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.
研究人员上周撰文称，亚马孙森林吸收二氧化碳的能力正在逐渐削弱。这一研究结果显示，遏制气候变化可能比预期的更加困难。
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.
几十年来，人类排放到大气中的二氧化碳污染，有将近一半都会被森林和海洋吸收。这抑制了地球因为那些排放而变暖的程度。

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.
尽管二氧化碳排放急剧提高，但是森林和海洋的吸收能力基本上跟上了增长的步伐。这让许多科学家感到意外，不过也令一些人发出了警告：不能指望这样一个强劲的碳吸收源永远运转下去。
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.
由英国利兹大学(University of Leeds)一个研究小组引领的研究人员，持续30年对亚马孙盆地321块林地中的18.9万棵树进行了研究。他们发现，亚马孙森林吸收二氧化碳的总量在20世纪90年代达到峰值，每年约20亿吨，自那时以来已经下降了一半。
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.
研究人员最初推断，面对二氧化碳水平的提升，亚马孙森林可能应对良好，二氧化碳可以促进植物生长。但是亚马孙森林的应对能力似乎正在减弱。干旱和其他问题似乎也起到了一定影响，不过主要的因素似乎是最初生长速度的加快，加速了树木的新陈代谢。
“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.
“随着时间的推移，刺激生长的效应传到整个系统，导致树木长得更快，所以也死得更早，”利兹大学热带生态学家奥利弗·L·菲利普斯(Oliver L. Phillips)和另一位在研究中牵头的人物在一份声明中说道。
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.
虽然还需要进一步开展研究，但科学家表示，假定亚马孙森林会持续吸收大量二氧化碳的气候预测模型，可能过于乐观了。
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，研究显示森林吸收的碳仍然远远超出它们向大气中释放的碳，尽管由气候变化造成的火灾、虫害等消极事件有所增加。简而言之，在全世界的森林中，树木生长的趋势远远超出了树木死亡的趋势。
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?
现在最大的问题或许是，这种局面会不会发生逆转。亚马孙之外的森林，如环绕北半球的针叶林带，是不是最终也会像亚马孙森林一样，减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.
那实际上意味着，人类文明能从树木那里得到的帮助就会减少，削减二氧化碳排放的力度，需要超出过去预想的力度，以将全球变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.”
“森林给我们帮了大忙，但是我们不能靠它们来解决碳排放的问题，”菲利普斯说。“要想稳定我们的环境，还是需要更有力地削减排放。”