Science in Society Archive

Caution Needed for the Precautionary Principle

Prof Peter Saunders exposes major misconceptions and misrepresentations perpetrated by opponents

No definitive statement exists but there is a reasonable consensus

There is no definitive statement of the precautionary principle, but there is a reasonable consensus about what it says, at least among those who support it. The 1998 Wingspread Declaration [1] is typical:

“When an activity raises threats of harm to human health or the environment, precautionary measures should be takeneven if some cause and effect relationships are not fully established scientifically. In this context the proponent of an activity, rather than the public, should bear the burden of proof. The process of applying the precautionary principle must be open, informed and democratic and must include potentially affected parties. It must also involve an examination of the full range of alternatives, including no action.”

The European Commission in 2000 expressed it less succinctly [2], but it contains the key phrase at the beginning:

“The Precautionary Principle applies where preliminary objective scientific evaluation indicates that there are reasonable grounds for concern …” (italics added)

The statements of the principle by those advocating it or proposing to use it, are essentially similar. The principle is to be applied when (a) there is scientific evidence for a threat to the environment or to health, but (b) the evidence, while sound, is not conclusive. What is crucial is that there must be a prima facie scientific case for a threat. If there is not, then the principle does not apply, though of course any innovator should try to identify possible hazards as a routine part of the process of development.

If there is, then we do not have to wait until we are certain about the hazard before we can take measures to mitigate or avoid it. The precautionary principle states that we are permitted to act on the basis of evidence that is not conclusive. It does not, however, say that we are obliged to. What, if anything, we actually do is a matter for judgment on the basis of the evidence that we have in front of us.

The burden of proof is set to protect health & environment

The precautionary principle is something like the burden of proof. In a civil court the playing field is level, but in a criminal court it is deliberately not. The defendant is not required to prove his innocence; it is for the prosecution to prove him guilty beyond reasonable doubt.

The lack of balance is deliberate. Courts are supposed to convict the guilty and acquit the innocent. In an imperfect world that isn’t always going to happen, and the legal system has to allow for when it doesn’t.

There are two different ways in which things can go wrong, just like Type I and Type II errors in statistics. The view that we as a society have come to is that while it is undesirable that a crime should go unpunished, it is far worse for an innocent person to be convicted. So we shift the balance to make it less likely that will happen, which naturally means that we have to accept a greater probability that a criminal will be set free.

In the same way, when we act on the basis of evidence that is not conclusive, we are saying that we have reason to be concerned that something is hazardous and we are sufficiently worried about the consequences that we are willing to go without it, or at least to delay its introduction until we have more evidence.

Neither the burden of proof nor the precautionary principle is an algorithm for decision making. A jury still has to decide whether the defendant is guilty beyond reasonable doubt – and even what they are prepared to accept as “reasonable doubt”. In the same way, even if we accept the precautionary principle, we still have to weigh up the evidence as best we can, and we still have to decide how much reassurance we are going to require before we allow something to proceed. As in ordinary risk assessment, an important factor in this is how much we believe we stand to gain if it does go ahead.

Common criticisms

There are a lot of criticisms of the precautionary principle around; let us deal with them at the outset.

  • Ill-defined – Critics sometimes complain that there are so many definitions of the precautionary principle that it cannot be taken seriously. In fact, those that are not covered by the description above come from opponents, each setting up his or her own straw man to knock down. Then, to add insult to injury, they say that anything with so many different definitions is obviously too vague to be useful.
  • Vacuous –   Some complain that the precautionary principle does not lead to definite decisions. But that isn’t what it’s meant to do. Like the burden of proof, it is something we take into account when we are making decisions.
  • Incoherent – Others, evidently believing that the precautionary principle does lead to definite decisions, complain that because there can be risks on both sides of an action, it can “ban what it simultaneously requires” [3]. As above, the answer is that the role of the precautionary principle is to influence decision makers, not do their job for them.
  • Too weak – The ‘burden of proof’ in a trial does matter: people are acquitted who would be found guilty if criminal trials were like civil proceedings. See below for examples of where the principle could have a real effect. And while some people say it is too weak, naturally there are others who claim it is …
  • Too strong – Even with the burden of proof on the prosecution, many people do get convicted. In the same way, even if we adopt the precautionary principle, progress will continue. Almost all innovations will proceed without being challenged, just as they do now.
  • Anti-scientific – On the contrary, the precautionary principle is all about science. For it to apply at all, there must be scientific grounds for concern, and it then requires that more science must be done to allay (or not) those concerns. Sweeping but unsupported assurances that everything will be all right will not do.
  • An excuse for protectionism – Anything that can lead to a restriction can be used as an excuse for protectionism. But at least here the innovator has an opportunity to counter the objection, by providing real evidence that the concerns are unwarranted, or at least outweighed by the advantages.
  • These matters should be dealt with in the courts – This is really just another version of the misunderstanding that the precautionary principle is an algorithm for taking decisions, which it is not.

