This figure shows the predicted distribution of temperature change due to global warming from Hadley Centre HadCM3 climate model. These changes are based on the “business as usual” projections of carbon dioxide and other greenhouse gas emissions during the next century. The plotted colors show predicted surface temperature changes expressed as the average prediction for 2070-2100 relative to the model’s baseline temperatures in 1960-1990. The average change is 3.0°C, placing this model towards the low end of the Intergovernmental Panel on Climate Change’s 1.4-5.8°C predicted climate change from 1990 to 2100. Figure prepared by Robert A. Rohde for the Global Warming Art project.
The number of skeptics of the global warming hypothesis is growing. In spite of increasing evidence for global warming, from January 2007-April 2008, the Pew Center reported a drop of 6 percentage points (from 77 to 71%) of “Americans [who] say there is solid evidence of higher global temperatures.” Disturbingly, this seemingly scientific issue has become politicized. Pew attributes most of the overall drop to Republicans, whose acceptance of global warming has dropped to only 49%, compared with 84% among Democrats and 75% among Independents.1
Strangely, a lack of expertise in the climate change field does not temper the confidence of skeptics who challenge global warming. Students are challenging teachers; talk-radio hosts are challenging scientists; and politicians are labeling the issue a hoax. The media, in a misplaced effort to be balanced, often interview equal numbers of scientists on either “side,” which reinforces the incorrect impression that there are equal numbers on each side.
How should the public interpret this apparent debate? How should teachers respond when challenged? Most teachers and scientists recognize that they lack the expertise to mount a technically robust rebuttal, but if we do not want to concede the argument to those with the biggest megaphones, we must respond in some manner.
- Should we cherry-pick data that will respond to, point-by-point, a student’s tendentiously selected data?
- Should we offer a polemical response, trading an eye-for-an-eye with the critics?
The first option is the strategy favored by the global warming deniers and does not honor logico-deductive reasoning; the second is emotion-based and decidedly, nonscientific. Both approaches are weak intellectually and unsound educationally. Is there an alternative that offers a more general and productive way of thinking about and evaluating global warming, and perhaps, other complex and controversial science?
Futuyma’s recently articulated ‘greatest challenge to science’ helps frame an alternative: “Scientists need to convince people that we have developed honest procedures for understanding how the world works, that we can put confidence limits around most of our conclusions, and that our track record shows we have achieved reliable, if still incomplete, knowledge”.2 Perhaps a deep understanding of the nature of science itself, and a reliance on its processes and products, rather than immersion in gory experimental details, is a better way for the lay public (in fact, any non-expert) to think about complex, cutting-edge science.
Many fields, such as evolution, genetically engineered foods, and nuclear-waste disposal, might benefit from this approach, but given the controversy around global warming, it serves as a particularly current and useful illustration.
Climate science is a multidisciplinary field that involves research in ecology, chemistry, geology, glaciology, meteorology, atmospheric science, marine biology, volcanology, computer modeling, and many other disciplines.
Few people—including scientists, who do not specialize in climate science—are qualified to tackle the technical issues in all these areas—at least in any depth.
Alternatively, we might structure teaching about global warming around just a few nature-of-science style questions.
Is intuition a substitute for science?
First, we must discard one common but often faulty guide to critical thinking: intuition. The weakness of intuition is easier to recognize than to eliminate, but reviewing some examples will help.
- It certainly seems intuitive that the sun rises in the east and moves around the Earth, but it is not true.
- It seems impossible that the DNA in the cells of a single human is sufficiently long that it could—if unraveled and stretched end-to-end—reach the sun and back at least a dozen times, but that is true.
Of those people who deny global warming, many find it hard to believe that “small” changes in anthropogenic carbon dioxide could cause big problems for the planet. After all, it makes up so little of our atmosphere that its concentration is measured in parts per million. The global climate is affected by so many interrelated factors, however, that intuition does not reveal the importance of any single factor. Logical thinking is a skill that must be learned and practiced. Intuition is a poor substitute and an unreliable guide for understanding many things—including nature.
What is science?
