【聯合報／By EDUARDO PORTER／馮克芸譯】
Forecast of Famine May Come True
Might Thomas Malthus be vindicated in the end?
About 10 years after a hungry, angry populace had ushered in the French Revolution in 1789, Malthus predicted that exponential population growth would condemn humanity to the edge of subsistence.
“The power of population is so superior to the power in the earth to produce subsistence for man, that premature death must in some shape or other visit the human race,” he wrote with alarm.
This was, we now know, wrong. The gloomy forecast was soon buried under an avalanche of progress that spread from England around the world. Between 1820 and 2000 the world’s population grew sixfold. Economic output multiplied by more than 50.
Nonetheless, Malthus’s prediction was based on an eminently sensible premise: that the earth’s carrying capacity has a limit. On March 31, the United Nations Intergovernmental Panel on Climate Change provided a sharp warning about how fast we are approaching this constraint.
“In many cases, we are not prepared for the climate-related risks that we already face,” said Vicente Barros, co-chairman of the panel and professor emeritus of climatology at the University of Buenos Aires.
The list of present damages outlined by the United Nations panel — melting ice caps and rising sea levels, stressed water supplies, heat waves and heavy rains — underscored the risk if humanity does not figure out how to curb the use of fossil fuels.
The report provides the starkest warning yet about the challenge imposed by global warming on the food supply. And it is pessimistic about the prospect of extra grain production in temperate zones, where more carbon dioxide in the atmosphere would increase the rate of photosynthesis, raising yields, and warmer weather would lengthen the growing season.
Faster photosynthesis will help weeds more than cereal crops, while the accumulation of ozone and high temperatures would reduce yields of the major grains, according to the report.
This would be bad enough if demand for food were to remain constant. It won’t. Studies suggest that feeding more than nine billion people in 2050 will require 70 percent more calories than the world’s population consumes today, according to Craig Hanson, director of food, forests and water programs at the World Resources Institute.
Indeed, the panel calculates that food demand is rising 14 percent per decade. But it estimates that climate change is already reducing wheat yields by 2 percent each decade and corn yields by 1 percent.
“This is a wake-up call for the agriculture sector,” Mr. Hanson said. “Climate change is a food security issue. It’s not just an environmental issue.”
The climate panel’s findings do not quite endorse the Malthusian idea that famine will spread practically everywhere. But a world with a more unstable food supply is likely to be a more volatile place. And those most exposed will be the world’s poor.
“There is a rigorous correlation between food price spikes and urban unrest,” said Andrew Holland, who studies climate change at the American Security Project, a research group in Washington. “There was a food price spike in 2008, and you can see unrest spread throughout Africa. And there’s a relatively clear line that leads from the food price spike in 2010 to unrest in the Middle East and the Arab Spring.”
Still, there are reasons to take prophesies of doom with skepticism. Humanity has a capacity to invent ways around constraints, using resources more efficiently and switching from scarcer commodities to more abundant ones.
Indeed, the climate panel suggests a variety of ways in which countries could adapt to a changing climate. Farmers could breed new species to better resist heat and drought. Water harvesting techniques could be used to delay evaporation. Rotation of crops could help improve yields.
Changes in demand and logistics could also help cope with scarcer food. Mr. Hanson pointed out that one-quarter of the food produced in the world today is wasted — by either poor storage and transport infrastructure in developing countries or wasteful consumers in the rich world.
But for all the evidence of humankind’s ability to adapt to its environmental constraints, it would be reckless to assume that ingenuity will arrive just in time to pull us from the brink.
中譯
事實最終會證明人口學家馬爾薩斯是對的嗎？
憤怒又飢餓的平民1789年迎來了法國大革命，約10年後，馬爾薩斯預測，人口等比級數成長將把人類逼到存活的邊緣。他撰文警告：「人口的力量遠超過地球供養的力量，死於非命之事必會以某種形式降臨人類。」
現在我們知道他錯了。那悲觀的預測很快就被一段從英格蘭擴及全世界、沛然莫之能禦的成長進步所掩埋了。從1820年到2000年，世界人口增加了5倍，經濟產出卻增加了50倍以上。
然而馬爾薩斯的預測根據的是極為合理的前提：地球的承載能力有其極限。今年3月31日，聯合國政府間氣候變遷委員會提出了我們正快速接近這個極限的嚴正警告。
該委員會共同主席、布宜諾斯艾利斯大學氣候學榮譽教授巴洛斯說：「在許多方面，我們已面臨與氣候相關的風險，卻尚未做好準備。」
該委員會列出我們目前的災害：極地冰融、海平面上升、供水吃緊、熱浪及暴雨頻仍，凸顯了人類如不設法少用化石燃料，有多危險。
報告針對全球暖化在糧食供應上形成的挑戰，提出迄今最直白的警告。報告對溫帶地區穀物增產也表示悲觀，溫帶大氣中二氧化碳增多會促進植物光合作用速率、提高產量，而天氣變暖也會使生長季變長。
報告中說，光合作用加快對雜草的助益大於對穀物，臭氧的累積及高溫將使主要穀物的收成減少。
即使人類的糧食需求能維持穩定，這都夠糟了，更何況情況並非如此。世界資源研究所糧食、森林及水計畫主任韓森的多項研究指出，在2050年要養活90億以上人口，所需食物熱量將比現今全球人口之消耗量多70%。
聯合國委員會甚至計算出糧食需求每10年會增加14%，但估計氣候變遷正使小麥及玉米產量每10年各減少2%及1%。
韓森說：「這對農業部門是一記醒鐘。氣候變遷不只是環境問題，還是糧食安全保障問題。」
聯合國委員會的結論並不完全贊同馬爾薩斯派幾乎全球都將出現飢荒的概念。但一個糧食供應較不穩定的世界，很可能也會擾攘不安。而受害最深的將是這世上的窮人。
華府智庫「美國安全計畫」研究氣候變遷的歐蘭德說：「糧價上漲和都市動盪息息相關。2008年曾出現糧價上漲，你可以看到當年動盪席捲了整個非洲。而從2010年糧價上漲到中東動盪及阿拉伯之春運動之間，有一條相當明顯的導線。」
然而我們仍有理由對這種悲觀的預言表示懷疑，因為人類有能力在諸多限制之下，藉由更有效率使用資源、捨較稀有商品改用產量較多的商品，闖出一條路。
氣候委員會明確提出多種建議，供各國因應氣候變遷。農民可培育更能抗旱抗高溫的新品種，集水技術可用來延緩蒸發，輪植則可提高作物產量。
需求及物流的改變也有助於因應糧食短缺。韓森指出，現今全世界生產的食物有四分之一蹧蹋掉了，原因可能是開發中國家貯存及運輸的基礎設施差勁，或是讓富裕國家的揮霍消費者給浪費掉了。
但儘管人類總有能力適應環境限制，若認定巧智靈心將及時出現，救人類於絕境邊緣，那可就太不負責任了。
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