UK765024EG
(3)专有名词首字母大写。
包括人名、地址、国家、语言、星球、节日、方位、书名、杂志名、电影名、职位、星期几、月份、特定的称谓等。
人名 Daniel Defoe;Professor John Smith;
地名 Chicago; Manchester;11B Lake Road; Gold Coast(黄金海岸); Tower ofLondon(伦敦塔);Greenwood Garden(绿林花园)
星期、月份 September
杂志 Fortune Magazine
不确定的情况下全部大写
不确定的情况下全部大写
不确定的情况下全部大写
雅思考试答案写法之:简称和缩写
简称
在录音中如为简称,在答案上填写简称和全称均可
录音中为ad
可写为ad或advertisement;
录音中为lab
可写为lab或laboratory;
录音中为info
可写为info或 information;
录音中为dorm
可写为dorm或dormitory
缩写
雅思官方指南中明确写出:雅思听力不考缩写,所以“自创”的或者“约定俗成”的缩写都不应作为答案填充。
(1)月份不能缩写
January 不写Jan
February 不写 Feb
March 不写Mar
April 不写 Apr
June 不写 Jun
July 不写Jul
August 不写 Aug
September 不写Sep
October 不写 Oct
November 不写 Nov
December 不写Dec
(2)星期不能缩写
Monday 不写Mon
Tuesday 不写Tue
Wednesday 不写Wed
Thursday 不写Thur
Friday 不写Fri
Saturday 不写Sat
Sunday 不写Sun
(3)时间单位不能缩写
20 minutes不能写成20m
雅思考试答案写法之:连写
连写单词
airplane 飞机
armchair 扶手椅
background 背景
baseball 垒球
bathroom 浴室
bedsit 卧室
booklet 小册子
booklist 书单
bookshop 书店
bookstore 书店
breakdowns 故障
butterfly 蝴蝶
cameraman 摄影师
centimeter 厘米
checklist 清单
childcare 儿童 照管
clockwork 发条装置
clubhouse 俱乐部
clubroom 俱乐部聚会室
coastline 海岸线
cocktail 鸡尾酒
copyright 版权
craft*en 工匠
cupboard 碗柜
darkroom 暗房
database 数据库
daylight 白天
deadline 最后期限
dishwasher 洗碗机
downhill 下坡
ecosystem 生态系统
eyesight 视力
feedback 反馈
fieldwork 野外工作
firewood 柴火
firework 烟火
flashlight 手电筒
floodwater 洪水
footbridge 行人天桥
footnote 脚注
footprint 脚印
freshwater 淡水
greenhouse 温室
handbook 手册
handout 文字材料;施舍物
hardware 计算机硬件
headphone 耳机
healthcare 医疗保健
highway 公路
homesick想家的
Homework家庭作业
keyboard键盘
landlady女房东
landmark地界标
laptop 笔记本 电脑
layout布局;设计
leaflet传单
Lifeguard 救生员
lifespan寿命
lifestyle生活方式
lighthouse 灯塔
livestock家畜
Loudspeaker扩音器
microbiology微生物学
microchip微芯片
microfilm缩微胶卷
microscope显微镜
microwave微波
midday正午
midnight午夜
minibus小型公共汽车
motorcycle 摩托车
network网络
newsletter时事通讯
newspaper报纸
northwest西北方向
notebook笔记本
online在线的
outdoor户外的
outline大纲
overdue过期的
overfill满溢
overhead在头上的
painkillers止痛药
password密码
payphone付费*
photocopy 复印件、影印本
placement布置
platform讲台
playground操场
postcard明信片
PowerPoint(专有名词考点)
railway铁路
raincoat雨衣
rainfall降雨量
rainforest雨林
restroom休息室
riverside河边
sale*an*员
sandglass沙漏
seafood海鲜
showroom 陈列室
software软件
southeast东南方向
sportswear运动装
spotlight聚光灯
stopwatch跑表
storehouse 仓库
storeroom 库房
sunlight日光
