亚马孙森林砍伐与全球干旱

LIKE California, much of Brazil is gripped by one of the worst droughts in its history. Huge reservoirs are bone dry and water has been rationed¹ in S漀 Paulo, a megacity of 20 million people; in Rio; and in many other places.

和加州一样，巴西的大部分地区遭受了有史以来最严重的一次旱灾。巨大的水库完全干涸，在拥有两千万人口的巨型城市圣保罗以及里约热内卢等地，供水开始实行定量配给。

Drought is usually thought of as a natural disaster beyond human control. But as researchers peer deeper into the Earth’s changing bioclimate — the vastly complex global interplay between living organisms and climatic forces — they are better appreciating the crucial role that deforestation plays.

干旱通常被看做是自然灾害，超出人类的控制范围。但是通过深入探究地球不断变化的生物气候——生物和气候力量之间巨大复杂的全球性相互作用——研究者们现在可以认识到，砍伐森林在其中扮演着关键角色。

Cutting down forests releases stored carbon dioxide, which traps heat and contributes to atmospheric² warming. But forests also affect climate in other ways, by absorbing more solar energy than grasslands³, for example, or releasing vast amounts of water vapor⁴. Many experts believe that deforestation is taking place on such a large scale, especially in South America, that it has already significantly altered the world’s climate — even though its dynamics⁵ are not well understood.

砍伐会释放森林储存的二氧化碳，二氧化碳吸收热量导致大气增温。但是森林也会以其他方式影响气候，比如说，通过比草原吸收更多的太阳能，或是通过释放大量水蒸气等方式。许多专家认为，如此大规模的森林砍伐，特别是在南美洲，已经显著地改变了世界气候——尽管人们还没能很好的理解其动态。

“A lot of people are scrambling⁶ to make observations in the Amazon this year, with the expected big El Ni漀 coming,” said Abigail L. S. Swann, an eco-climatologist at the University of Washington. “It’s expected to drive significant drought over the Amazon, which will change how much water trees have available.”

“由于预计大厄尔尼诺现象的到来，很多人今年都争着到亚马孙进行观察，”华盛顿大学的生态气候学家阿比盖尔·L·S·斯万(Abigail L. S. Swann)说，“厄尔尼诺现象预计将导致亚马孙地区明显的干旱，这将改变可以供应林木的水量。”

Humans have long settled in places where there is adequate and predictable precipitation, and large forests play a crucial role in generating dependable amounts of rainfall. Trees take up moisture from the soil and transpire⁷ it, lifting it into the atmosphere. A fully grown tree releases 1,000 liters of water vapor a day into the atmosphere: The entire Amazon rain forest sends up 20 billion tons a day.

人类很早就定居在降水充足且稳定的地方，大片森林在产生稳定降雨量过程中起到关键作用。树木可以吸收土壤中的水分并将之蒸发，使水分进入大气层。一棵成年的树，一天能将1000升的水蒸气释放到大气中：整个亚马孙雨林每天释放200亿吨之多。

The water vapor creates clouds, which are seeded with volatile⁸ gases like terpenes and isoprene, emitted by the trees naturally, to form rain. These water-rich banks of clouds travel long, wind-driven distances, a conveyor belt for the delivery of precipitation that scientists call flying rivers.

水蒸气形成云，云中带着树木自然散发的萜烯和异戊二烯这样的挥发性气体，可以形成雨。这些富含水量的云随风移动很长的距离，形成一条降水传送带，科学家称之为“飞翔的河流”。

The sky-borne river over the Amazon carries more water than the Amazon River itself. It begins as moisture that builds over the Atlantic Ocean, and then flows westward⁹ over the emerald crown of the Amazon, where it picks up far more moisture. The laden¹⁰ clouds eventually bump up against the Andes and are steered¹¹ south and then east, which means rain for Bolivia and Brazil.

亚马孙上空的“河”比亚马孙河本身的水还多。它开始是聚集在大西洋上空的湿气，然后向西掠过亚马孙的“翡翠冠”雨林，在那里吸收大量的水分。满载的云层最终撞上了安第斯山脉，并转向南部然后向东，这就形成了玻利维亚和巴西的降雨。

One way forests may move water is known as “biotic pumping.” As water transpires¹² into the atmosphere above the forest, the theory holds, it creates a low-pressure system that sucks in air surrounding it, eventually and continually pumping moisture inland from the ocean. Cutting down forests degrades these low-pressure systems, essentially¹³ turning off the pump. Large-scale deforestation is thus believed to be a major contributor to the extreme drought in Brazil.

