Not so silent spring

A bit late for the 50th anniversary, but prompted by a remark made by a friend who shall be nameless.

Rachel Carson’s book Silent Spring, first published in 1962, is widely regarded as responsible for the initial impetus given to the “green” movement – the book that blew the whistle on humankind’s detrimental impact on the environment. It certainly had a big influence, both on the general public and on policymakers and the chemical industry; but as with so many influential books the interpretation put on the author’s work is not always what the author seems to have intended.
The fact that Carson knew she was seriously ill with cancer at the time she was writing Silent Spring may explain some of the over-the-top passages in the book, which did a lot of good in making people aware of the need for caution when interfering with the “balance of nature,” but doesn’t pass muster as a cool scientific appraisal of the problem. What Carson specialised in was passionate, poetic writing that got at her readers emotionally, as in the passage which gave her the title of the book:
It was a spring without voices. On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices there was now no sound; only silence lay over the fields and woods and marsh.
This is, of course, fiction – Carson’s vision of the potential future if chemical pesticides continue to be used indiscriminately, not a report of anything Carson had actually seen. But it was based on a nugget of fact. Soon after she had moved to Maryland, in January 1958 Carson heard from a friend, Olga Huckins, who owned a bird sanctuary. The sanctuary, like all its surroundings, had been liberally sprayed from the air with insecticide, as part of a government programme to eradicate pests. Many of the birds were directly affected, while many beneficial insects died along with the pests; her friend asked Carson, by then a famous biologist, if she could exert any influence on the government to investigate pesticide use and control it more effectively. Carson had for some time been worried about the widespread use of pesticides; following this letter, the more she looked into the matter, the more concerned she became, and the upshot was that she spent almost four years researching and writing what became Silent Spring.
The background to the book was the widespread use of insecticides, in particular DDT, in the post World War Two era. The power of DDT (dichloro-diphenyl-trichloroethane) as an insecticide had been discovered in Switzerland in the late 1930s, by Paul Müller, a chemist working for the Geigy company. It was developed on an industrial scale in the United States during the war, and used on a massive scale to combat typhus (spread by lice) and malaria (spread by mosquitoes) which were causing crippling losses to American troops – according to General Douglas MacArthur, before the introduction of DDT at any one time two-thirds of the troops in the South Pacific were afflicted with malaria. Under wartime conditions, vast areas were covered with DDT using bombers carrying containers of the insecticide under their wings; in a famous example of the power of DDT, in 1944 a potentially catastrophic typhus epidemic in Naples was stopped in its tracks by dowsing a million people with DDT powder.
There is no doubt that DDT and other insecticides did a lot of good – and still do a lot of good. In Italy, there were 411,062 cases of malaria in 1945, and only 37 in 1968. In the southern United States, malaria has been essentially wiped out, and many people who live there don’t even know that the disease used to be endemic. Tens of millions of lives have been saved by DDT alone in countries such as India and the Philippines. The trouble was that the wartime approach, the “can do” mentality that saw mankind as supreme over nature, carried over, particularly in the Untied States, into peacetime. To take just one example, when Dutch Elm disease (a problem caused by beetles in the bark of the trees) affected the campus of Michigan State University in the mid-1950s, the whole area was liberally sprayed with the poison. In an unanticipated consequence, leaves coated with poison fell to the ground and were eaten by earthworms who were in turn eaten by robins, who died. Or as Carson put it, in her lyrical way, “we spray our elms and following springs are silent of robin song, not because we sprayed the robins directly but because the poison traveled, step by step, through the now familiar elm leaf-earthworm-robin cycle. These are matters of record, observable, part of the visible world around us. They reflect the web of life – or death – that scientists know as ecology.”
There is another aspect to the problem, also discussed by Carson. Pests become resistant to pesticides. When a new pesticide is first introduced, it kills a lot of pests, but the individuals who survive are the ones with the strongest natural resistance to the pesticide. When they breed, their offspring inherit this resistance. Over many generations – and insects breed quickly – this builds up a large population of resistant individuals. Like the development of strains of disease organisms (“Superbugs”) resistant to drugs, it’s an example of evolution at work, or in Carson’s words, “a triumphant vindication of Darwin’s principle of the survival of the fittest.” The more miraculous a wonder drug or pesticide seems to be, the more important it is to use it thoughtfully, holding it in reserve for cases of real need, so that it will retain its effectiveness as long as possible
In her discussion of this, and her examples of the direct threat to the web of life, Carson was on solid ground. She did not say that all chemical insecticides should be banned, but that they should be used with discrimination to target specific pests. She also urged the use of biological controls, introducing natural predators to eat the pests – although it has to be said that this approach also requires extreme caution lest the cure turns out to be worse than the disease. But she did also exaggerate the problems, especially in her chapter concentrating on the alleged cancer-causing potential of chemical pesticides.
