全球暖化、降雨減少，天文台長有感而發，呼籲港人以少菜多肉支持環保，因為生產一公斤的牛肉需要消耗一萬五千公升水，是生產一公斤菜的七倍多。
這種比較，就像比較一公斤黃金跟一公斤水的價錢一樣，存在很大的謬誤。先把口味取向放在一邊，食物的基本作用是為人類提供能量。因此，菜與肉何者更加環保，不應只看生產相同重量的菜與肉的用水量，而是應該視乎透過兩者產生相同能量的的所需用水。
菜肉的種類繁多，根據食物安全中心的資料，一公斤的葉菜約提供一萬至三萬卡路里，而牛肉則大約是二十萬至三十萬卡路里。換句話說，吃菜所得的能量用水比率約為五至十五倍、吃肉則為十三至二十倍，吃肉能夠節省用水的機會似乎還要較大。
當然，以上是一個簡化的計算，變數很多。不過，至少我們應該明白，環保的方法需要更為嚴謹的思考計算，不能使之流於民粹口號。不然，只會適得其反。
4 則留言:
In the book "Superfreakonomics", Levitt and Dubner mention people should eat less red meat and dairy products because cows produce much greenhouse gas--methane.
So does this reason support the slogan "more veg. less meat"?
Cows fart and that produces methane because they are herbivores (plant eating). We human can switch from consuming meat to vegetable (plant also). But don't we fart too like the cows?
That's why Levitt and Dubner doesn't say we human should eat more vegetable.
I hope to make myself clear that I don't oppose to the needs of environmental protection. It is very clear in economics that we have the problem of externalities, which probably lead to the over-consumption of those public environmental resources.
What I want to point out here is that we need more serious methodology in protecting our environment. Cows may be good or bad to the environment, but the logic of the director is clearly wrong. Such trend in promoting environmental protection could do more harm than good.
張貼留言