Critics of the precautionary principle often make up alarming stories of how it could stop progress dead in its tracks. Here is a typical example. “Imagine it is 1850 and the following version of the precautionary principle is adopted: no innovation shall be approved for use until it is proven safe, with the burden of proving safety placed on the technologist. Under this system, what would have happened to electricity, the internal combustion engine, plastics, pharmaceuticals, the Internet, the cell phone and so forth?” [4]

Not only is this all a flight of fancy, it depends crucially on a “straw man” version of the precautionary principle. The critics cannot provide examples where the precautionary principle was applied and resulted in losses. In contrast, it is easy to find real cases where lives and money were lost because the precautionary principle was not applied.

Some cases


The precautionary principle would not have prevented Sir Walter Raleigh introducing tobacco into Europe because at that time there was no evidence that it was harmful. We are told that in the late 1940s, when Richard Doll and his colleagues were trying to find out why lung cancer had increased, they had no idea that the cause was tobacco. The most likely candidate seemed to be the great increase in motor traffic during the War.

The epidemiological studies provided strong evidence that smoking was an important cause of lung cancer [5]. The sceptics, above all the tobacco industry, refused to accept this conclusion, demanding instead proof in the form of a clearly demonstrated mechanism. As a result, while it has been widely known since about 1950 that smoking is dangerous, it was only much later that our governments took any action. Had the precautionary principle been applied, they would not have waited for the proof the industry was demanding. They would have started much earlier to increase the tax on tobacco, ban advertising especially when aimed at children, ban smoking in public buildings, and so on.

It is obviously impossible to calculate how many lives would have been saved if governments had not waited so long. For one thing, we cannot say at what point they would have judged the evidence strong enough to justify going ahead over the objections of the tobacco industry. But the WHO MPOWER report [6] estimates that in the twentieth century, tobacco killed 100 million people. If we suppose that only one per cent of those lives would have been saved if the precautionary principle had led countries to act sooner, that is still a million lives. That in itself is a sobering thought, but we can, if we prefer, convert it into monetary terms by using the usual risk assessment valuation of a life as six million US dollars. That gives a total cost of six trillion dollars, massive even when compared with the amounts involved in bailing out the banks.


Most people probably believe that the danger of asbestos was discovered only 30 or 40 years ago and that action was taken as soon as it was. In fact, it was in London in 1898 that Lucy Deane, one of the first “Women Inspectors of Factories” noticed that people who worked with asbestos suffered more serious ailments than those who worked in other dusty environments. She even found a reason why: asbestos particles are sharp [7].

For the next hundred years, governments and the asbestos industry kept insisting that there was no conclusive proof that asbestos was as dangerous as we now know it is. They also maintained that there was no alternative for it, which we also now know there is. They therefore only gradually restricted its use. It was being installed in buildings in the UK as late as the 1970s, and it wasn’t until 1998 – the 100th anniversary of Lucy Deane’s report – that it was finally banned altogether in the UK and France.

For asbestos as for tobacco, we cannot really estimate how much was lost by ignoring the precautionary principle. We can,  however, get an idea of the scale by noting that in 2000 it was estimated that there were about a quarter of a million deaths from mesothelioma yet to come in Europe alone. That converts to about one and a half trillion dollars, not including all the deaths in the twentieth century, or the rest of the world, or asbestosis, or other costs.

This is something to bear in mind the next time someone complains about the unreasonable cost of adopting the precautionary principle.