Science is the most objective method we have for investigating the natural world, but it does not establish certainty and absolutes. It leads to scientific knowledge that is tentative and incomplete, but consensus develops around well-supported hypotheses, which generally become stronger over time. Science operates within a framework of methodological naturalism—that is, explanations of observable phenomena are limited to the natural world (i.e., no magic allowed). Science is idealized often, but two of its characteristics are crucial here:
- replicability, i.e., using well-accepted experimental systems and procedures
- peer review and publication
Science is not perfect, but it is self-correcting over time because other experts critically examine the work of colleagues and challenge weaknesses in methods and conclusions. (An excellent review by Allchin discusses error and science in more detail.3) The public may not like science, but they know it works. If they did not, they would never fly in a plane, take a prescription drug, or use a cell phone.
As objective as science strives to be, it is not isolated from or immune to social forces and values. Communism cost the former Soviet Union the better part of a generation’s worth of advancement in genetics under the pernicious direction of Trofim Lysenko, who tried to force nature to adhere to ideology. Nature did not comply then to accommodate political or economic objections—and it will not comply today. Science does not create nature’s workings; it merely uncovers and explains them.
- Outside one’s discipline, a scientist is not much different from a nonscientist in terms of specialized knowledge; however, the scientist knows how science is done.
- When scientists with expertise in one area want to understand the work of their colleagues in other disciplines, they are necessarily dependent on review articles and the consensus opinions of experts.
Is there consensus?
So what does the consensus opinion of experts in climate change suggest?
Naomi Oreskes reported as far back as 2004, in Science that scientific consensus was undeniable.4 Her team analyzed 928 abstracts published in scientific journals between 1993-2003 that were identified in databases using the keywords ‘global climate change.’ As she summarized her analysis for the Washington Post, “Seventy-five percent of the papers either explicitly or implicitly accepted the consensus view. The remaining 25 percent dealt with other facets of the subject, taking no position on whether current climate change is caused by human activity. None of the papers disagreed with the consensus position. There have been arguments to the contrary, but they are not to be found in scientific literature, which is where scientific debates are properly adjudicated.”5 This final point is important.
There is also the opinion of the International Panel on Climate Change (IPCC), which issued its fourth assessment report in April 2007 (see Figure 1). One of the conclusions in this report is “A global assessment of data since 1970 has shown that it is likely that anthropogenic warming has had a discernible influence on many physical and biological systems”.6 The authors note, in partial support of this statement, that an analysis of 29,000 data sets shows that “more than 89% are consistent with the direction of change expected as a response to warming”.
The IPCC 2007 final synthesis report goes even further, stating: “There is very high confidence that the net effect of human activities since 1750 has been one of warming.”7 In addition, the American Association for the Advancement of Science, The American Geophysical Union, The American Meteorological Society, and other professional organizations have published statements supporting the consensus that human activity is modifying the climate.
The precautionary principle guides much of the public policy throughout the world, and it should clarify our understanding of climate change. It emphasizes that:
Scientific certainty (e.g., cause and effect links for every step) should not be the threshold for taking action that protects public health and the environment—especially when the consequences may be severe.
In the Wingspread Conference formulation, with reasonable evidence of potential harm, “the proponent of an activity [that threatens harm], rather than the public, should bear the burden of proof.”8
The opportunity costs for not acting to prevent harm should be considered along with the costs of acting.
In the light of the current consensus, the precautionary principle suggests that actions to prevent climate change are reasonable.
Is consensus important?
Science increases what we know in the realm of the unknown. As the boundary of the known increases (circle circumference), our ignorance about unknown unknowns decreases. This assumes that the scope of the unknown is finite.
As science increases the “known,” it also increases our awareness of what we do not know—the realm of known unknowns (Figure 2).
Could the global warming hypothesis be wrong? This is unlikely because climate research has established rising temperature over the past century as a well-validated “known” (e.g., hemispheres, oceans, etc.) and one that is not highly prone to error. A known unknown is the extent of future climate change because of warming.
The confidence that we have in any scientific hypothesis is proportional to the breadth and depth of the evidence in support of that hypothesis.
The convergence of many lines of evidence, from many different disciplines, upon a single conclusion (e.g., a warming Earth caused by greenhouse gasses), is a nice example of consilience (“literally a “jumping together” of knowledge,”9 a concept that was helpfully revived by E.O. Wilson10). This greatly strengthens scientists’ confidence in the robustness of the global warming hypothesis. Much of the nonscientific, popular debate (and denial) centers on values and responses rather than facts, for example the importance of jobs for workers in the coal industry.
