新编大学英语第二册unit10 Text C: Risks from Nature and Technology
UNIT 10 AFTER-CLASS READING 2; New College English (II)
Risks from Nature and Technology
1 We live in an age when natural has come to mean "benign" and anything made by humans seems both artificial and suspect. But actually the natural and the benign are not necessarily the same thing. Nature does a lot of nasty things to us. Floods, storms, earthquakes, hurricanes, volcanoes, and tornadoes are just the tip of the iceberg. Most diseases are natural. Many naturally occurring substances are poisonous. The single largest source of cancer-producing radiation is radon gas, a byproduct of the decay of radioactive elements in the earth's crust. Other sources of cancer-causing radiation are cosmic rays and ordinary sunlight. Indeed, death itself is natural. If we have been able to prolong life beyond its traditional span of seventy years, that is because we have been clever enough to contrive ways of delaying the decay, disease, and destruction that is inflicted on us by nature.
2 Think about it another way. All plants, including those we eat, contain many naturally occurring pesticides. They have evolved these toxic in many cases, carcinogenic defenses against insects and other predators over millions of years. It has been estimated that we consume 10,000 times as many natural pesticides as artificial ones. In other words, nature is not benign. Other numbers prove this even more convincingly. It is a widely used rule of thumb among risk specialists that, in any given year, about 30 times as many people will die in natural disasters as in manmade ones.
3 In addition to natural catastrophes, there are still plenty of ways in which our technological society poses major threats to our lives and health, especially through damage to the environment in which we live. The unhappy fact is that we have some grounds for thinking that many air and water pollutants may be risky, but we have as yet no dependable data on the size of the risk they pose. In other words, although we have a pretty good idea of the amount of the principal pollutants released into the air and water in the United States, there are very few studies on the health effects of specific concentrations of particular pollutants. Such studies are difficult to perform because there are too many variables outside our control. Is a certain oxide of nitrogen dangerous in a particular amount? Usually the answer is that we do not know.
4 Because everything is risky, it is meaningless to be told that this or that pollutant poses a "potential" risk until we know what the risk level is. Unless we know whether a certain pollutant in certain concentrations kills 5,000 people a year or 1 person every decade, we cannot decide whether it poses an unacceptable risk. Scientists have generally not yet been able to identify the size of many of the risks posed by most of the pollutants in the environment.
5 In fact, such studies as there are raise doubts about the commonly assumed risks of some pollutants. In New York City, for instance, levels of sulfur dioxide fell more than 90 percent between 1969 and 1976 in response to the Clean Air Act of 1970. Despite this major shift in one of the most common air pollutants, daily mortality rates in New York did not change at all. No doubt New York City smells better, but it is unclear whether any lives were saved by the reduction in sulfur emissions.
6 The problem of assessing environmental risks is made worse by the official doublespeak on the subject. Consider but one example. From time to time, a federal agency will announce that it has identified a certain substance (natural or artificial) as a "possible human carcinogen". Such announcements are generally greeted with much wringing of hands from the general public, who suppose that one more item must be taken off their menus. The facts, however, are quite otherwise. To qualify as a possible human carcinogen, there must be evidence that the substance in question produces cancer in rats when they receive doses of the substance that are often a million times stronger than a human being receives, even allowing for differences in body weight. Even if we suppose that the likelihood of cancer varies directly with the level of exposure and that whatever is carcinogenic to rats is dangerous to humans (and both assumptions are dubious), these figures mean that the likelihood of a human being getting cancer from normal exposures to the substance is about a million times smaller than the rat's chances. If you reflect on the other risk statistics, it will become clear that such a risk is extraordinarily low in fact, it is about as close to "safe" as we normally get in this life. Accordingly, the discovery that something is a possible human carcinogen is the discovery that it may be less harmful than many of the things we routinely do.
