研究：1/5亞馬孫雨林排碳多於吸碳
亞馬孫雨林產生的氧氣佔全球氧氣總量的1/10，因此被稱爲“地球之肺”。而最新的一項研究表明，“地球之肺”如今可能要保不住了。亞馬孫雨林中大約20%的流域排出的二氧化碳已經多於吸收量。
Up to one fifth of the Amazon rainforest is emitting more CO2 than it absorbs, new research suggests.
最新研究表明，多達五分之一的亞馬孫雨林排放的二氧化碳比吸收的還要多。
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.
對亞馬孫流域溫室氣體的一項長達十年的研究結果顯示，該流域中大約有20%的地區已成爲大氣中二氧化碳的淨來源地。
One of the main causes is deforestation.
造成這一現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.
樹木生長時，會從大氣中吸收二氧化碳，死亡的樹木會再次釋放二氧化碳。
Millions of trees have been lost to logging and fires in recent years.
近年來，數百萬棵樹木被砍伐或被火災燒燬。
The results of the study, which have not yet been published, have implications for the effort to combat climate change.
這項尚未發表的研究結果對應對氣候變化的努力具有啓示意義。
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.
研究認爲，作爲至關重要的碳儲存地（或稱“碳匯”），亞馬孫雨林減緩了全球變暖的步伐，而它轉變爲碳排放源的速度可能比之前預想的要快。
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.
過去10年裏，每隔兩週，由巴西國家空間研究所研究員盧西亞納•加蒂教授領導的一個科學家團隊，就會在亞馬孫流域的不同區域，通過安裝傳感器的飛行器來測量溫室氣體。
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.
該小組的發現令人震驚：雖然大部分雨林仍然保持着吸收大量二氧化碳的能力——尤其是在更溼潤的年份，但森林的一部分，尤其是大量被砍伐的森林，似乎已經失去了這種能力。
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，亞馬孫雨林的東南部（約佔總面積的20%）已經成爲一個碳源。
"Each year is worse," she told Newsnight.
“一年比一年糟糕，” 加蒂告訴夜間新聞欄目。
"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."
“我們觀察到，東南地區是二氧化碳的重要來源，而且無關年份乾燥還是溼潤。2017-2018年是溼潤的一年，但沒有什麼變化。”
A forest can become a source of carbon rather than a store, or sink, when trees die and emit carbon into the atmosphere.
當樹木死亡並向大氣排放二氧化碳時，森林就會成爲二氧化碳的來源，而不是二氧化碳的儲存地或森林碳匯。
Areas of deforestation also contribute to the Amazon's inability to absorb carbon.
森林被砍伐的區域也導致了亞馬孫雨林無法吸收碳。
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".
加蒂教授研究報告的合著者卡洛斯•諾佈雷稱，這一觀察結果“非常令人擔憂”，因爲“它可能顯示出一個重大轉折點的開端”。
tipping point：n.臨界點；引爆點
He believes the new findings suggest that in the next 30 years, more than half of the Amazon could transform from rainforest into savanna.
諾佈雷認爲，新的發現表明，在未來30年內，超過一半的亞馬孫雨林可能會從熱帶雨林變成熱帶草原。
savanna[sə'vænə]：n.熱帶草原
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.
幾十年來，科學家們一直對“亞馬孫臨界點”發出警告。在這個臨界點上，森林將失去自我更新的能力，釋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.
“亞馬孫雨林在上世紀八九十年代是一個非常強大的碳匯，大概每年能從大氣中吸收二十億噸的二氧化碳，”諾佈雷教授說，他是聖保羅大學高級研究所的研究員，也是巴西亞馬孫雨林研究領域領先的專家。
"Today, that strength is reduced perhaps to 1-1.2bn tonnes of carbon dioxide a year."
“如今，這一吸收能力可能已降至每年10至12億噸二氧化碳。”
Opinions on when this tipping point could occur differs among scientists.
關於這個臨界點何時會出現，科學家們的看法各不相同。
"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.
倫敦大學學院全球變化科學教授西蒙·路易斯解釋道：“有些人認爲，到本世紀末氣溫上升3攝氏度纔會出現臨界點。而另一些人則認爲，如果森林砍伐率上升大約20%就會達到臨界點，這種情況可能會在未來10年或20年內出現。所以是非常不確定的。”
