Up to one fifth of the Amazon rainforest is emitting more CO2 than it absorbs, new research suggests.
最新研究表明，多达五分之一的亚马孙雨林排放的二氧化碳比吸收的还要多。
Results from a decade-long study of greenhouse gases over the Amazon basin appear to show around 20% of the total area has become a net source of carbon dioxide in the atmosphere.
对亚马孙流域温室气体的一项长达十年的研究结果显示，该流域中大约有20%的地区已成为大气中二氧化碳的净来源地。
One of the main causes is deforestation.
造成这一现象的主要原因之一是森林砍伐。
While trees are growing they absorb carbon dioxide from the atmosphere; dead trees release it again.
树木生长时，会从大气中吸收二氧化碳，死亡的树木会再次释放二氧化碳。
Millions of trees have been lost to logging and fires in recent years.
近年来，数百万棵树木被砍伐或被火灾烧毁。
The results of the study, which have not yet been published, have implications for the effort to combat climate change.
这项尚未发表的研究结果对应对气候变化的努力具有启示意义。
They suggest that the Amazon rainforest - a vital carbon store, or "sink", that slows the pace of global warming - may be turning into a carbon source faster than previously thought.
研究认为，作为至关重要的碳储存地（或称“碳汇”），亚马孙雨林减缓了全球变暖的步伐，而它转变为碳排放源的速度可能比之前预想的要快。
Every two weeks for the past 10 years, a team of scientists led by Prof Luciana Gatti, a researcher at Brazil's National Institute for Space Research (INPE), has been measuring greenhouse gases by flying aircraft fitted with sensors over different parts of the Amazon basin.
过去10年里，每隔两周，由巴西国家空间研究所研究员卢西亚纳·加蒂教授领导的一个科学家团队，就会在亚马孙流域的不同区域，通过安装传感器的飞行器来测量温室气体。
What the group found was startling: while most of the rainforest still retains its ability to absorb large quantities of carbon dioxide - especially in wetter years - one portion of the forest, which is especially heavily deforested, appears to have lost that capacity.
该小组的发现令人震惊：虽然大部分雨林仍然保持着吸收大量二氧化碳的能力——尤其是在更湿润的年份，但森林的一部分，尤其是大量被砍伐的森林，似乎已经失去了这种能力。
Gatti's research suggests this south-eastern part of the forest, about 20% of the total area, has become a carbon source.
加蒂的研究表明，亚马孙雨林的东南部（约占总面积的20%）已经成为一个碳源。
"Each year is worse," she told Newsnight.
“一年比一年糟糕，”加蒂告诉夜间新闻栏目。

"We observed that this area in the south-east is an important source of carbon. And it doesn't matter whether it is a wet year or a dry year. 2017-18 was a wet year, but it didn't make any difference."
“我们观察到，东南地区是二氧化碳的重要来源，而且无关年份干燥还是湿润。2017-2018年是湿润的一年，但没有什么变化。”
A forest can become a source of carbon rather than a store, or sink, when trees die and emit carbon into the atmosphere.
当树木死亡并向大气排放二氧化碳时，森林就会成为二氧化碳的来源，而不是二氧化碳的储存地或森林碳汇。
Areas of deforestation also contribute to the Amazon's inability to absorb carbon.
森林被砍伐的区域也导致了亚马孙雨林无法吸收碳。
Carlos Nobre, who co-authored Prof Gatti's study, called the observation "very worrying" because "it could be showing the beginnings of a major tipping point".
加蒂教授研究报告的合著者卡洛斯·诺布雷称，这一观察结果“非常令人担忧”，因为“它可能显示出一个重大转折点的开端”。
He believes the new findings suggest that in the next 30 years, more than half of the Amazon could transform from rainforest into savanna.
诺布雷认为，新的发现表明，在未来30年内，超过一半的亚马孙雨林可能会从热带雨林变成热带草原。
For decades, scientists have warned of an "Amazon tipping-point": the point at which the forest loses its ability to renew itself and begins to emit more carbon than it absorbs.
几十年来，科学家们一直对“亚马孙临界点”发出警告。在这个临界点上，森林将失去自我更新的能力，释放的二氧化碳比吸收更多。
"[The Amazon] used to be, in the 1980s and 90s, a very strong carbon sink, perhaps extracting two billion tonnes of carbon dioxide a year from the atmosphere," says Prof Nobre, who is also a researcher at the University of Sao Paulo's Institute for Advanced Studies and Brazil's leading expert on the Amazon.
“亚马孙雨林在上世纪八九十年代是一个非常强大的碳汇，大概每年能从大气中吸收二十亿吨的二氧化碳，”诺布雷教授说，他是圣保罗大学高级研究所的研究员，也是巴西亚马孙雨林研究领域领先的专家。
"Today, that strength is reduced perhaps to 1-1.2bn tonnes of carbon dioxide a year."
“如今，这一吸收能力可能已降至每年10至12亿吨二氧化碳。”
Opinions on when this tipping point could occur differs among scientists.
关于这个临界点何时会出现，科学家们的看法各不相同。
"Some people think that it won't be until three-degrees warming - so towards the end of the century, whereas other people think that we could get [it with] deforestation up above 20% or so and that might happen in the next decade or two. So it's really, really uncertain," explained Simon Lewis, professor of global change science at UCL.
伦敦大学学院全球变化科学教授西蒙·路易斯解释道：“有些人认为，到本世纪末气温上升3摄氏度才会出现临界点。而另一些人则认为，如果森林砍伐率上升大约20%就会达到临界点，这种情况可能会在未来10年或20年内出现。所以是非常不确定的。”