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　　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.
如果人类对目前加速中的气候变迁有责任的话，其实可能并非第一次。科学家说，很久以前在非洲中部，早期农夫可能造成雨林的消失。新一期《科学》期刊提出了这个问题。
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.
科学家说，大约3千年前，一部分的雨林被大草原“突然取代”，形成了点缀着灌木和树的广阔草地。原来的研究认为气候变迁是原因。但现在的研究显示，光是气候变迁可能无法造成这么突然的改变，人类也许也是原因之一。
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.
拜杨博士为一家法国研究机构作研究。他说，非洲的农业史跟欧洲或亚洲的农业史相比之下鲜少人知。
“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.
拜杨说：“农业才刚开始就对环境造成了冲击。在非洲，我猜因为相关研究少很多，所以它们之间的关系没有很清楚。”
Telltale mud
Bayon and his colleagues have been studying sediment⁶ at the mouth of the Congo River.
拜杨和他的同事一直在刚果河口研究该地的沉积现象。
“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.
拜杨说：“基本上，我们分析在刚果河取得的沉积物。沉积物在这个地点不断累积，这让我们有了微粒的完整记录，这些微粒是从刚果河长期以来流出的。”
The sediment tells the story of the Congo Basin climate.
沉积物解释了刚果盆地的气候。
“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.
拜杨说：“中非的气候在1万年前到5千年前潮湿许多。之后气候就开始恶化。但气候在4千年前之后才开始变得比较干燥，当然植物对这个气候变迁也作出了反应。”
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.
这就是大草原开始出现之时。但拜杨说，可能还有其他重要的因素，例如侵蚀和土壤的化学风化。
“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.
拜杨说：“所以基本上，非洲下越多雨，土壤就被侵蚀地越多。我们的研究显示，从3千年前之后，侵蚀风化作用就变得完全不显著。所以我们想，这并不只是气候改变引发的，我们必须将其他事情一并考量进来。”
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.
班图人进入了现在的尼日利亚和喀麦隆的边界地区。拜杨说，他们将农业和炼铁带到了刚果盆地。证据显示，他们的主要作物之一是珍珠粟。而这在很多方面说明了当时的气候状况。
“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.
拜杨说：“湿热的气候不适合珍珠粟的耕种。它必须有乾季和雨季交替。这显示了将农业引进雨林的关键原因是要建立这种更为明确的季节习性。”
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.
为了生产珍珠粟，班图人需要开阔的田地。这代表要清除大片雨林，这使得土地暴露于侵蚀，进一步导致了刚果河口为我们揭秘的沉积现象。所以拜杨说，可能是农夫加上气候变迁造成了雨林消失。
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?
他说，这个情况存在1千年前到1千5百年前这个时期。之后又开始发生改变。雨林开始变多。就在这个时候，班图人前往非洲其他地方。问题在于，班图人离开是因为雨林重新生长，还是雨林重新生长是因为班图人将农业带走？
“This, I must admit,” said Bayon, “is something which is a bit puzzling and which is not well known at present, I think.”
拜杨说：“我必须承认，这有点令人费解，我想现在无法得知。”
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.
他说，无论如何，证据显示就算在3千年前人类已经对环境有重大影响。目前已知，农业会增加碳排放，树木会吸收碳以阻止碳排入大气层。在班图人留在中非的那段时期，农业变多、树变少。