This argument never quite makes sense to children. We all wondered, "How will my eating these peas help someone in Bangladesh? If I eat these peas, other peas won't magically be transported to south Asia."
However, your parents were right. (Of course your parents were right.) But their reasoning needs a little filling in. When I cover this argument in my ethics classes (and I do cover it in my ethics classes) I explain it in terms of opportunity costs. Money your family spends on food could have gone to charity. If you are able to cut back on your food budget by wasting less, you can give more money to UNICEF. Of course, for the argument to really work, you must actually give money to charity when it becomes available, rather than just wasting it some other way.
As it turns out, you can quantify this kind of waste on a global scale. This is one of the things Smil (2004) does. One of the reasons I like Smil is that he deals with large scale figures that span economics and environmental health. For instance, he keeps track of the ratio of GDP to energy consumption of many countries, to figure out if we are wasting the most basic resources available to us. The problem with Smil's big numbers is that they are often very rough estimates, and since few others do the kind of research he does, there aren't many models that can help us make sense of these numbers.
In any case, one of the most interesting numbers is the ratio of calories available to a country to the calories actually consumed, the difference representing waste in the food chain. Smil summarizes the standard this way:
With the actual daily food requirements of modern urban societies averaging no more than 2000-2200 kcal/capita it does not make any sense to supply more than about 2,700-2,800 kcal/day: Wasting 20-30 per cent of all available food is surely enough.As it turns out, though, only the Japanese actually use food this efficiently. The US actually supplies 3,700 kcal/day, which means like 43% of our food is wasted. China, too, is rolling in food, with 3,000 kcal produced for every person in the country every day.
But, you say, is table waste really a big factor here? Doesn’t most of the waste happen in production and shipping? Well, at least in China, Smil suggests, table waste is a problem: “Waste is encouraged by an unfortunately Chinese habit of ordering more food than can be eaten by hosts desiring to gain face, and by widespread, and often astonishingly ostentations, dining at public expense” (107). I had the chance to experience this when I was in China. Wherever we ate, we had to leave huge piles of uneaten food on the table. Anything else would be a slight to our host. Once, one of our number made the mistake of suggesting that a Chinese guest could take some of the extra food home. The unintended insult lead to shouting: “I am not a dog!” Furthermore, all business in China appears to be conducted over rounds of competitive drinking, which can get completely out of hand. One member of our group dishonored himself by declining a challenge to drink from one of our Chinese hosts, a loss of face furthered by the fact that the challenger was female. Another member of our group dishonored himself by accepting too many challenges to drink. Doing business in China is very difficult.
Well, if Chinese table waste can show up in Smil’s calculations, table waste elsewhere can as well. So eat your peas!
Smil, Vaclav. 2004. China's past, China's future: energy, food, environment. New York: Routledge.