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Welcome to PSR's Environmental Health Policy Institute, where we ask questions -- then we ask the experts to answer them. Join us as physicians, health professionals, and environmental health experts share their ideas, inspiration, and analysis about toxic chemicals and environmental health policy.


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The Abuse of Scientific Uncertainty

Posted on October 7, 2010

By Michael McCally, MD PhD

This essay is in response to: How can we set science-based policies in the face of scientific uncertainty?

The present moment is a gloomy one for attention to urgency of climate change. In July of 2009, cap and trade legislation failed definitively in the US Congress. The Kyoto Protocol of the United Nations Framework Convention on Climate Change, the initiative of 187 nations to control greenhouse gas emissions, died in Copenhagen in December of 2009. The opponents of action on climate change have successfully abused the notion of scientific uncertainty to create doubt and justify inaction.

How can we proceed? I believe that there are lessons from work in other contested policy fields such as the regulation of tobacco that might help us in the pursuit of urgently needed policies in climate change and toxic chemicals. 

Experimental science is a process of approximation.  Few studies are definitive and most are not. Progress in scientific understanding relies heavily on the weight of evidence. Over time evidence accumulates from different types of studies by scientists of differing disciplines creating, finally, a scientific consensus.

In the late 1950s Roger Revelle of Scripps Institution of Oceanography wrote of the potential impacts of carbon dioxide-caused global warming and hired Charles Keeling to begin measurements of atmospheric carbon dioxide. Over fifty years data has accumulated from thousands of studies of temperature, weather events, arctic ice, glaciers, and ocean chemistry. The task of the IPCC has been to evaluate and assemble this huge body of science.

In each subsequent IPCC Assessment - there have been four over twenty years - the evidence of human influence on climate has been more firmly established. Today all but a tiny handful of scientists believe that the globe is heating and that anthropogenic greenhouse gas emissions are the major cause. Similarly in 1950s the health effects of smoking began to be studied. Today it is universally accepted that cigarette smoking causes cancer and that nicotine is addictive.

But why did it take so many decades to develop scientific and public consensus? One answer is that this is the way science works. It takes time to develop the weight of evidence sufficient to convince. Experts may differ in their judgment of the weight. The second more important answer is that in contested fields, opponents of policy may deliberately create doubt about science to obfusticate the facts and delay decision-making. The deliberate creation and marketing of doubt, the abuse of scientific uncertainly, has been a prominent feature of both the tobacco and climate change struggles.

How can we make sound, rational policies in the face of scientific uncertainty? The answer is that we do it all the time. We make decisions about public health, security, and agriculture policy commonly before the science base for these decisions is in. Genetically modified crops and farmed fish were introduced to use before we knew their effects on wild populations. Policy-making and scientific study typically proceed in parallel.

In the 1960s good evidence was available that cigarette smoking causes cancer. This conclusion was actively contested by the tobacco industries in a well-funded long-term campaign of denial well described in Orestes and Conway’s recent book, Merchants of Doubt (2010). Many thousands of lives would have been saved if the industry had not abused scientific uncertainty and manufactured doubt so successfully.

What is interesting about the campaigns of manufactured doubt is that the same cast of contrarian scientists and corporate-funded public relations firms has been involved in opposition to precautionary policy-making in tobacco, most recently second-hand smoke, the ozone hole, toxic chemicals, and climate change. David Michaels in his book Doubt Is Their Product: How industry’s assault on science threatens your health (2008), amply makes the case that industry has turned what should be a debate over policy into a debate over science. The abuse of scientific uncertainty is a clear endangerment of the public’s health. In Dr. Michaels’ words, “It is time to return to first principles: use the best science available, do not demand certainty where it does not and cannot exist.”

