The Irrational Precautionary Principle

Should New Substances Be Banned Until Proven Harmless?


Chlorine is a common chemical. It’s estimated to be used in the production of 80 percent of all pharmaceuticals. But like most chemicals it can cause problems depending on the dose, what it is mixed with, and how it is used. On one hand, it is used to disinfect drinking water and saves millions of lives every year. On the other hand, it is a component in compounds that are believed possibly to cause cancer or other health problems. When the U.S. Environmental Protection Agency said that a chlorine byproduct presented a cancer risk, officials in Peru stopped using chlorine to disinfect drinking water. The resulting cholera outbreak killed thousands of people.1

The Green Left is today pushing a new legal principle that would seem to mandate that governments around the world repeat this disaster. It’s called the Precautionary Principle. It means that any new technology or substance should be banned or restricted until it is proven harmless. Of course, life is rarely that simple. Even if chlorine slightly increases the risk of cancer, it dramatically reduces the risk of dying. But the environmentalist doesn’t seem to understand this. Joe Thornton, who was an analyst for Greenpeace, has written: “We need to treat organochlorines as a class. There are 11,000 in commerce plus thousands more that are produced as by-products. It would be truly impractical to regulate them one-by-one. . . . It makes sense to treat organochlorines as guilty until proven innocent.”2

Any such rule that treats all chlorine as the same would be impractical. A ban might save a few lives from some forms of cancer, but it would surely cost millions of other lives because of impure drinking water.

The precautionary principle says we shouldn’t allow something to happen as long as someone believes it may be a threat and until we can prove that it isn’t harmful. A coalition of Green groups enshrined this concept in the Wingspread Statement, which said: “In this context the proponent of an activity, rather than the public, should bear the burden of proof.”3

Of course, the “public” referred to is not the public at all but the Green groups themselves.

As Jeremy Leggett wrote in Global Warming: A Greenpeace View: “The modus operandi we would like to see is: ‘Do not emit a substance unless you have proof it will do no harm to the environment.’”4 The European Commission took the principle to heart. When it banned animal-growth hormones in 1985 it did so not because of any evidence on hand, but because their safety had not been conclusively proven.

Imagine what the precautionary principle would require in day-to-day living. We are faced with choices and tradeoffs every day. Doing one thing precludes doing other things. We can’t go to the movies on Friday night and at the same time visit the in-laws. But the precautionary principle would strip us of entire classes of options. Normally, if you have to decide whether to do something or not, you weigh evidence and choose accordingly. If you applied the precautionary principle instead, you’d do nothing. You would only go to the movies if you could prove in advance that going was better than not going. But how could you do that?

We’ve all gone to films that were wonderful experiences, and no doubt we’ve also been to some so abysmal that we walked out before the end. We are certain that the choice was good only after the fact. We can make educated guesses, but we can’t prove, in advance, that one option is better than another.

The precautionary principle is tantamount to a coup in legal theory. Say a developer wants to build an apartment and a Green group condemns the plan, saying it’s “harmful to the environment.” The group would not have to present any evidence to stop the developer. Rather, the developer would have to prove that all possible outcomes from his plan are good. But he could never do that. This would also be true for the inventor, scientist, industrialist, and virtually anyone else who has to deal with the physical world—in other words, all of us. We must remain stagnant until we can prove that any particular action is good under all possible scenarios.

The established principle that puts the burden of proof on those who would block free action is clearly superior to the precautionary principle. The reasons are relatively simple. We can’t know the future, and we can’t prove a negative. We don’t incarcerate people because they belong to a group or class that might commit a crime. But the precautionary principle says that anything that deals with the environment—and that really means everything—is deemed dangerous until proven otherwise.

That principle drives the environmentalist agenda. There is no convincing evidence that biotechnology is dangerous to humans, but the environmentalist lobby posits theories, unsupported by facts, that such a danger might exist. Therefore it demands that biotechnology be proven safe. How? No answer—because there is no answer. One can disprove a positive but not prove a negative.