In publicity terms, this was a masterstroke. In the early 1960s, even more than today, cancer was the big health fear, the unspeakable disease. It’s one thing to be concerned that pesticides may be killing robins; quite another to be worried that they might be killing you. Among the “evidence” Carson included in her book was the example of a woman who sprayed her basement with DDT to eradicate an infestation of spiders and became ill. “When examined by Dr [Malcolm] Hargraves she was found to be suffering from acute leukaemia. She died within the following month.” And there is also the example of another patient of Dr Hargrave, a man who sprayed the basement of his office building to get rid of cockroaches. “Within a short time he began to bruise and bleed. He entered the clinic bleeding from a number of haemorrhages. Studies of his blood revealed a severe depression of the bone marrow called aplastic anaemia . . . nine years later a fatal leukaemia developed.” Such anecdotal examples are so ludicrous as to be laughable as “evidence” that DDT causes leukaemia. But they are still in the current edition of the book, and still causing concern. For that reason, it is worth stressing that five decades after Silent Spring was published, in spite of many properly conducted studies, no evidence at all has been found that DDT causes cancer in people. The cancer chapter is the worst blot on what is, overall, still an important book, if Carson’s message is correctly interpreted.
The book first appeared as a serialisation in the New Yorker in June 1962, and between hard covers later that year. It provoked a furious response from many sections of the chemical industry, but the resulting publicity only served to boost sales; the Book of the Month Club alone printed 150,000 copies just for its initial mailing to members. Above all, whatever its faults, Silent Spring boosted public and government awareness of the human impact on the environment. The immediate response of President John F. Kennedy was to request a report from his Science Advisory Committee, which in 1963 echoed Carson’s main (and now totally uncontroversial) message, pointing out that pesticides were needed to maintain the quality of American’s food and health, but warning against their indiscriminate use, saying that uncontrolled use of such poisonous chemicals was potentially “a much greater hazard” than radioactive fallout.
Groups such as the Natural Resources Defense Council, the Wilderness Society, and the Environmental Defense Fund were established during the years following publication of the book; the establishment of the Environmental Protection Agency in 1970 owed much to Carson’s legacy; and DDT was banned entirely in the United States in 1972. As Al Gore wrote in an introduction to the 1994 edition of Silent Spring, the book “brought environmental issues to the attention not just of industry and government; it brought them to the public.” Without this book, he said, “the environmental movement might have been long delayed or never have developed at all.”
But why did responsible bodies such as the President’s Science Advisory Committee take the pesticide threat so seriously? It wasn’t just because Rachel Carson wrote so powerfully and tugged at their heart strings. It was because exactly at the time her book was alerting the public to the dangers in emotional terms, hard scientific evidence was coming in that pesticides such as DDT and dieldrin were far more ubiquitous in the environment than anyone had realised.
Just at the time Carson was writing her book, the electron capture detector was being used independently by scientists at the Shell Research Centre in Kent and those of the US Food and Drug Administration to measure the residue of pesticides in the environment. It quickly became clear that pesticides such as DDT and dieldrin were present everywhere, including in the tissues of people and other animals. In Lovelock’s words, “this lent veracity to Carson’s otherwise unprovable statements.” Although she rightly gets credit for sounding the warning in clear language and getting the public emotionally involved, “people often forget the positive role played by scientists in both industry and government agencies in establishing the reality and magnitude of the problem.” It was evidence obtained using electron capture detectors, not the emotional arguments alone, that finally led to the DDT ban in the United States.
At first, Lovelock was delighted by this use of the ECD, since even in those pre-Gaia days he shared Carson’s views on ecology and the web of life, and was already concerned about damage to natural ecosystems. When she wrote “the earth’s vegetation is part of a web of life in which there are intimate and essential relations between plants and the earth, between plants and other plants, between plants and animals,” she struck a chord. In a CBS documentary in which she appeared in 1964, not long before her death, Carson said:
Man’s attitude toward nature is today critically important simply because we have now acquired a fateful power to alter and destroy nature. But man is a part of nature, and his war against nature is inevitably a war against himself.
This is a message that resonated with Lovelock at the time, and resonates with us today. But, says Lovelock, “you have to have a bit of common sense” when using an instrument as sensitive as the ECD. It is so sensitive that “it can detect absolutely trivial quantities of pesticides and other pollutants. Even organically grown vegetables contain measurable amounts of pesticides, if you use an ECD to make the measurements.” This means that it doesn’t make sense to set the lowest permissible level of pesticides in food, for example, as zero, because “you’d have to reject nearly everything we eat.” Lovelock likes to quote the sixteenth century German physician Paracelsus, who said “the poison is the dose,” and points out that pure water will kill you if you drink too much of it, while the deadliest nerve gases are not deadly at all in quantities measured in a few picograms, which the ECD can easily detect. By nature a quiet man, for all his determination, one of the few things that rouses him to anger is the way “self-styled Greens” who “not only know nothing of science, but actively disdain science,” are “happy to use the results from ECDs and other scientific instruments to support misguided crusades to get everything banned. Even if we restrict ourselves to DDT, they forget that even today it saves millions of lives in the Third World. If that means a measurable but insignificant trace of DDT getting in to the food chain, it doesn’t matter, and I’m sure Rachel Carson would agree.”