The tobacco story has obvious lessons for current efforts to reduce exposure to toxic industrial chemicals and to control greenhouse gas emissions. I would suggest that scientists and health professionals in particular seek to actively:

1.      Understand and defend sound science.

2.      Identify and expose the deliberate manufacture of doubt.

3.      Support the use of the precautionary principle in policy and regulatory decision-making.

4.      Participate in improving science education in elementary and high schools.

5.      Encourage socially responsible actions (including 1-4 above) of scientists and health professionals including themselves.

Study of the nature of science and the scientific process is an academic sub-specialty. In Return to Reason (2001), a recent essay by philosopher and historian Stephen Toulmin provides a useful introduction. A few of the practical elements of sound science can be readily identified: peer review and confirmation, expert review and compilation, full acknowledgement of sources of funding and other potential conflicts of interest. Sound science is peer reviewed, fully assessed by authorities in the field, and confirmed by additional studies.

Peer review is the process of judgment conducted independently by fellow scientists. In the US peer review occurs at three points in the conduct of a particular study: first when a scientist’s proposal is submitted to a government agency, philanthropy, or corporation for funding. Corporations do conduct high quality research but the suspicion exists that corporate review of proposals and topics chosen for study in new research is potentially less objective than review by independent funders.

Peer review occurs next when completed research is submitted for publication. Editors now require but commonly do not get full disclosure of funding sources and potential conflicts of interest e.g. ownership of stock in the company manufacturing the drug or device being studied. Corporate funded research published in non-peer-reviewed journals should be viewed with suspicion of unacknowledged bias.

Sound science is a self-correcting process in which studies are confirmed by repetition and by related studies with alternative methods and design. Studies not subjected to these review processes and confirmed by continued study must be viewed with some degree of suspicion.

Review articles published in peer reviewed or authoritative journals provide yet another independent peer analysis of a body of science. The Annual Review series is a good example. Reviews are a useful guide to sound science in a particular science topic. Reviews are also conducted by expert organizations such as the US National Academy of Science and the Institute of Medicine. The IPCC is the review body for climate science. The IPCC does not conduct research but rather assembles, analyzes and draws conclusions from thousands of science journals from around the world.

It is only the most extreme doubters and deniers who find it possible to believe that all these processes are a hoax. Events like “climate-gate” actually reveal the strength of the process by identifying one or two instances in which non- peer-reviewed publications with erroneous conclusions made it through the IPCC process.

With some of the criteria of sound science in mind, manufactured doubt is not difficult to recognize. Science that is not independently funded after a review process, not published in peer review journals, not cited in review articles or included in publications of national and international scientific bodies is likely not sound science. Because of their training and knowledge, scientists have a special responsibility to publically critique opinion based on such sources.

Use of the precautionary principle is a sound and widely accepted approach to the question of scientific uncertainty. The precautionary principle says that decision-makers have a duty to take preventive action to avoid harm before scientific certainty has been established. The principle is commonly invoked in international environmental and public health treaties and agreements. Essays in Raffensperger, Tickner, and Jackson’s book, Protecting Public Health and the Environment: Implementing the precautionary principle (1999) offers many examples of the use of the principle.

Finally, the whole scientific enterprise will suffer if we do not raise the level of public understanding of science and better train future generations of scientists. President Obama’s Council of Advisors on Science and Technology (PCAST) has very recently released a report on urgency of the problems of science, technology, engineering, and math (STEM) education and a plan to address them. We in the health sciences are particularly able to contribute example and inspiration to students at many levels. Our participation in the science preparation of citizens and future scientists is a critical contribution to the future of sound environmental and health policy.


1.      Stephen Toulmin, Return to Reason. Harvard University Press, Cambridge MA 2001

2.      David Michael, Doubt Is Their Product. Oxford University Press, Oxford 2008

3.      Naomi Oreskes and Erik M. Conway, Merchants of Doubt. Bloomsbury Press, New York 2010

4.      Carolyn Raffensperger, Joel Tickner, and Wes Jackson, Protecting Public Health and the Environment: Implementing the precautionary principle. Island Press, Washington 1999.


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