研究顯示亞馬孫森林吸收二氧化碳能力減弱

The ability of the Amazon forest to soak up excess carbon dioxide is weakening over time, researchers reported last week. That finding suggests that limiting climate change could be more difficult than expected.

研究人員上週撰文稱，亞馬孫森林吸收二氧化碳的能力正在逐漸削弱。這一研究結果顯示，遏制氣候變化可能比預期的更加困難。

For decades, Earth’s forests and seas have been soaking up roughly half of the carbon pollution that people are pumping into the atmosphere. That has limited the planetary warming that would otherwise result from those emissions.

幾十年來，人類排放到大氣中的二氧化碳污染，有將近一半都會被森林和海洋吸收。這抑制了地球因爲那些排放而變暖的程度。

The forests and oceans have largely kept up even as emissions have skyrocketed. That surprised many scientists, but also prompted warnings that such a robust “carbon sink” could not be counted on to last forever.

儘管二氧化碳排放急劇提高，但是森林和海洋的吸收能力基本上跟上了增長的步伐。這讓許多科學家感到意外，不過也令一些人發出了警告：不能指望這樣一個強勁的碳吸收源永遠運轉下去。

In a vast study spanning 30 years and covering 189,000 trees distributed across 321 plots in the Amazon basin, researchers led by a group at the University of Leeds, in Britain, reported that the uptake of carbon dioxide in the Amazon peaked in the 1990s, at about 2 billion tons a year, and has since fallen by half.

由英國利茲大學(University of Leeds)一個研究小組引領的研究人員，持續30年對亞馬孫盆地321塊林地中的18.9萬棵樹進行了研究。他們發現，亞馬孫森林吸收二氧化碳的總量在20世紀90年代達到峯值，每年約20億噸，自那時以來已經下降了一半。

Initially, the researchers postulated, the Amazon may have responded well to rising carbon dioxide levels, which are known to increase plant growth, but that response appears to be tapering off. Drought and other stresses could be playing a role, but the main factor seems to be that the initial acceleration of growth sped up the metabolism of the trees.

研究人員最初推斷，面對二氧化碳水平的提升，亞馬孫森林可能應對良好，二氧化碳可以促進植物生長。但是亞馬孫森林的應對能力似乎正在減弱。乾旱和其他問題似乎也起到了一定影響，不過主要的因素似乎是最初生長速度的加快，加速了樹木的新陳代謝。

“With time, the growth stimulation feeds through the system, causing trees to live faster, and so die younger,” Oliver L. Phillips, a tropical ecologist at the University of Leeds and one of the leaders of the research, said in a statement.

“隨着時間的推移，刺激生長的效應傳到整個系統，導致樹木長得更快，所以也死得更早，”利茲大學熱帶生態學家奧利弗·L·菲利普斯(Oliver L. Phillips)和另一位在研究中牽頭的人物在一份聲明中說道。

Further research is needed, but the scientists say that climate forecasting models that assume a continuing, robust carbon sink in the Amazon could be overly optimistic.

雖然還需要進一步開展研究，但科學家表示，假定亞馬孫森林會持續吸收大量二氧化碳的氣候預測模型，可能過於樂觀了。

At a global scale, studies suggest that forests are still absorbing far more carbon than they release into the atmosphere, even as stresses like fires and beetle attacks increase because of climate change. In essence, rising forces of growth have been outracing rising forces of death in the world’s forests.

在全球尺度上，研究顯示森林吸收的碳仍然遠遠超出它們向大氣中釋放的碳，儘管由氣候變化造成的火災、蟲害等消極事件有所增加。簡而言之，在全世界的森林中，樹木生長的趨勢遠遠超出了樹木死亡的趨勢。

Perhaps the big question now is whether that will flip. Will forests beyond the Amazon, such as the boreal forest that encircles the Northern Hemisphere, eventually follow the Amazon and weaken as carbon sinks?

現在最大的問題或許是，這種局面會不會發生逆轉。亞馬孫之外的森林，如環繞北半球的針葉林帶，是不是最終也會像亞馬孫森林一樣，減弱吸收二氧化碳的能力？

That would mean, in effect, that human civilization would have less help from trees, and cuts in carbon emissions would need to be sharper than previously thought to limit global warming to tolerable levels.

那實際上意味着，人類文明能從樹木那裏得到的幫助就會減少，削減二氧化碳排放的力度，需要超出過去預想的力度，以將全球變暖控制在可接受的水平。

“Forests are doing us a huge favor, but we can’t rely on them to solve the carbon problem,” Dr. Phillips said. “Instead, deeper cuts in emissions will be required to stabilize our climate.”

“森林給我們幫了大忙，但是我們不能靠它們來解決碳排放的問題，”菲利普斯說。“要想穩定我們的環境，還是需要更有力地削減排放。”