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We know there's CO2 fertilization, okay?
我们知道二氧化碳施肥的存在，对吧？
Scott Denning, a climate scientist at Colorado State University, says the question is not whether carbon dioxide helps plants grow better; that can be shown in the lab with the photosynthesizing organelles in leaves called chloroplasts.
科罗拉多州立大学的气候科学家斯科特·丹宁说，问题不在于二氧化碳是否有助于植物更好地生长；这一点可以在实验室通过叶片中的光合作用细胞器叶绿体来证明。
If I take some chloroplasts, and I put them in a test tube, and I increase the concentration of dissolved CO2 in that test tube, the chloroplasts will make more sugar.
如果把一些叶绿体放入试管中，增加试管中溶解的二氧化碳的浓度，叶绿体就会产生更多的糖。
Down at the molecular scale, there's absolutely no question that CO2 increases the rates of photosynthesis.
从分子水平来看，毫无疑问，二氧化碳会增加光合作用的速率。
But do individual trees and entire forests benefit when CO2 increases the rate of photosynthesis?
但是，当二氧化碳提高光合作用的速率时，个别树木和整个森林是否会因此受益呢？
Thirty years ago researchers at Duke University conducted the first experiment to find out.
30年前，杜克大学的研究人员进行了第一次实验，试图找出答案。
They mounted pipes on rings of towers built around pine plots and blew carbon dioxide into the areas inside.
他们在松林周围建造的塔环上安装管道，并向内部区域注入二氧化碳。
After eight years these forests had stored about 30 percent more carbon than control plots.
八年后，这些森林储存的碳量比对照地块多了约30%。
There have since been several other carbon fertilization experiments in forests, but some have not demonstrated any long-term gains in carbon uptake.
自那以后，人们还在森林中进行了其他几项碳肥试验，但其中一些试验并未证明在碳吸收方面有任何长期收益。
Scott says that one reason why could be that more plant growth might not always translate into more carbon stored in wood and soil.
斯科特说，其中一个原因可能是，植物生长的更快可能并不总是能转化为将更多的碳储存在木材和土壤中。
And the more CO2 you fix into leaves, for example, then the more leaves fall off and therefore the more decomposition you get.
例如，树叶中吸收的二氧化碳越多，它就会掉得越多，于是分解出来的二氧化碳也越多。
Since nobody has run a carbon fertilization experiment in any tropical forest, the effect's possible benefits to the Amazon aren't known.
由于没有人在任何热带森林中进行过碳肥试验，所以这种效应对亚马逊地区可能产生的影响也不得而知。
If this CO2 fertilization effect really exists-and in the magnitude we theorize it exists-then the forest would basically stay there the way it is.
如果二氧化碳施肥效应真的存在--并且它的效果跟我们的理论一致--那么森林基本上会保持原状。
If it doesn't, then we would go towards something like a dieback.
如果它不存在，那我们终将走向所谓的“枯梢病”之路。
“Dieback” is a technical term for the Amazon's potential death spiral.
“枯梢病”是专业术语，指亚马逊可能出现的螺旋死亡。
The idea is that hotter, drier conditions could slow tree growth, reducing uptake of carbon, which would increase global temperatures in a vicious cycle.
这种想法是，更热、更干燥的条件可能会减缓树木的生长，进而减少碳吸收，形成恶性循环，加剧全球升温。
Certain scenarios predict that you would have a climate here-regional climate-that would not sustain a forest anymore.
某些情景预测，这种气候，地区性气候，将无法再维持雨林的存在。
So you have, like, six-degree increase in temperature and 50, 60, 80 percent of reduction in rainfall.
所以，气温会上升6度，而降雨会减少50%、60%、80%。
The forest wouldn't survive anymore.
森林再也活不下去了。
Even now the Amazon's trees appear to be absorbing less carbon dioxide than they used to.
即便是现在，亚马逊的树木吸收的二氧化碳似乎也比以前少了。
In 2015 the scientist Roel Brienen and scores of co-authors published a study showing that trees in intact Amazon forests absorbed 30 percent less carbon dioxide in the 2000s than they had in the 1990s.
2015年，科学家罗尔·布里宁和数十名合著者发表的一项研究表明，在本世纪头十年，未遭破坏的亚马逊森林里的树木吸收的二氧化碳比上世纪90年代减少了30%。
If these trends in the Amazon would continue, then obviously the carbon sink will shut down in a matter of one or two decades.
如果亚马逊森林的这种趋势继续保持下去，那么很明显，碳汇将在一二十年内消失。
And he told me that five years ago. That's fair to say.
五年前他就告诉我了。这么说是有道理的。
Roel is a geography professor at the University of Leeds.
罗尔是利兹大学的地理学教授。
His paper's worrisome conclusion was based on decades of painstaking measurements of thousands of trees in hundreds of plots throughout the Amazon basin.
他的论文给出了令人担忧的结论，是对亚马逊盆地里数百块土地上数千棵树进行了数十年的艰苦测量得出的。
He said that the study could not explain the decline's cause.
他说，这项研究无法解释碳吸收量下降的原因。
We do need to understand better what is causing these trends.
我们确实需要更好地了解是什么导致了下降趋势。
So that's the importance, in a nutshell, of doing this experiment.
简而言之，这就是做这个实验的重要性。
And so David and several Brazilian colleagues and a team of international collaborators laid out the two circular plots that I saw at ZF2.
大卫和几位巴西同事以及一个国际合作者团队展示了我在ZF2看到的两个圆形地块。
When we spoke in 2016, he was optimistic that soon they might know whether increased carbon dioxide will protect the Amazon.
2016年我们交谈的时候，他乐观地认为，他们可能很快就会知道增加二氧化碳能否保护亚马逊。
This experiment that has never been done in the tropics-in any tropical forest-it would be one of the most important scientific data to be collected in the tropical world.
这项从未在任何热带森林进行过的实验，将是热带雨林领域收集到的最重要的科学数据之一。
Most climate researchers believe that carbon fertilization explains why the Amazon is a sink today.
大多数气候研究人员认为，碳肥可以解释为什么如今的亚马逊是一个碳汇场所。
But there are many reasons why carbon fertilization might not keep the sink from failing tomorrow.
但是，碳肥并不能阻止碳汇在不远的未来崩溃，有很多原因。
For instance, Amazon soil might run out of the crucial nutrient phosphorus, blunting any benefit from extra carbon dioxide.
例如，亚马逊土壤可能会耗尽重要的营养磷，削弱额外的二氧化碳带来的任何好处。
Scott says that getting a grip on what makes the Amazon forest tick is essential for predicting the rate of global warming.
斯科特说，了解亚马逊森林的变化对于预测全球变暖速度至关重要。
This is actually right up there with our uncertainty about politics and economics and energy technology.
这实际上与我们对政治、经济和能源技术的不确定性有关。
That the behavior of forests, and especially tropical forests, has as much leverage on the future of climate change, as, let's say, economic development in India and Africa-I mean, it's huge.
森林的行为，尤其是热带森林，对气候变化的未来的影响力与印度和非洲的经济发展一样大--我的意思是，它的影响力是巨大的。
So huge stakes for the planet-and a possible answer to the scientific question critical to knowing how much carbon the forest will take in, or possibly release, in the future.
这对地球来说有巨大的利害关系--也可能解答森林未来将吸收或可能释放多少碳这个至关重要的科学问题。