sunset日落
sunshade遮阳伞
supermarket超市
teamwork团队合作
textbook课本
thunderstorm风暴
timetable时间表
toothpaste 牙膏
underestimate 低估
undergraduate大学生
underground 地下
undersea 水下的
upland高地
upstairs楼上
videotape录像带
warehouse 仓库
waterfall 瀑布
waterproof防水材料
website 网站
wheelchair 轮椅
whiteboard白板
wildlife野生动植物
woodland森林
workbook练习薄
workforce劳动力
workload 工作量
workplace 工作场所;车间
worksheet 工作表
workshop 研讨会
分开写的单词
air conditioner 空调
alarm clock 闹钟
mass media 大众传播媒介
case study 案例研究
central heating 中央暖气系统
contact lens 隐形眼镜
notice board 布告牌
remote control 遥控
safety check 安全检查
student card 学生卡
加连字符的单词
brother-in-law 内兄/弟,姊妹的丈夫
cost-effective 划算的
detail-oriented 注重细节的
door-to-doorservice 送货上门服务
drop-offsite 下客区
drop-out 中途退学的人
fast-foodshop 快餐店
first-aidkit 急救箱
first-yearstudent 大学新生
four-coursedinner 4道菜的晚饭
full-time 专职的,全日制的
high-energysnack 高热量食品
highly-trainedstaff 高度训练的员工
large-scale 大规模的,大范围的
little-known 鲜为人知的
low-impact 低强度的
low-riskinvestment 低风险投资
middle-aged 中年的
mid-range 中点值
mid-term 期中的
non-active 不活跃的
non-fiction 纪实小说
note-taking 记笔记
part-timejob *
second-hand 二手的
self-access 可自行选用的
self-centered 自我中心的
self-defense 正当防卫
self-employed 个体经营的
self-evaluation 自我评价
self-fundedstudent 自费生
self-sufficient 自给自足的
*all-scale 小规模的
well-organized 有序的,有条理的
wheelchair-access toilet 残疾人专用厕
雅思考试听力答案写法之:数字、货币等标准替代符号
在雅思听力考试中会经常把数字、货币作为考点。
在写这一类答案的时候,既可以写成 英语单词 也可以写成*数字或者是金钱符号。
比如:
twenty=20;
ten percent=10%;
15 dollars=$15;
120 pounds=£120。
注意:关于金钱的单词要写在数字的后面,而符号要写在数字的前面。
建议大家最好使用*数字和金钱符号,这样既节省时间又可以节约空间。因为10%只算一个数字,而tenpercent则算两个单词。另外,使用这些符号也不容易犯错误。
雅思考试听力答案写法之:有发音符号的单词
有发音符号的单词,发音符号是否必须写?
如café字母e上的一撇,“café”写成“caf锓cafe”都得分。
不写撇确定给分,为了不画蛇添足,写错这一撇的位置或方向,建议不写撇.
雅思听力答案规范之:单复数问题
剑桥真题答案中,有很多单复数放在括号里。
听出单复数是最精确的拿分方案。
建议:所听即所得 上下文判断
雅思听力答案规范之:冠词
冠词a, an, the的问题:
剑桥雅思真题的答案,有些冠词是放在括号里的。
那些真题答案中放在括号里的单词:加不加都给分。
所以不写冠词即使不完全符合语法,是给分的。
而冠词又很容易听错,例如把a写成the,反而不给分。
建议:无论是否完全符合语法,在不确定的情况下,不如不写冠词。
雅思听力词汇的大小写区分
很多学生也会问到这样的问题,一个是您要明白,只要是专有名词就一定要把首字母答谢,另一个是一个专有名词,字母全部大写了也不扣分,所以其实重点就是首字母的问题,如果首字母不大写是一定要扣分的。
不知道是否说清楚了,呵呵~~简而言之,就是,专有名词首字母一定要大写,其他字母可大写可小写;如果专有名词首字母小写了,就一定扣分。
确定用大写的情况:
1)学科名,建筑名,场所名称,书名,机构名,人名,等
其中提问的标志是: what is the title/name of....., known as/called
2) 句子 第一个单词首字母
其它 情况是否用大写不是扣分点
单词一般没有明确说明是“two words”的时候,连起来写没问题。如果实在不能确定,用一下连字符。如:check-list.