Adapted from our biography of James Lovelock.


How do you insure against meteorite impact?

Following recent events in/over Russia, I thought this might be of interest.

It is estimated that 2000 asteroids each more than a kilometre across are in Earth-crossing orbits, accompanied by a million objects between 0.1 km and 1 km across and at least 500 million smaller objects (down to 10 metres across).
So the threat is certainly real.  But how do you measure such threats?  How do you decide what response is cost effective?  The best analysis, so far, of the risks involved has been carried out by Clark Chapman, of the Planetary Science Institute in Tucson, Arizona, and David Morrison, of the NASA Ames Research Center at Moffett Field, in California.  It was published in Nature on 6 January 1994 (volume 367, page 33), and has since provided the basis for all attempts at deciding how best to combat the threat from space.
Chapman and Morrison drew on several studies carried out during the 1980s and early 1990s, most of which had been inspired, directly or indirectly, by the realization that the Earth had suffered a major cosmic impact at the end of the Cretaceous.  The bottom line of their calculation is that there is a 1 in 10000 chance that an object bigger than 2 km across will strike the Earth in the next century, causing major disruption of the world’s ecosystem and killing a large proportion of the human population of the planet.  The risk is very small, but the number of people potentially affected is very large, and in statistical terms that puts the risk to any individual human being surprisingly high up the scale of things to worry about, using the actuarial approach of life insurance companies.
For any present-day citizen of the USA, the chance of being killed by the after effects of a cosmic impact are about 1 in 20000.  This is bigger than the risk of being killed in any other kind of natural disaster, and is exactly equal to the risk of being killed in an airplane accident on a commercial passenger flight, something that very many people take seriously as a risk to worry about.  It compares favourably with the chance of being killed in a motor vehicle accident of 1 in 100, and with the danger of accidental electrocution of 1 in 5000, but unfavourably with the chance of being killed by a tornado (1 in 60000), and with the risk of death by food poisoning (just 1 in 3 million).  THe risk of death from cosmic impact is greater than the combined risk of death from tornadoes, hurricanes, earthquakes, forest fires and volcanic eruptions.
The point is, as Chapman and Morrison put it, that “impacts are an extreme case of a low-probability/high-consequence hazard”.  In his book Exploring Planetary Worlds, Morrison spells out how the odds are calculated.  If an impact big enough to cause a global crop failure happens once every 375,000 years, and you have a 1 in 4 chance of dying if such an impact occurs in your lifetime, then the annual risk of death from this cause is 1 in (3 x 375,000), which is 1 in 1.5 million.  If the average human lifetime is 75 years, the overall chance of being killed in this way is 75 times greater — 75 in 1.5 million, or 1 in 20000.
The chance of anyone at all being affected in this way is indeed small; but if one person is affected by a major cosmic impact then literally billions of other people will suffer as well.  This changes the way you should think about the risk.  For example, many cautious people buy cheap “one off” life insurance policies every time they fly, so that if that 1 in 20000 risk comes up, their dependents will, at least, have financial security. But there is no point in taking out comparable life insurance against the risk of death in a major cosmic impact, because if that event happens you probably won’t leave any surviving dependents, and in any case there will be no insurance company left to pay up.  The only kind of “life insurance” against a major cosmic impact is to take global precautions, and the cost of those precautions should be seen in exactly those terms — as life insurance for billions of people.  Divide the cost of the precautions by the number of people in the world (or even in the USA and Europe) and you have a sensible figure for the cost of the insurance in personal terms.  This makes current proposals put forward by astronomers to keep a proper watch out in our neighbourhood of space look very cost effective — certainly better value for money than those one-off airline flight insurance premiums.
The chance of any one person being killed by a major comet impact in any one year is only about 1 in 2 million, but that still means that on average 2,700 people are killed by large comets each year, 390 of them in the developed world alone.  Putting this in a slightly different perspective, the cost of road safety measures in Britain in the mid-1990s works out at just over £800,000 for each life that is saved.  If we cared as much about the comet and asteroid hazard as we did about road safety, that would imply that the developed world ought to be spending nearly $500 million a year to prevent cosmic impacts.  The fact that nobody is killed by such  an impact for many years, and then many people are killed at once, does not alter the argument.  There are long stretches of road where nobody is killed for many years, and no big accidents occur; but that is not a good argument for saving costs by not bothering to maintain safety barriers and decent lighting on those stretches of road on a year by year basis.

Adapted from Fire on Earth, by John Gribbin & Mary Gribbin.  Now sadly out of print.