作者:Donella H. Meadows
幾個月前，聯合國決定規劃一個節日來宣佈地球人口將突破另一個十億。他們已經隨意選了一個日子－十月十二日，宣佈為六十億人日子。
這應該是怎麼樣的一個日子呢？是該懺悔的日子？還是值得慶祝的日子？在刺人的聲音世界裡，這該配什麼樣的音調呢？「六十億，嗚？」還是「六十億，耶？」
六十億的人，誰來算算這麼多的人呢？
我猜這一天是屬於「嗚」的，我們過去就是習慣於這樣地告訴我們自己，人口過剩，人口炸彈，人口爆炸，人口問題。沒有一個人可製造人口問題，是我們自己造成的，但是我們大部分的人似乎只能為此而唉嘆。
我十分明瞭這是為什麼，我們人口數的增加已經令人提心吊膽，而且越來越嚴重，平均每年成長七千八百萬人，相當於每六個月就新增加了一個墨西哥市(Mexico Ctiy)人口數。實際上人口都是在我們所謂的「發展中」的地方中增加。
在加薩的兒童，正在垃圾堆裡頭翻找東西(照片來源: 聯合國)
從地球的角度來看，我們確實看起來是像爆炸一般，在1800年時，我們只有十億人口，在1960年我們已經達到三十億人口，以地球的眼睛來看這不過是一眨眼的時間而已。現在我們第五十億個出生的人不過才十二歲，第四十億個出生的人也才二十五歲。
不只是我們的人口變多了而已，我們每一個人所使用的能源及物質、製造的污染及廢棄物而言，也都變大了。我們在地球表面蓋滿了燈光、建築物、農田、道路、飛機、船隻和垃圾場。我們甚至已經使臭氧層受到侵害並且正在改變我們的氣候。我們侵犯到了其他物種的生活空間，造成自恐龍滅絕以來，最大且最急劇性的物種滅絕。
蘇丹的村民們聚集在飛機空投糧食所行經的航道上，等著撿拾散落出來的糧食。攝影：Eskinder Debebe，取自聯合國。
但是就我們所知，我們是這個星球上第一個生物進化到可以了解有承載力(carrying capacity)這個東西，同時也知道超過這個承載力之後會有得到什麼懲罰。科學家們已經開始在計算我們的地球在什麼樣的生活水準之下可以承受多少的人口數，雖然確實的數字尚未有共識，但明顯的證據顯示我們早已超過這個數量了。
我們的漁業逐漸衰敗
一個由數千個科學家組成的聯盟呼籲我們必須減少60%至80%的石化燃料使用，才能讓穩定氣候變成有一點點希望。
我們的農人不能跟上人口數的成長，自1984年以來單位穀物產量便一直下降。
塞內加爾．龜裂的大地。攝影：Evan Schneider，取自聯合國
一些大河如科羅拉多河、黃河、尼羅河、恒河、印度河、昭披耶河、錫爾河及阿姆河等都因為灌溉或者城市的過度使用而快速消耗，造成河道在一年當中有幾個月或甚至終年乾凅。在印度、中國北部、加州中部的山谷及其它許多地方都在以一種不能夠在如此繼續的速率過度的抽取地下水。
世界森林委員會(The World Commission on Forests)表示「目前全球有一個非常明顯的趨勢，就是森林的面積持續地大量流失...，許多僅剩的森林也正持續地枯竭，而所有的森林都遭受到威脅。」
兩位英屬哥倫比亞大學研究員已經計算出我們的「生態足跡(ecological footprint)」，生態足跡的意義是指用來生產我們所需的資源及消化我們所產生廢物所需要的土地數量，他們說我們的生態足跡已經超過了地球上具有生產力的土地面積總量的20%，而唯一使我們尚可免受這過大衝擊的原因，就是還有森林、魚類、泥土及水等庫存資源可供給我們消耗。
加拿大的森林業．攝影： Sean O'Brien
我們不能再永無止盡地消耗下去，甚至再久一些也不行，我們沒有選擇的餘地，如果我們不能自動減輕對地球造成的負荷，地球會自己為人類來解決，到時候我們的人口問題就解決了。
當然，我們不一定要接受那樣的結局，有幾個徵兆顯示我們實際上是一個聰明的物種。目前的出生率已經開始下降了，1950年代平均一個婦女生下六個小孩，到了1990年代這個數字降到2.9個，富裕國家婦人生育率還低於人口替代率兩個小孩。一些國家的人口還是持續成長，像美國就受到外來移民及嬰兒潮的影響。但是如果生育力維持在現在的水準，歐洲的人口將會從1998年的七億兩千八百萬下降到2025年的七億一千五百萬。
受到可怕的六十億人口奇觀的啟發，我們可以決心以溫文地、逐漸地、不分區域地將人口數減少到二十億，這也許要花一到兩百年的時間，才能讓全人類有好的生活，也讓留給地球很多的自然環境空間。
人口數到達二十億的那一天，才是值得慶祝的一天。
要達到那樣的境界，我們不能把自己，貧窮者，尤其是那許多小孩的貧窮母親當成是地球的癌症。相反的，泰國、哥斯大黎加、印尼等國的人口出生率得以下降，是因為給予這些貧窮可憐的婦女更多的權力及讓她們更富裕。不論是哪個地方，只要是教育、健康照料、合適的工作、家庭計畫等能夠慷慨的廣泛地提供服務，家庭人數就會變少。
越南．母親與小孩．取自聯合國
除此之外，我們的消費量也需要降低，人口數目不是讓地球變差的因素，真正的原因是人口數乘上每個人所使用的能量及物質量的結果。美國的生態足跡平均比印度要大上十三倍，美國今年出生的四百萬個嬰兒，將對地球造成的衝擊要比印度的兩千六百萬個嬰兒大上兩倍。