Treaties Embody Principle

This theory is now embedded in various UN treaties and the proclamations of international bodies:

  • The UN’s Convention on Biological Diversity states, “[L]ack of scientific certainty should not be used as a reason for postponing measures to avoid or minimise such a threat.”
  • The UN’s Framework Convention on Climate Change states, “lack of full scientific certainty should not be used as a reason for postponing such measures” that prevent actions from being taken.
  • The UN’s 1992 Rio Declaration states: “In order to protect the environment, the precautionary principle shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.”
  • Author Jonathan Adler notes that the UN’s Cartagena Protocol on Biosafety “creates mechanisms whereby national governments will be able to restrict, or even prohibit, the importation of genetically engineered crops.” Like many environmental treaties, the preamble of the protocol “reaffirm[s] the precautionary approach” contained in the Rio Declaration. The protocol goes further, however, by explicitly stating that “lack of scientific certainty” about potential risks of biotech products “shall not prevent [a member] from limiting or banning such products.”In other words the lack of evidence does not mean something cannot be declared guilty.5

The principle first appeared in the 1982 UN World Charter for Nature. The charter said that “Activities likely to pose significant risks to nature shall be preceded by an exhaustive examination; their proponents shall demonstrate that expected benefits outweigh potential damage to nature, and where potential adverse effects are not fully understood, the activities should not proceed.”6

Inertia thus becomes the primary human state, and everything must be justified in advance because it is deemed harmful until proven beneficial. In addition, proponents must show that no possible alternative is safer.

Understandable Attraction

One can see the attraction of the precautionary principle to the environmentalist lobby. From the start the lobby was long on scare-mongering and short on facts. Even when sufficient time has gone by to test its theories, many claims have failed to be substantiated. No wonder, then, that Joel Tickner, in the newsletter for the Science and Environmental Health Unit, argues for the principle in this manner: “Proving cause takes extensive time and resources.”7 It’s much easier to merely assert harm and let your opponents grapple with the impossibility of proving it isn’t so.

The environmentalist Institute for Science in Society has admitted that “The precautionary principle is about the burden of proof.”8 Peter T. Saunders of King’s College in London even compares the precautionary principle to the burden principle used in the courts: “Just as society does not require a defendant to prove his innocence, so it should not require objectors to prove that a technology is harmful.”9But this is backwards. In a rational process, the new technology is the defendant—innocent until proved guilty—and the objector is the prosecutor with the burden of proof.

At least one prominent advocate of the precautionary principle is candid about his reasons for turning that legal maxim inside out. Boston University law professor George Annas says: “The truth of the matter is that whoever has the burden of proof loses.”10

Be that as it may, the precautionary principle is appealing to the environmentalists because, in the words of Britain’s Social Issues Research Centre, “it prevents scientific debate.” The Centre adds: “The burden of evidence and proof is taken away from those who make unjustified and often whimsical claims and placed on the scientific community which, because it proceeds logically and rationally, is often powerless to respond. This is what makes the principle so dangerous. It generates a quasi-religious bigotry which history should have taught us to fear. Its inherent irrationality renders it unsustainable.”11


  1. Michael De Alessi, “Precautionary Principle Is Risky Gambit,” San Francisco Chronicle, July 16, 2003.
  2. Quoted in Jonathan Adler, “The Precautionary Principle’s Challenge to Progress,” Global Warming and Other Eco-Myths (Roseville, Cal., Prima Publishing, 2002), p. 274.
  3. Available at
  4. Jeremy Leggett, Global Warming: A Greenpeace Report (Oxford: Oxford University Press, 1990), p. 459.
  5. Adler, p. 282.
  6. See
  7. Joel Tickner, “Precautionary Principle,” The Networker, May 1997,
  8. Peter T. Saunders, “Use and Abuse of the Precautionary Principle,” Institute of Science in Society, July 13, 2000,
  9. Quoted in Ronald Bailey, “Precautionary Tale,” Reason, April 1999;
  10. “Beware the Precautionary Principle,” Social Issues Research Centre, no date,