When the evidence of harm is conclusive, it is clear that action is called for. The precautionary principle applies when there is scientific evidence but it is not conclusive. It is therefore alarming to read the justification offered by Wallace Hayes, the editor of Food and Chemical Toxicology (FCT) [8] for his unilateral decision to retract the paper by Séralini and co-workers [9] on the harm caused by Roundup herbicide and Roundup Ready maize. He admits that it was not a question of fraud, serious error, plagiarism or an unethical experiment, the only grounds for retraction specified by the Committee on Publication Ethics, of which FCT is a member. Instead, he retracted the paper because in his opinion the results are “inconclusive.” In other words, the precautionary principle should be replaced by the principle that if evidence is inconclusive it should be suppressed.

In fact, the paper of Séralini and his co-workers is only one of a large number of papers in which GM crops and the herbicide to which they are made tolerant have been shown to be harmful both to health and the environment. There is no need to apply the precautionary principle; taken as whole, the evidence is far from inconclusive. (See [10] Ban GMOs Now - Special I-SIS Report, [11] The Bradford Hill Criteria Applied to Climate Change & GMOs, SiS 45). That is why there is now an active campaign condemning the retraction and pledging to boycott the journal publisher unless and until the retraction is reversed [12] Open Letter on Retraction and Pledge to Boycott Elsevier, SiS 61).

To Conclude

By itself, the precautionary principle does not stop anything. On the contrary, it could well lead to creative alternatives and solutions. What it does is prevent governments and regulators from deliberately ignoring a strong scientific case by using the excuse that there is no proof of danger. It prevents companies from insisting that they must be allowed to carry on until absolutely conclusive scientific proof is available.

Where it is accepted, the precautionary principle makes it much more difficult for companies to demand damages from regulators, as the Ethyl Corporation was able to do when the Canadian government passed legislation banning the fuel additive MMT [13]. Because the Precautionary Principle shifts the burden of proof on to the perpetrator, and given the doubts about MMT (there was already a partial ban in the US) Ethyl would have been required to show that it was safe.  

Ethyl brought its case not under Canadian law but under the North American Free Trade Agreement (NAFTA). There is a real danger that the proposed Transatlantic Trade and Investment Partnership [14] will similarly undermine the precautionary principle within the EU. Laws and regulations within a country (including an entity such as the EU) have to be debated in public and are expected to reflect the values of that country; international agreements are largely free of such constraints and generally assign a high status to trade as a value in itself.

If the precautionary principle were implemented, most innovations would proceed without interference just as they do now.  Some, however, would not. There would be a cost attached to that, as there is in all regulation, but history has shown us that the cost of ignoring warnings can be very great indeed.

An earlier version of this article appeared in Policy Responses to Societal Concerns in Food and Agriculture, published in 2010 by the OECD [15].

Article first published 16/12/13

Notes and References

  1. Science and Environmental Health Network. The Wingspread Consensus Statement on the Precautionary Principle, 1998, accessed 4 December 2009,   .
  2. European Commission. Communication from the Commission on the Precautionary Principle, 2000, accessed 13 December 2013,
  3. Sunstein CR. Throwing precaution to the wind. Boston Globe, 13 July, 2008, accessed 12 December 2009,  
  4. Graham JD. The Perils of the Precautionary Principle: Lessons from the American and European Experience. Speech at the Heritage Foundation Regulatory Forum, 2003, accessed 4 December, 2009,  
  5. Doll R and Bradford Hill A. Smoking and carcinoma of the lung. British med. J. 2, 1950, 739-748.
  6. World Health Organisation. WHO Report on the Global Tobacco Epidemic, 2008 The MPOWER package. WHO, Geneva, 2008. ISBN: 978 92 4 159628 2.
  7. Harramoës P, Gee D,  MacGarvin M, Stirling A, Keys J, Wynne B and Guedes Vaz S  (2002). Late lessons from early warnings: the precautionary principle 1896-2000 European Environment Agency, Copenhagen. ISBN 92-9167-323-4.
  8. Elsevier announces article retraction from journal Food and Chemical Toxicology. Press release, 28 November 2013, accessed 9 December 2013, 
  9. Séralini G-E, Mesnage R, Gress S, Defarge N, Malatesta M, Hennequin D and  de Vendômois JS.  Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize. Food and Chemical Toxicology, 50, 2012, 4221-4231.
  10. Ho MW and Sirinathsinghji E. Ban GMOs Now, ISIS, 2013,
  11. Saunders PT. The Bradford Hill Criteria applied to climate change & GMOs. Science in Society 45, 24-25, 2010.
  12. Becker HA, Clark EA, Cummins J, Davidson RM, de Guzman LE, DelGiudice E, Dotson RS, Exley C, Haffegee J, Ho MW, Huber DM, John B, Mason R, Mendoza T, Novotny E, Oller JW, Palmer J, Pollack G, Pusztai A, Samsell A, Saunders PT, Shiva V, Sirinathsinghji, E, Swanson N, Seneff S, Tomlijenovic L, Zamora O. Open letter on retraction and pledge to boycott Elsevier. Science in Society 61.
  13. See for example the bill introduced into the California State Legislature by Senator Soto.
  14. European Commission. The Transatlantic Trade and Investment Partnership. 27 November 2013,  accessed 9 December 2013,
  15. Saunders PT. The precautionary principle. In Policy Responses to Societal Concerns in Food and Agriculture, Proceedings of an OECD Workshop. OECD, Paris, 2010, pp.47-58.