剑桥雅思听力题型 总结
1、Filling out the table
You are asked to finish a chart or a table by filling the missing information.
这类题型是每次必考的,而且通常一次考试会出现多次,在4个Section中,都可能出现。
按照表格的形式,大致可分成3个类型:i. List型 ii. Table型 iii. Personal information型
2、Maps
按照地图描述的内容,大致可分为三型:
i. 街道型
一般是一个或几个街区的简易地图,已标出一些标志性建筑,需要考生根据录音内容,填上其他一些标志性建筑的名字。如,Smith Museum,Stern Park
ii. 区域型
与街道型相比,范围缩小到某一个区域,如,某一个楼面上的一些房间的方位,学校体育场地的分布等等。这一类型的地图需要考生根据录音内容,填上房间的名称或是场地的名称
iii. 摆设型
与前两个类型相比,这一类型的范围就缩小到一个较大房间的摆设了,如,办公楼大厅的摆设,图书馆中的某一个房间的内部布置等等。
按照出题的形式,可分为填空和选项两种。
3、Checking
题型介绍:
这类题型并不多见。但也是让考生比较头痛的一类题型。
按照题目的形式,可分为两种类型:
i. With headings
在一条或是几条需要判断的陈述之前,有一个标题,如,Time, Place,这一类型的出现形式和Filling out the table (General)中的List型很相似
ii. Without headings
直接是一条条的陈述,这一类型相对更常出现,难度也较有标题的要大
4、Answering the Question
题型介绍:比较常规的题型。只是要注意题设要求的回答字数的限定
5、Multiple Choice
题型介绍:
这一题型对中国考生来说应该是非常熟悉的,从小考到大,都是选择题,那么它的难度就在于录音的难度上,这类题型,一般出现在Section 3,4中。
按照出题的形式,可把这一题型,分成两类:
i. 多选一,这应该很熟悉
ii. 多选多,很多考生觉得多选多看似很难,其实多选多的考点都是一些容易听到的例子或是细节,而且题目会告诉考生要选几个,如Which three ……,考生只要当心不要遗漏就可以了
有时,选择题不是以问题加选项这种常规的方式出现,而是以图表,或是表格的形式出现,不管怎么变形,只要我们找出问题和选项,都可以还原到最常规的形式
6、Gap Filling
题型介绍:
这也就是填空题,填空题也是常考的一类题型。
7、Picture
题型介绍:
对于习惯文字题的中国考生来说,这一题型无疑是比较难的一类。
图片题涉及的范围很广,可以是食品,相貌,地点,时间,甚至是动作等等。
8、Matching
题型介绍:
配对 题在考试中,常出现在Section3、4。由于对题型的不熟悉,而且给出的配对项常常多于需要配对的问题,甚至有时选项还可以复用,问题也可以多选,一旦有听不懂的时候非常容易心虚。
9、Illustration
题型介绍:
这一题型可以说是所有题型中最难的,通常在Section 3、4中出现,但是由于题型实在太难,所以在考试中出现的频率不高。
2020雅思考试听力答案正确写法规范相关 文章 :
★ 2020年雅思听力打分标准
★ 【高分技能必备】详解雅思听力拼写及常用缩写规范
★ 2020年最新的雅思英语听力中的核心考词汇总
★ 雅思听力日期怎么书写正确
★ 雅思听力时间写法格式有哪些
★ 雅思听力考试流程和答题的注意事项,你都知道了吗?
★ 雅思听力答题卡到底该大写还是小写
★ 雅思听力审题中的常见错误,看完不丢冤枉分
★ 雅思听力考试中要注意11个基本原则
★ 雅思听力流程及注意事项介绍
托福TPO作为大家托福备考的模考工具,它的题目对我们有很大的参考价值,为了帮助大家备考,下面我给大家带来托福TPO2Part2阅读原文及参考答案,望喜欢。
托福TPO2Part2阅读原文
The Origins Of Cetaceans
It should be obvious that cetaceans-whales, porpoises, and dolphins-are mammals. They breathe through lungs, not through gills, and give birth to live young. Their streamlined bodies, the absence of hind legs, and the presence of a fluke1 and blowhole2 cannot disguise their affinities with land dwelling mammals. However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like. Extinct but already fully marine cetaceans are known from the fossil record. How was the gap between a walking mammal and a swimming whale bridged? Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans.
Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans. In 1979, a team looking for fossils in northern Pakistan found what proved to be the oldest fossil whale. The fossil was officially named Pakicetus in honor of the country where the discovery was made. Pakicetus was found embedded in rocks formed from river deposits that were 52 million years old. The river that formed these deposits was actually not far from an ancient ocean known as the Tethys Sea.
The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans. Although limited to a skull, the Pakicetus fossil provides precious details on the origins of cetaceans. The skull is cetacean-like but its jawbones lack the enlarged space that is filled with fat or oil and used for receiving underwater sound in modern whales. Pakicetus probably detected sound through the ear opening as in land mammals. The skull also lacks a blowhole, another cetacean adaptation for diving. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh-eating mammals, the mesonychids, and cetaceans. It has been suggested that Pakicetus fed on fish in shallow water and was not yet adapted for life in the open ocean. It probably bred and gave birth on land.
Another major discovery was made in Egypt in 1989. Several skeletons of another early whale, Basilosaurus, were found in sediments left by the Tethys Sea and now exposed in the Sahara desert. This whale lived around 40 million years ago, 12 million years after Pakicetus. Many incomplete skeletons were found but they included, for the first time in an archaeocyte, a complete hind leg that features a foot with three tiny toes. Such legs would have been far too *all to have supported the 50-foot-long Basilosaurus on land. Basilosaurus was undoubtedly a fully marine whale with possibly nonfunctional, or vestigial, hind legs.
An even more exciting find was reported in 1994, also from Pakistan. The now extinct whale Ambulocetus natans ("the walking whale that swam") lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetus but 9 million before Basilosaurus. The fossil luckily includes a good portion of the hind legs. The legs were strong and ended in long feet very much like those of a modern pinniped. The legs were certainly functional both on land and at sea. The whale retained a tail and lacked a fluke, the major means of locomotion in modern cetaceans. The structure of the backbone shows, however, that Ambulocetus swam like modern whales by moving the rear portion of its body up and down, even though a fluke was missing. The large hind legs were used for propulsion in water. On land, where it probably bred and gave birth, Ambulocetus may have moved around very much like a modern sea lion. It was undoubtedly a whale that linked life on land with life at sea
Fluke: the two parts that constitute the large triangular tail of a whale
1. "Blowhole: a hole in the top of the head used for breathing
Paragraph 1: It should be obvious that cetaceans-whales, porpoises, and dolphins-are mammals. They breathe through lungs, not through gills, and give birth to live young. Their streamlined bodies, the absence of hind legs, and the presence of a fluke3 and blowhole4 cannot disguise their affinities with land-dwelling mammals. However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like. Extinct but, already fully marine cetaceans are known from the fossil record. How was the gap between a walking mammal and a swimming whale bridged? Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans.
托福TPO2Part2阅读题目
Directions: Mark your answer by filling in the oval next to your choice.
1. In paragraph 1, what does the author say about the presence of a blowhole in cetaceans?
It clearly indicates that cetaceans are mammals.
It cannot conceal the fact that cetaceans are mammals.
It is the main difference between cetaceans and land-dwelling mammals.
It cannot yield clues about the origins of cetaceans.
2. Which of the following can be inferred from paragraph 1 about early sea otters?
It is not difficult to imagine what they looked like
There were great numbers of them.
They lived in the sea only.
They did not leave many fossil remains.
Paragraph 3: The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans. Although limited to a skull, the Pakicetus fossil provides precious details on the origins of cetaceans. The skull is cetacean-like but its jawbones lack the enlarged space that is filled with fat or oil and used for receiving underwater sound in modern whales. Pakicetus probably detected sound through the ear opening as in land mammals. The skull also lacks a blowhole, another cetacean adaptation for diving. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh-eating mammals, the mesonychids, and cetaceans. It has been suggested that Pakicetus fed on fish in shallow water and was not yet adapted for life in the open ocean. It probably bred and gave birth on land.
