亞馬孫森林砍伐與全球乾旱 Deforestation and Drought

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 rationed in S漀 Paulo, a megacity of 20 million people; in Rio; and in many other places.

和加州一樣，巴西的大部分地區遭受了有史以來最嚴重的一次旱災。巨大的水庫完全乾涸，在擁有兩千萬人口的巨型城市聖保羅以及里約熱內盧等地，供水開始實行定量配給。

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.

乾旱通常被看做是自然災害，超出人類的控制範圍。但是通過深入探究地球不斷變化的生物氣候——生物和氣候力量之間巨大複雜的全球性相互作用——研究者們現在可以認識到，砍伐森林在其中扮演着關鍵角色。

Cutting down forests releases stored carbon dioxide, which traps heat and contributes to atmospheric warming. But forests also affect climate in other ways, by absorbing more solar energy than grasslands, for example, or releasing vast amounts of water vapor. 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 dynamics are not well understood.

砍伐會釋放森林儲存的二氧化碳，二氧化碳吸收熱量導致大氣增溫。但是森林也會以其他方式影響氣候，比如說，通過比草原吸收更多的太陽能，或是通過釋放大量水蒸氣等方式。許多專家認爲，如此大規模的森林砍伐，特別是在南美洲，已經顯著地改變了世界氣候——儘管人們還沒能很好的理解其動態。

“A lot of people are scrambling 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.”

“由於預計大厄爾尼諾現象的到來，很多人今年都爭着到亞馬孫進行觀察，”華盛頓大學的生態氣候學家阿比蓋爾·L·S·斯萬(Abigail L. S. Swann)說，“厄爾尼諾現象預計將導致亞馬孫地區明顯的乾旱，這將改變可以供應林木的水量。”

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 transpire 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.

人類很早就定居在降水充足且穩定的地方，大片森林在產生穩定降雨量過程中起到關鍵作用。樹木可以吸收土壤中的水分並將之蒸發，使水分進入大氣層。一棵成年的樹，一天能將1000升的水蒸氣釋放到大氣中：整個亞馬孫雨林每天釋放200億噸之多。

The water vapor creates clouds, which are seeded with volatile 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.

水蒸氣形成雲，雲中帶着樹木自然散發的萜烯和異戊二烯這樣的揮發性氣體，可以形成雨。這些富含水量的雲隨風移動很長的距離，形成一條降水傳送帶，科學家稱之爲“飛翔的河流”。

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 westward over the emerald crown of the Amazon, where it picks up far more moisture. The laden clouds eventually bump up against the Andes and are steered south and then east, which means rain for Bolivia and Brazil.

亞馬孫上空的“河”比亞馬孫河本身的水還多。它開始是聚集在大西洋上空的溼氣，然後向西掠過亞馬孫的“翡翠冠”雨林，在那裏吸收大量的水分。滿載的雲層最終撞上了安第斯山脈，並轉向南部然後向東，這就形成了玻利維亞和巴西的降雨。

One way forests may move water is known as “biotic pumping.” As water transpires 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, essentially turning off the pump. Large-scale deforestation is thus believed to be a major contributor to the extreme drought in Brazil.

森林轉移水的一種方式被稱爲“生物泵”。該理論認爲，水蒸發到森林上空的大氣中，創造了一個低壓系統，吸入周圍空氣，最終不斷將溼氣送入內陸。砍伐森林會減弱這些低壓系統，基本上關閉這個”泵“。大規模森林砍伐因此被認爲是巴西極端乾旱的主要原因。

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.

科學家們很早就知道了植被對天氣的深遠影響。1907年，官員們建造了一個橫貫澳大利亞、長達2000英里的籬笆，用來阻止內陸具有破壞性的兔子進入農田。有原生植被的一邊，天空中形成了雨雲，但農田上空卻是晴朗的。“兔子圍欄實驗”顯示開墾的一邊降雨量下降了20%。研究人員仍在試圖解釋爲什麼，但主要理論是，顏色較深的原生植物吸收更多的熱量，並釋放到大氣中，隨熱量一起釋放的還有用來形成雲的能量和水蒸氣。

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 emissions and absorption of the sun’s energy.

如今研究人員主要依靠計算機建模來了解森林砍伐的影響，這是一項艱鉅的任務，因爲樹木控制氣候的途徑多且複雜，包括降水、碳儲存、大片雲團複雜的化學釋放以及對太陽能量的吸收等。

“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.”