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There are 2 comments on this article so far. Add your comment above.

Todd Millions Comment left 22nd December 2013 09:09:50
Love your Italics-You use some of my favorite examples-MMT-was prequiled by leaded(doped) gasoline,not a superiour product but a cheaper,more toxic subsitite,PR engineered to hide that cracked(catalyst) gasoline,was a poor subsitute for distilled grade,requiring increasingly rare light oil-in the 1920's mind.Yes- they were warned by US army poison warfare experts NOT to use it,and an entire 3 generations of engineering profs and students had to be conditioned to chant the holy standard oil line about how internal combustion engines worked-too pull it off,despite german engines with methanol injection out performing leaded aviation gas in WW2.Beleif vs evidence.Is there any evidence that the pr 'proof'(assertation)- that bt cotton,worn against the skin won't have the toxins leach thru to the blood stream?I find no tests-even biowennie ones for this claim.Tobbaco-more on that shortly.

Allison Lee Sears Comment left 10th January 2014 19:07:16
This has to do with the"precautionary clause" or the burden of proof: if you would look at this site: You will see how the EU is set up: the responsibilities of the Commission, the Parliament and the Judicial System. It seems the the European Commission has it's on prescribed venue, and will not lapse from it. The Commission sets up all laws,, regulations formalities. The Parliament can't add to the ruling, nor subtract from it. The Judicial is simply a tribunal that only carries out exactly what the Commission wants. Unfortunately, they are actually for GMO food, vaccinations and pharmaceutical drugs that are in question. GMO food is just about the worst of the worst. Recently a study done with English and American scientists (impartial to Monsanto) found a tremendous amount of tumors and cists in mice, proving the harm caused by Monsanto. You must keep going and don't give up. Thank you for your perseverance. Interesting Points:: in America, many zoos won't give GMO food to the animals: they are to expensive. The White House won't serve it, Martha Stewart won't eat it. Opra Winfrey won't eat it, and last year when the Bilderbergs had a Conference in Chantilly, Virginia, they closed down the Mariott Hotel, and brought in their own food: NON-GMO food. Oh yes, did you know that the Monsanto scientists won't eat GMO food? America should never ever ship GMO food products to Europe, Asia, Africa - or anywhere. Our bodies must have nourishment. We need all trace minerals, organic plants, natural fruit and what ever the earth provides, naturally. Our liver sees anything that is man-made as toxic and goes into full force to attack it and get it out of our bodies - this puts constant stress on our liver. You know all about the liver and know how full well it is important to our very health. Monsanto's plants, are chemically made by manipulating genetics. The Guanine, Adenine, Thymine and Cytosine are all basically plastic and without true life. Because of this, we are loosing bees, worms,ladybirds, praying mathis and especially frogs. Frogs and bees and worms are the key to seeing the health of a piece of land. Nothing else matters because our health depends on nourishing food from a land that is nourished. Forgive me for carrying on, but my "step-father" was an Englishman: Robert Payne, a writer of history and biographies and he taught me: stay curious, look at all sides of an issue whether you like the outcome or not, stay focused on anything that could cause harm. Also an artist and love to problem solve. Thank you and do carry on, this world needs you and your voice.