如果你知道該到哪裡去看的話，你會了解降低地球的負擔，也會帶來更好的生活，從事有機農業的人可在不使用化學藥品的情形下，生產高的健康食物產量。綠建築師能設計出每平方英尺使用不到原來能源一半的建築物而且讓人更舒服呢。點滴灌溉能使用較少的水而有較高的產量。風車、太陽能收集器及燃料電池能在不破壞氣候的其況下產生電力。最好的事是，許多人正從廣告的洗腦過程中釋放出來，知道他們已經擁有足夠的物品。
美麗的地球，取自NASA
不管媒體會針對達到六十億人的這一天作什麼，我想我們是真正的一家人，每一個人都像是大海中的一小滴水，因此不要將自己簡單化或平庸化，不要互相諷刺，描繪成地球的災難或是征服者，也不要絕望或是歡欣慶祝。我們知道我們對人類與同住有限星球上的其他數百萬種生物所製造的問題，我們知道支持六十億人口這項成就是包含許多的不族與不公平。我希望的是我們能夠更尊敬彼此、互相鼓勵、互相幫助，為每個人富有的願望而努力、為了讓這個世界能成為多樣的、充足的、公平的、歡喜的、可持續的、有豐富自然的世界而奉獻己力。
不管有多少十億人，如果每個一人，都能變成如此！就能改變！
唐內拉麥道斯是永續研究所所長暨達特茅斯學院環境研究教授
版權歸屬 Earth Day Network，環境信託協會 (陳均輝 譯，梁明煌審校)
Donella H. Meadows
Months ago, the United Nations decided to make an event out of the fact that the human population meter would soon click over another billion. They picked an arbitrary date -- October 12 -- and declared it the Day of 6 Billion.
What kind of event should this be? A day of repentance? A celebration? In a world of soundbites, what's the right tone here? Six billion, oh woe? Six billion, yippee?
My guess is that "oh woe" will rule the day. That's how we're used to talking about ourselves. Overpopulation, population bomb, population explosion, the population problem. Nobody is doing this population thing to us; we are doing it to ourselves. But most of us seem to lament it.
I can surely understand why. Our numbers are scary and getting scarier. We are growing at 78 million per year, the equivalent of a new Mexico City every six months. Virtually all that growth is happening in places we call "developing."
From the point of view of the planet, we must indeed look like an explosion. In 1800 there were just 1 billion of us. We hit 3 billion in 1960 and have doubled again in the blink of a planetary eye. Our 5 billionth person is now just 12 years old; our 4 billionth is just 25.Not only are there so many more of us, but each of us is bigger, as measured by the energy and material we use and the pollutants and wastes we spew out. We cover the globe with our lights and buildings and farms and roads and planes and ships and dumps. We have eaten into the ozone layer and are changing the climate. We're moving into the space of other species, causing an extinction spasm greater than anything the earth has seen since the fall of the dinosaurs.