“這是一個邊緣領域，”美國航空航天局噴氣推進實驗室(Jet Propulsion Laboratory)的生態氣候學家、《氣候和生態系統》(Climate and Ecosystems)一書的作者大衛·希米爾(David Schimel)說。“但主要是因爲這個領域很困難，而不是因爲無人關注。”

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.

僅僅在過去一年，亞馬孫河地區就有約2000平方英里（約合5180平方公里）的森林遭到砍伐，面積和一個特拉華州相當，土地被用以種植大豆和飼養牛羣。越來越多的科學家警告稱，大規模的濫砍濫伐——亞馬孫地區有20%左右的森林已經消失，另有約同等面積的森林逐步退化——可能已經產生影響，使一直以來有充足降水地區的雨水向別處轉移。

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 uncertainty embedded 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 robust notion.”

普林斯頓大學的一份研究顯示，砍伐亞馬孫森林可能導致遠至加利福利亞州等地的乾旱；而其他研究表明，最近德克薩斯州和新墨西哥州發生的乾旱可能和亞馬孫地區的濫砍濫伐有關。儘管這類研究存在固有的不確定性，但“大量證據顯示，改變亞馬孫河地區的水循環會導致全球性的後果，”希米爾說，“這是一個相當紮實的見解。”

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 abrupt large-scale shift to grasslands, which could substantially alter global weather patterns “and cause a breakdown of the current climate system.” If deforestation continues, he has said, S漀 Paulo will most likely “dry up.”

而且，其影響可能會加速呈現。在近期的一份報告中，安東尼奧·多納託·諾步雷(Antonio Donato Nobre)警告說，如果亞馬孫地區被砍伐的森林達到40%，該區可能突然出現大片區域退化爲草地的情況，這可能給全球的天氣規律造成巨大改變，“並使得現在的氣候系統崩潰。”諾佈雷和巴西國家空間研究所(National Institute for Space Research)合作，常年從事氣候學研究。他還說，如果濫砍濫伐持續下去，聖保羅極有可能“乾涸”。

In the broadest sense, scientists say, forests represent a kind of ecological infrastructure 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 stabilizing soil — or, in this case, by regulating climate.

科學家說，從最廣泛的意義上來說，森林代表了一種生態基礎設施，它們吸收和控制二氧化碳，其樹根能淨化水質，並可以鞏固土壤，或者像本文中提到的這樣，對氣候進行調節，從而避免洪水，幫助維持地球的舒適生存環境，

Dr. Nobre and other climate experts are urging an immediate 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 stabilize its pivotal role in climate.

諾佈雷和其他氣候學家正在呼籲人們立即停止砍伐森林，以及通過大規模再植森林，使亞馬孫河地區恢復到健康狀態，使其在氣候中的重要作用穩定下來。

Gordon Bonan, a scientist at the University Corporation for Atmospheric Research in Boulder, 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)是一名就職於科羅拉多州博爾德的美國大學大氣研究聯合會(University Corporation for Atmospheric Research)的科學家，出版過《生態氣候學》(Ecological Climatology)一書。他認爲應當把減少濫砍濫伐和進行森林再植作爲第一要務，這不僅是對巴西而言，對整個北美都是如此。氣候系統的健康是衆多的原因之一。“變化的速度已遠遠超過我們對變化本身的理解，”他說，“而等到我們真正理解的時候，很可能爲時已晚。”

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.

誠然，大量植樹造林會大規模地改變地下水的流向，而且比無植被地區吸收更多養分，這可能產生複雜甚至負面的影響。“總體而言，”如果處理恰當的話，“這是應對氣候變化的積極措施，”他接着說。

Some people aren’t waiting for further research and are hoping to geoengineer local climates with new forests. Bishop 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 glaciers. During that time, he estimates, they have planted 3.7 million trees.

有的人已經不再等待更多的研究，而希望通過再植森林人爲改造當地氣候。坦桑尼亞福音信義會(Evangelical Lutheran Church)的當選主教弗雷德裏克·休(Fredrick Shoo)已經和10萬教民沿乞力馬扎羅山植樹12年，吹經此地的風熾熱而乾燥，會融化山上的冰川，他們希望此舉能降低風的溫度。他估計在這段時間裏，他們大概種植了370萬棵樹。

“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.”

“我希望我們能恢復乞力馬紮羅的森林，並保護這裏的水源，”人稱“樹主教”的休說，“我們有保護天地萬物的道德義務，並保證子孫後代有一個良好的生存空間。”