3. The word precious in the passage is closest in meaning to
Exact
Scarce
Valuable
Initial
4. Pakicetus and modern cetaceans have similar
Hearing structures
Adaptations for diving
Skull shapes
Breeding locations
5. The word it in the passage refers to
Pakicetus
Fish
Life
ocean
Paragraph 4: Another major discovery was made in Egypt in 1989. Several skeletons of another early whale, Basilosaurus, were found in sediments left by the Tethys Sea and now exposed in the Sahara desert. This whale lived around 40 million years ago, 12 million years after Pakicetus. Many incomplete skeletons were found but they included, for the first time in an archaeocyte, a complete hind leg that features a foot with three tiny toes. Such legs would have been far too *all to have supported the 50-foot-long Basilosaurus on land. Basilosaurus was undoubtedly a fully marine whale with possibly nonfunctional, or vestigial, hind legs.
6. The word exposed in the passage is closest in meaning to
Explained
Visible
Identified
Located
7. The hind leg of Basilosaurus was a significant find because it showed that Basilosaurus
Lived later than Ambulocetus natans
Lived at the same time as Pakicetus
Was able to swim well
Could not have walked on land
8. It can be inferred that Basilosaurus bred and gave birth in which of the following locations
On land
Both on land and at sea
In shallow water
In a marine environment
Paragraph 5: An even more exciting find was reported in 1994, also from Pakistan. The now extinct whale Ambulocetus natans ("the walking whale that swam") lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetus but 9 million before Basilosaurus. The fossil luckily includes a good portion of the hind legs. The legs were strong and ended in long feet very much like those of a modern pinniped. The legs were certainly functional both on land and at sea. The whale retained a tail and lacked a fluke, the major means of locomotion in modern cetaceans. The structure of the backbone shows, however, that Ambulocetus swam like modern whales by moving the rear portion of its body up and down, even though a fluke was missing. The large hind legs were used for propulsion in water. On land, where it probably bred and gave birth, Ambulocetus may have moved around very much like a modern sea lion. It was undoubtedly a whale that linked life on land with life at sea
9. Why does the author use the word luckily in mentioning that the Ambulocetus natans fossil included hind legs?
Fossil legs of early whales are a rare find.
The legs provided important information about the evolution of cetaceans.
The discovery allowed scientists to reconstruct a complete skeleton of the whale.
Until that time, only the front legs of early whales had been discovered.
10. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?
Incorrect choices change the meaning in important ways or leave out essential information.
Even though Ambulocetus swam by moving its body up and down, it did not have a backbone.
The backbone of Ambulocetus, which allowed it to swim, provides evidence of its missing fluke.
Although Ambulocetus had no fluke, its backbone structure shows that it swam like modern whales.
By moving the rear parts of their bodies up and down, modern whales swim in a different way from the way Ambulocetus swam.
11. The word propulsion in the passage is closest in meaning to
Staying afloat
Changing direction
Decreasing weight
Moving forward
Paragraph 1: Extinct but already fully marine cetaceans are known from the fossil record. ■How was the gap between a walking mammal and a swimming whale bridged? ■Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans.■Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans. ■In 1979, a team looking for fossils in northern Pakistan found what proved to be the oldest fossil whale.
12. Look at the four squares [■] that indicate where the following sentence can be added to the passage.
This is a question that has puzzled scientists for ages.
Where would the sentence best fit?
13-14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
This passage discusses fossils that help to explain the likely origins of cetaceans-whales, porpoises, and dolphins.