But we are, as far as we know, the first creatures on this planet evolved enough to realize that there is such a thing as a carrying capacity and that there are penalties for exceeding it. Our scientists have begun to calculate how many of us at what standard of living the earth can support. They don't agree on an exact number, but there's clear evidence that we're already beyond it.
Our fisheries are crashing.
A coalition of thousands of scientists says we must cut back our fossil fuel burning by 60 to 80 percent to have any hope of stabilizing our climate.
Our farmers are not keeping up with our population; grain output per capita has been falling since 1984.Huge rivers -- the Colorado, Yellow, Nile, Ganges, Indus, Chao Phraya, Syr Darya, and Amu Darya -- are so drained by irrigation and cities that their channels run dry for some or all of the year. In India, North China, California's Central Valley, and many other places, we are pumping down groundwater at rates that cannot continue.
The World Commission on Forests says, "There has been a clear global trend toward a massive loss of forested areas. ... Much of the forest that remains is being progressively impoverished and all is threatened."
Two researchers at the University of British Columbia have calculated our "ecological footprint" -- the amount of land needed to produce our resources and absorb our wastes. They say our footprint is now 20 percent greater than the productive land base of the planet. The only reason we can get away with that over big impact is there are still stocks of forest, fish, soils and waters to draw down.
We can't go on drawing down forever, or even much longer. We don't get a choice about that. If we don't reduce our load on the planet voluntarily, the planet will do it for us. That will solve our population problem.
Of course we don't have to submit to that outcome. There are signs that we are in fact an intelligent species. Birth rates are coming down. In the 1950s the average woman bore six children; in the 1990s that number fell to 2.9. In every rich nation the fertility rate is below the replacement rate of two children per woman. Some, such as the United States, are still growing because of immigration and/or baby-boom cohorts moving through their reproductive years. But if fertility holds at present levels, the population of Europe will decline from 728 million in 1998 to 715 million in 2025.We could, inspired by the awesome spectacle of our 6 billion, choose to bring our numbers down gracefully, gradually, everywhere, over a century or 2, to around two billion, which would allow good lives for all humans and leave plenty of room for nature as well.
The Day of 2 Billion! That would be worth celebrating!
To get there, we need not regard ourselves, especially not the poor among us, especially not the poor mothers of many children, as a cancer upon the earth. Quite the contrary. What is bringing down birth rates in Thailand, in Costa Rica, in Malaysia, is the empowerment and enrichment of poor women. Education, health care, decent jobs, family planning programs, wherever these are generously available, family sizes come down.
The other thing that has to come down is consumption. The number of people is not what degrades the earth; it's the number of people times the flow of energy and material each person commands. The ecological footprint of the average American is 13 times that of the average Indian. The 4 million babies born in the U.S. this year will have twice the earthly impact of the 26 million babies born in India.
If you know where to look, you can see how good lives can be lived with much less load on the planet. Organic farmers produce high yields of healthy foods without chemicals. "Green" architects design buildings that use less than half the energy per square foot and are more comfortable. Drip irrigation grows crops with higher yields using less water. Windmills and solar collectors and fuel cells produce power without crazing the climate. Best of all, many people are freeing themselves from the steady brainwashing of the advertisers and deciding that they actually have enough.
Whatever the media do with the Day of 6 Billion, I'd suggest that we real folks, each of us an infinitesimal drop in that huge sea, refuse to simplify or trivialize it, refuse to caricature each other as either the scourges or the conquerors of the earth, refuse either to despair or to rejoice. We know of the problems we cause each other and the millions of other creatures that co-inhabit our finite planet. We know of the accomplishments we've pulled off just to be able to support six billion of us, however inadequately or inequitably. What I hope we will have the greatness to do is respect each other, encourage each other, reach out to each other, commit to the vision of everyone being able to thrive and contribute to a diverse, sufficient, equitable, joyful, sustainable, nature-rich world.
Everyone -- however many billion that turns out to be.
Donella H. Meadows is director of the Sustainability Institute and an adjunct professor of environmental studies at Dartmouth College.
