VOA标准英语2012--Did Early Man Contribute to Central Africa Climate Change?

Did Early Man Contribute to Central Africa Climate Change?

If humans are responsible for speeding the climate change currently underway, it may not be the first time. Scientists say a long time ago in Central Africa, early farmers may have contributed to the disappearance¹ of rainforests. The question is being raised in the journal Science.
Scientists say about 3,000 years ago some of the rainforests were “abruptly replaced” by savannas² – broad grasslands³ dotted with shrubs⁴ and trees. It was thought that climate change was the reason. But now research suggests that climate change alone could not be responsible for the sudden shift -- that perhaps people played a part.
Dr. Germain Bayon, who works for a French research institute, said much less is known about the agricultural history of Africa than either Europe or Asia.
“The onset⁵ of agriculture had already an impact on the environment, whereas in Africa, I guess because there have been (a lot fewer ) studies done, the link was not very clear,” he said.
Telltale mud
Bayon and his colleagues have been studying sediment⁶ at the mouth of the Congo River.
“Basically, we analyzed⁷ the sediment core, which was recovered off the Congo River. Sediments⁸ have been accumulating at this site… which provide an integrated record of the particles, which have been discharged by the Congo River through time,” he said.
The sediment tells the story of the Congo Basin climate.
“The climate in Central Africa was much more humid between about 10,000 years ago and 5,000 years ago. And then the climate started to deteriorate⁹. So, it’s only after about 4,000 years ago that the climate started to become dryer¹⁰ and of course the vegetation responded to this climate change,” said Bayon.
That’s when the savannahs started to appear. But Bayon said there may be other major contributing factors, such as erosion and the chemical weathering of soil.
“So, basically, the more it rains in Africa, the more the soils were being eroded¹¹. And what we showed is that from 3,000 years ago the weathering erosion signal became completely decoupled from the climatic signal. And this we think is a sign that this event was not only triggered by a change in the climate. And we need to take something else into account,” he said.
Migration¹² of the Bantu
Enter the Bantu people from what is now the border area between Nigeria and Cameroon. Bayon said they brought farming and iron smelting¹³ to the Congo Basin. Evidence shows one of the main crops was pearl millet¹⁴. And that in itself says a lot about the climate.
“Pearl millet to be cultivated actually doesn’t like the warm climate, humid climate. It requires alternating between a dry season and a wet season. It shows that the key factor for introducing agriculture into the rainforest was the establishment of this more pronounced seasonality¹⁵. This alternates between wet and dry seasons,” he said.
To grow pearl millet and other crops, the Bantu needed open fields. That meant clearing large areas of rainforest. That in turn exposed the land to erosion and resulted in the telltale sediment at the mouth of the Congo River. So, it’s possible, said Bayon, the farmers along with climate change helped the rainforests to disappear.
The period lasted between 1,000 and 1500 years. Then things started to change again. The rainforests began to return. About the same time, the Bantu left for other parts of Africa. The question is: did the Bantu leave because the rainforests started to regrow or did the rainforests regrow because the Bantu left and took their farming with them?
“This, I must admit,” said Bayon, “is something which is a bit puzzling and which is not well known at present, I think.”
Bayon said, however, what the evidence does show is that even 3,000 years ago humans could have a major impact on the environment. It’s now known that agriculture contributes to carbon emissions¹⁶ and that trees help trap that carbon and keep it from the atmosphere. During the Bantu’s stay in Central Africa, there was more agriculture and fewer trees.

1 disappearance   

n.消失，消散，失踪

参考例句：

• He was hard put to it to explain her disappearance.他难以说明她为什么不见了。
• Her disappearance gave rise to the wildest rumours.她失踪一事引起了各种流言蜚语。

2 savannas   

n.（美国东南部的）无树平原( savanna的名词复数 )；（亚）热带的稀树大草原

参考例句：

• Therefore the jungles and the savannas know of no juvenile delinquency! 因此，丛林和荒原里没有“少年犯罪。” 来自辞典例句
• My soul flits away into the virgin forests and to the savannas. 我的灵魂飞向森林中的处女地和广漠的平原。 来自互联网

3 grasslands   

n.草原，牧场( grassland的名词复数 )

参考例句：

• Songs were heard ringing loud and clear over the grasslands. 草原上扬起清亮激越的歌声。 来自《现代汉英综合大词典》
• Grasslands have been broken and planted to wheat. 草原已经开垦出来，种上了小麦。 来自《简明英汉词典》

4 shrubs   

灌木( shrub的名词复数 )

参考例句：

• The gardener spent a complete morning in trimming those two shrubs. 园丁花了整个上午的时间修剪那两处灌木林。
• These shrubs will need more light to produce flowering shoots. 这些灌木需要更多的光照才能抽出开花的新枝。

5 onset   

n.进攻，袭击，开始，突然开始

参考例句：

• The drug must be taken from the onset of the infection.这种药必须在感染的最初期就开始服用。
• Our troops withstood the onset of the enemy.我们的部队抵挡住了敌人的进攻。

6 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

7 analyzed   

v.分析( analyze的过去式和过去分词 )；分解；解释；对…进行心理分析

参考例句：

• The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
• The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程，因为对他来说，爱是个不可分析的迷。 来自《简明英汉词典》

8 sediments   

沉淀物( sediment的名词复数 )； 沉积物

参考例句：

• When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后，体积的70-80％是水。
• Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。

9 deteriorate   

v.变坏；恶化；退化

参考例句：

• Do you think relations between China and Japan will continue to deteriorate?你认为中日关系会继续恶化吗？
• He held that this would only cause the situation to deteriorate further.他认为，这只会使局势更加恶化。

10 dryer   

n.干衣机，干燥剂

参考例句：

• He bought a dryer yesterday.他昨天买了一台干燥机。
• There is a washer and a dryer in the basement.地下室里有洗衣机和烘干机。

11 eroded   

adj. 被侵蚀的，有蚀痕的 动词erode的过去式和过去分词形式

参考例句：

• The cliff face has been steadily eroded by the sea. 峭壁表面逐渐被海水侵蚀。
• The stream eroded a channel in the solid rock. 小溪在硬石中侵蚀成一条水道。

12 migration   

n.迁移，移居，（鸟类等的）迁徙

参考例句：

• Swallows begin their migration south in autumn.燕子在秋季开始向南方迁移。
• He described the vernal migration of birds in detail.他详细地描述了鸟的春季移居。

13 smelting   

n.熔炼v.熔炼，提炼（矿石）( smelt的现在分词 )

参考例句：

• a method of smelting iron 一种炼铁方法
• Fire provided a means of smelting ores. 火提供了熔炼矿石的手段。 来自辞典例句

14 millet   

n.小米，谷子

参考例句：

• Millet is cultivated in the middle or lower reaches of the Yellow River.在黄河中下游地区，人们种植谷子。
• The high quality millet flour was obtained through wet milling.采用湿磨法获得了高品质的小米粉。

15 seasonality   

季节性

参考例句：

• a high degree of climatic seasonality 明显的季节性气候变化
• Confinement. Seasonality of tourist trade, animals often 'contracted' to work. 限制，在旅游旺季时，动物们通常都得被迫“上工”。 来自互联网

16 emissions   

排放物( emission的名词复数 )； 散发物（尤指气体）

参考例句：

• Most scientists accept that climate change is linked to carbon emissions. 大多数科学家都相信气候变化与排放的含碳气体有关。
• Dangerous emissions radiate from plutonium. 危险的辐射物从钚放散出来。