森林转移水的一种方式被称为“生物泵”。该理论认为，水蒸发到森林上空的大气中，创造了一个低压系统，吸入周围空气，最终不断将湿气送入内陆。砍伐森林会减弱这些低压系统，基本上关闭这个”泵“。大规模森林砍伐因此被认为是巴西极端干旱的主要原因。

Scientists have long known that vegetation has a profound effect on weather. In 1907, officials built a 2,000-mile-long fence across Australia to keep invasive rabbits from crossing from the wild outback into farms. On the side with native vegetation, rain clouds formed in the sky above, but the farm-field skies were clear. The “bunny-fence experiments” charted a decline in rainfall of 20 percent on the cultivated side. Researchers are still trying to explain why, but the leading theory is that the darker native plants absorb more heat and release it into the atmosphere, along with energy and water vapor to form clouds.

科学家们很早就知道了植被对天气的深远影响。1907年，官员们建造了一个横贯澳大利亚、长达2000英里的篱笆，用来阻止内陆具有破坏性的兔子进入农田。有原生植被的一边，天空中形成了雨云，但农田上空却是晴朗的。“兔子围栏实验”显示开垦的一边降雨量下降了20%。研究人员仍在试图解释为什么，但主要理论是，颜色较深的原生植物吸收更多的热量，并释放到大气中，随热量一起释放的还有用来形成云的能量和水蒸气。

Today’s researchers mainly rely on computer modeling to understand the effects of deforestation, a difficult task because there are so many complex pathways through which trees control climate: precipitation, carbon storage, large clouds of complex chemical emissions¹⁴ and absorption of the sun’s energy.

如今研究人员主要依靠计算机建模来了解森林砍伐的影响，这是一项艰巨的任务，因为树木控制气候的途径多且复杂，包括降水、碳储存、大片云团复杂的化学释放以及对太阳能量的吸收等。

“This area is a frontier,” said David Schimel, an eco-climatologist at NASA’s Jet Propulsion Laboratory and the author of “Climate and Ecosystems,” “but a frontier because it’s difficult, not because it’s neglected.”

“这是一个边缘领域，”美国航空航天局喷气推进实验室(Jet Propulsion Laboratory)的生态气候学家、《气候和生态系统》(Climate and Ecosystems)一书的作者大卫·希米尔(David Schimel)说。“但主要是因为这个领域很困难，而不是因为无人关注。”

In the last year alone some 2,000 square miles of the Amazon — roughly the size of Delaware — were lost to clearing, largely for planting soybeans and raising cattle. A growing number of scientists are warning that wide-scale deforestation — about 20 percent of the Amazon forest is gone already and nearly that much is degraded — may already be directing precipitation away from places long accustomed to it.

仅仅在过去一年，亚马孙河地区就有约2000平方英里（约合5180平方公里）的森林遭到砍伐，面积和一个特拉华州相当，土地被用以种植大豆和饲养牛群。越来越多的科学家警告称，大规模的滥砍滥伐——亚马孙地区有20%左右的森林已经消失，另有约同等面积的森林逐步退化——可能已经产生影响，使一直以来有充足降水地区的雨水向别处转移。

One Princeton study suggested that deforesting the Amazon could potentially contribute to drought in places as far away as California, while other research indicated that recent droughts in Texas and New Mexico might be linked to cutting in the Amazon. Despite the uncertainty¹⁵ embedded¹⁶ in these and other studies, “There’s lots of evidence that changing the water cycle in the Amazon would have global consequences,” Dr. Schimel said. “It’s a fairly robust¹⁷ notion.”

普林斯顿大学的一份研究显示，砍伐亚马孙森林可能导致远至加利福利亚州等地的干旱；而其他研究表明，最近德克萨斯州和新墨西哥州发生的干旱可能和亚马孙地区的滥砍滥伐有关。尽管这类研究存在固有的不确定性，但“大量证据显示，改变亚马孙河地区的水循环会导致全球性的后果，”希米尔说，“这是一个相当扎实的见解。”

AND its impact could potentially accelerate. In a recent report, Antonio Donato Nobre, a veteran climatologist with Brazil’s National Institute for Space Research, warned that if just 40 percent of the Amazon region is deforested there could be an abrupt¹⁸ large-scale shift to grasslands, which could substantially alter global weather patterns “and cause a breakdown¹⁹ of the current climate system.” If deforestation continues, he has said, S漀 Paulo will most likely “dry up.”