So, if the consensus of experts is compelling, and ambitious scientific skeptics have not been able to convince their colleagues that they are wrong, does that mean we non-experts should just sit back and accept everything the experts tell us? Of course not, we should remember:
- The relevance of expert opinions is limited to their areas of technical expertise.
Scientists can collect and interpret the data, but the electorate, through the actions of its representatives and other policymakers, must translate those interpretations into policy. Economic, social, and perhaps ethical dimensions to our potential responses should be considered.
Sound evaluation of economic or social policies should be grounded in sound science, but the policies themselves are not the responsibility of scientists.
With regard to policy and climate change, science can also help estimate the costs associated with actions to prevent further warming, for example the cost of mandating better carbon dioxide scrubbers on coal plants.
Who stands to gain from doubt?
This is one of the most important questions to ask when establishing the context for debate about any complex scientific issue. Interestingly, it is often nonscientists or scientists aligned with nonscientific agendas that raise objections to global warming, for example, lobbyists for the energy and automotive industries and groups have generally opposed government regulation.
If these groups raise economic, political, or philosophical objections that have merit, then we should evaluate them critically on those grounds. When nonscientific interest groups disingenuously dress their nonscientific objections in the clothing of science, however, we are correct to voice our doubts. (Consider the evolution/creationism debate. Does anyone believe that some fundamentalist groups are genuinely interested in the “science” of what they call “alternatives” to evolution? The real argument in this case is theological.)
A healthy dose of skepticism will help us remain vigilant against pseudoscientific red herrings that opponents put forward to divert attention from their true goals. In the case of global warming, what is the agenda that justifies efforts to cast doubt on the consensus claims? If global warming becomes widely accepted, some of the consequence may be that:
- federal and state governments might establish more emissions regulations; and
- industries that emit large amounts of carbon dioxide might be required to invest in cleaner technology, etc.
Critics with a stake in those positions have political and economic motives to resist the conclusions of global warming experts.
Of course, the strength of an alternative scientific hypothesis is not diminished by the mere motivations of its proponents. If global warming is not occurring, or it is independent of human activity, then the data will support that conclusion regardless of who (honestly) gathers and interprets those data. Annual deviations from the general trend of rising temperatures, or recent increases in polar bear populations, etc., nonetheless, do nothing to undermine the global warming hypothesis, just as the absence of any particular transitional fossil does nothing to diminish the strength of evolution.
Where is the claim made? It is also important to ask, where are the objections of critics published and promoted? Venues such as Op-eds, mass-market paperbacks, personal blogs, and radio talk shows are not authoritative or reliable for disseminating scientific information. Similarly, it can be difficult to separate rigorous journals and organizations from those promoted by credentialed scientists but representing hidden interests.
An article critical of global warming, and widely circulated by mail to scientists as part of a petition campaign, was recently published in the Journal of American Physicians and Surgeons.11 If the authors’ analyses and conclusions are sound (namely, that rising carbon dioxide levels are beneficial), why was the article not published in a climate science or ecology journal? Recall Oreskes’ point above about objections that are raised outside the scientific literature.
What should we conclude?
If the consensus of experts is compelling, what are we to make of the much smaller number of genuinely qualified and dedicated climate experts who question global warming, or at least the human contributions to it? They exist and they may do good work, but they are probably (though not necessarily) wrong.
- Many of the current disagreements over global warming deal with long-range predictions, which most climate scientists readily acknowledge depend heavily on the particular models they use, and the accuracy of the input variables.
- In any significant scientific debate, the disagreements of dueling scientists push the discipline forward. Scientists who challenged global warming data a decade ago have driven other scientists to tighten up their experiments—producing even stronger results. Many former skeptics have converted themselves.
A few biologists still claim that HIV does not cause AIDS; they are not nefarious—just wrong. They remain largely ignored because there is no economic driver to amplify their objections, unlike global warming. Charges of a “conspiracy” stifling dissent also fall flat. The history of crank science is filled with examples of “renegades” claiming their revolutionary ideas were suppressed. More often than not, these people are ignored for good reason.
This should be especially good news for teachers who may be challenged by students. Instead, for issues where substantial consensus exists, such as global warming, HIV as the cause of AIDS, and evolution, we may rely on the nature of science itself to bolster our confidence in the consensus view. The history and nature of science are on our side.
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