●
●
●
Answer Choices
1. Recent discoveries of fossils have helped to show the link between land mammals and cetaceans.
2. The discovery of Ambulocetus natans provided evidence for a whale that lived both on land and at sea.
3. The skeleton of Basilosaurus was found in what had been the Tethys Sea, an area rich in fossil evidence.
4. Pakicetus is the oldest fossil whale yet to be found.
5. Fossils thought to be transitional forms between walking mammals and swimming whales were found.
6. Ambulocetus' hind legs were used for propulsion in the water
托福TPO2Part2 阅读答案
参考答案:
1、2
2、1
3、3
4、3
5、1
6、2
7、4
8、4
9、2
10. 3
11. 4
12. 2
13-14. 1 2 5
托福TPO2Part2阅读原文翻译
沙漠已经占据了地球表面积约四分之一,而且最近几十年正以惊人的速度扩张。沙漠化是指类似沙漠的环境漫延到原本并非沙漠的区域。据估计,地球表面另外四分之一的地方正面临沙漠化威胁。
沙漠化主要通过以下过程实现:首先自然植被不断减少,随后风力和 雨水 加速了土壤的腐蚀。有的时候松散的土壤全部被风刮走,留下石质化的表层; 其它 情况下细小的沙粒可能会被吹走,而正常沙粒大小的砂子不断堆积,从而形成移动的沙丘或者沙脊。
即便是在保留了土壤表层的区域,植被减少也已成为土壤大量吸取地下水的能力下降的典型因素。雨水对松散土壤的冲击会把细小的粘土颗粒冲到土壤空隙中,封闭了土壤并降低土地表层水的渗透率。地表对水的吸收急剧减少,大量水资源流失,因此土壤的腐蚀率也随即增加。地表吸收水分的能力进一步弱化使得土壤越发干燥,导致植被的进一步流失,于是便形成了土壤沙漠化的恶性循环。
在一些地方,沙漠面积的扩大很大程度上归因于干燥的气候条件。在过去的几千年里,不断增加的温室效应使得一些地方干旱问题愈发严重。倘若空气污染带来的温室效应继续恶化,沙漠化进程会在未来数十年内加速实现。
然而,可以肯定的是,大部分地区沙漠化主要都是由于人类活动造成,而非自然条件导致。沙漠边缘的半干旱土地所处的生态平衡环境非常脆弱,环境压力持续增加,而这些半干旱区域适应环境压力的能力极其有限。人口数量的增加使得人们不断向土地施压,依其提供食物和燃料。在湿润的季节里,土地兴许能够应付这些压力。但是在干旱的季节里,在沙漠周边的土地上,存在着这样一个十分普遍的现象:人类对土地施加的压力远远超过了土地自身减压的能力,因此最终形成了沙漠。
导致沙漠化的主要因素有四个:过度 种植 ,过度放牧,过分砍伐,过度灌溉。由于人口密度增加,人们对粮食作物的种植已经扩展到日益干燥的区域进行。这些区域很有可能经常会发生干旱,所以农作物种植失败是很正常的事情。大多数农作物的种植需要事先移除天然植被,而农作物欠收后又会留下大面积荒地,非常容易被风力和雨水侵蚀。
在半干旱地区,草坪是主要的天然植被,家畜 饲养 是当地的一项主要经济活动。在一个地区过量饲养家畜会导致植被覆盖面积减少,土地被大量践踏和碾碎。通常,随之而来的就是土地硬化和加速侵蚀。
在很多国家木材是用来做饭和加热的最主要燃料。人口增加带来的压力促使人们大量砍伐木材,导致许多城市和乡村周围大面积树木和灌木减少。同时人们大量使用烘干的动物排泄物作为替代燃料同样对土壤不利,因为这些珍贵的土壤成分调节剂和植物营养资源将不会再回归至土壤当中。
造成土地沙漠化的最后一个主要人为因素在于人类过度灌溉导致土壤的盐碱化。灌溉多余的水渗透到地下水位。假如没有排水系统的存在,那么地下水位上升,把溶解的盐分带到土壤表面。水分蒸发后,盐分留在了表面,形成白色的地壳层,这一地壳层阻止了空气和水接触地底下的土壤。
沙漠化问题异常严重,这是因为有佷广阔的地区和数量庞大的人群都受到了沙漠化的影响,而且要想逆转沙漠化的进程甚至减缓沙漠化的速度都面临着巨大的困难。一旦土壤被侵蚀,需要再经过几百到上千年的时间才会产生新的土壤。那些大量土壤仍保存完好的地方,亟需一个严谨而有力的保护政策和植被覆盖计划来保护现有土地。
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