而且，其影响可能会加速呈现。在近期的一份报告中，安东尼奥·多纳托·诺步雷(Antonio Donato Nobre)警告说，如果亚马孙地区被砍伐的森林达到40%，该区可能突然出现大片区域退化为草地的情况，这可能给全球的天气规律造成巨大改变，“并使得现在的气候系统崩溃。”诺布雷和巴西国家空间研究所(National Institute for Space Research)合作，常年从事气候学研究。他还说，如果滥砍滥伐持续下去，圣保罗极有可能“干涸”。

In the broadest sense, scientists say, forests represent a kind of ecological²⁰ infrastructure²¹ that helps maintain comfortable living conditions on the planet, whether by taking up and holding carbon dioxide, cleaning water through their roots, preventing floods by stabilizing²² soil — or, in this case, by regulating climate.

科学家说，从最广泛的意义上来说，森林代表了一种生态基础设施，它们吸收和控制二氧化碳，其树根能净化水质，并可以巩固土壤，或者像本文中提到的这样，对气候进行调节，从而避免洪水，帮助维持地球的舒适生存环境，

Dr. Nobre and other climate experts are urging an immediate²³ halt to deforestation, as well as large-scale planting of new forests, as a way to essentially nurse the Amazon back to full health and stabilize²⁴ its pivotal role in climate.

诺布雷和其他气候学家正在呼吁人们立即停止砍伐森林，以及通过大规模再植森林，使亚马孙河地区恢复到健康状态，使其在气候中的重要作用稳定下来。

Gordon Bonan, a scientist at the University Corporation for Atmospheric Research in Boulder²⁵, Colo., and the author of “Ecological Climatology,” said reducing deforestation and replanting forests should be priorities not just in Brazil but in North America and beyond for many reasons, including the health of climate systems. “The pace of change is far outpacing our understanding of what the change is doing,” he said, “and by the time we do understand it’s probably going to be too late.”

戈登·伯南(Gordon Bonan)是一名就职于科罗拉多州博尔德的美国大学大气研究联合会(University Corporation for Atmospheric Research)的科学家，出版过《生态气候学》(Ecological Climatology)一书。他认为应当把减少滥砍滥伐和进行森林再植作为第一要务，这不仅是对巴西而言，对整个北美都是如此。气候系统的健康是众多的原因之一。“变化的速度已远远超过我们对变化本身的理解，”他说，“而等到我们真正理解的时候，很可能为时已晚。”

While it is true that vast tree planting, which reroutes groundwater on a huge scale and absorbs far more energy than an unforested landscape, can have complex and potentially negative effects, “On balance,” if done properly, “it’s a positive strategy for climate change,” he added.

诚然，大量植树造林会大规模地改变地下水的流向，而且比无植被地区吸收更多养分，这可能产生复杂甚至负面的影响。“总体而言，”如果处理恰当的话，“这是应对气候变化的积极措施，”他接着说。

Some people aren’t waiting for further research and are hoping to geoengineer local climates with new forests. Bishop²⁶ Fredrick Shoo, the bishop elect of the Evangelical Lutheran Church in Tanzania, has been planting trees with 100,000 of his parishioners upwind of Mount Kilimanjaro for 12 years, in hopes of cooling the hot, dry winds that are melting the mountain’s glaciers²⁷. During that time, he estimates, they have planted 3.7 million trees.

有的人已经不再等待更多的研究，而希望通过再植森林人为改造当地气候。坦桑尼亚福音信义会(Evangelical Lutheran Church)的当选主教弗雷德里克·休(Fredrick Shoo)已经和10万教民沿乞力马扎罗山植树12年，吹经此地的风炽热而干燥，会融化山上的冰川，他们希望此举能降低风的温度。他估计在这段时间里，他们大概种植了370万棵树。

“My hope is we’ll be able to restore the forests of Kilimanjaro and save the water sources of Kilimanjaro,” said Bishop Shoo, known as the tree bishop. “We have a moral obligation to take care of creation and to be sure coming generations have a good place to live.”

“我希望我们能恢复乞力马扎罗的森林，并保护这里的水源，”人称“树主教”的休说，“我们有保护天地万物的道德义务，并保证子孙后代有一个良好的生存空间。”