Observers from various camps call for basing public policy on sound science. Yet, as the understanding of climate science has progressed, the relationship between scientists and government decision-makers has proved both constructive and tortuous.

This history provides several lessons on the potential benefits and pitfalls of using scientific assessments to enact laws and regulations.  Thus, it could have profound implications for the making of policies that protect consumers.

My recent narrative, The Presidents and the Planet: Climate Change Science and Politics from Eisenhower to Bush, describes how the eminent California oceanographer Roger Revelle launched modern climate change science in 1955 with a presentation to the American Association for the Advancement of Science that became the basis of his better known 1957 academic article on the subject.

Before Revelle’s bombshell, scientists paying attention to the issue believed that carbon dioxide trapped heat and that the growing combustion of fossil fuels was emitting a lot of it into the earth’s atmosphere. Most assumed, however, that the carbon dropped back relatively quickly to the earth’s surface, where most of it ended up in the ocean. Revelle made the contrarian assertion that the chemistry of oceans prevented them from absorbing carbon fast enough to keep the atmosphere in equilibrium.

In some ways, Revelle’s theory was as disruptive as the heretical belief of Copernicus and Galileo in the 16^th and 17^th centuries that the sun did not rotate around the earth.

Revelle was a formidable force in American science. He had served as the U.S. Navy’s chief oceanographer during World War II. In the 1950s, he contributed to influential National Academy of Sciences reports and chaired the oceanography panel of the highly publicized International Geophysical Year. Revelle helped find the funding for his colleague Charles (Dave) Keeling to meticulously measure atmospheric carbon. The data ended up supporting Revelle’s views about carbon’s long persistence in the atmosphere. Word of their findings spread in the academic world.

By 1959, Revelle had told a U.S. House hearing about the importance of understanding the science of climate change and the need for federal research funding.

Ignored by historians until recently, Revelle advised John F. Kennedy on three messages, in which the President mentioned the need to understand the interactions between the atmosphere and oceans because they influenced the earth’s climate. Somewhat better known, Revelle wrote a very substantive section on climate change in Lyndon B. Johnson’s historic White House report Restoring the Quality of Our Environment (1965).

Revelle later advised Maine Senator Ed Muskie (the principal sponsor of the 1970 Clean Air Act, which authorized regulation of greenhouse gases by the Environmental Protection Agency), Tennessee Senator Al Gore (his former student at Harvard and later Vice President of the United States), and every administration until he died in 1991.

Revelle was far from the only scientist communicating with the legislative and executive branches. In the 1970s, Wally Broecker, Ralph Rotty, and Gordon MacDonald provided remarkably prescient briefings on the risks of climate change. In the 1980s, James Hansen, Stephen Schneider, Michael Oppenheimer, and Jerry Mahlman were among the many climate experts testifying before congressional committees.

Hearings chaired by Democrats and Republicans alike welcomed the assessments of these scholars, leading to additional funding for climate research and, during Ronald Reagan’s second term, a new Intergovernmental Panel on Climate Change and a global agreement to protect the atmosphere’s ozone layer.

Despite the early access of the pioneers of climate change science to the halls of power, their impact on policy encountered numerous roadblocks. Most notably, not until 2022 did the U.S. Congress pass comprehensive legislation with a primary focus on curbing climate change. The Inflation Reduction Act came sixty-two years after the initial publication of Keeling’s data. Despite the bill’s hefty incentives to reduce greenhouse gas emissions, the need to make it filibuster-proof limited its scope.  Moreover, climate change went unmentioned in the title, and the administration made only feeble attempts to explain its benefits for consumers. Two years later, the bill’s critics took over and raced to dismantle it.

Climate change faces high hurdles on the path to effective political responses:

• Carbon dioxide is a rare global pollutant that affects the entire planet regardless of where it originates. Thus, effective solutions require international cooperation.
• The unusually long persistence of carbon dioxide in the atmosphere (more than a hundred years) means that even dramatic actions that accelerate or slow emissions take a long time to become apparent to the human eye.
• Moreover, nature has its thorny complexities, and climate data are often asymmetric.

In short, the challenge is not one lending itself to quick political fixes.

Still, clearer communication might have spurred earlier policy responses. One obvious barrier to popular understanding of climate change science is most Americans’ unfamiliarity with the metric system, the measurements most common in international and academic circles. Saying the world is on a path to average surface warming of 2.5 degrees Celsius is, technically, the same as 4.5 degrees Fahrenheit. But the numbers sound very different. As a result, American nonscientists might underestimate the risks involved, especially if they don’t understand that averages mask the variable rates of temperature change that lead to, for instance, more violent storms.

In his congressional testimony, James Hansen used Fahrenheit to communicate more effectively with the American public. However, many scientists continued to talk in Celsius, as if public understanding was of little concern.

A more subtle yet substantial barrier to communication is the difference in the definition of “certainty” inside and outside academia. Scientists rarely claim certainty for their findings. This reluctance reflects their humility in understanding there’s always more to be known. As science historian Spencer Weart has pointed out, it also reflects a tendency to produce reports that are more grant proposals than research findings; it is the “uncertainties” that justify the need for additional funding.

An overemphasis on uncertainties to the detriment of explaining what was considered likely to occur was a glaring weakness of pivotal climate change reports by the National Academy in 1975 and 1983. Revelle tried to correct this excessive caution in an Academy report he chaired in 1977. He said that because carbon dioxide remained in the atmosphere so long, waiting for certainty meant that the die would have already been cast if such certainty was ever achieved. Revelle’s overseers at the Academy, not wanting to rock the boat, forced him to tone down his warnings about the risks of climate change.

The Academy’s stance in the 1970s and 1980s followed a frequent pattern, often downplaying climate change’s effects by extolling adaptation strategies that had minimal applicability to less wealthy nations and delaying the public discussion of climate impacts until computers could model them with greater precision.

Although the Academy later became more straightforward in its reports on the effects of climate change, its focus on “uncertainties” provided the cudgel that traditional energy interests needed to defer climate action.

Oil companies and electric utilities had ways to influence climate scientists, whose activities they sometimes funded. However, these businesses became considerably more confrontational after the creation of the Intergovernmental Panel on Climate Change. They financed a group of scientists willing to put their names on articles written by public relations staff claiming the world wasn’t really warming. Their ultimate trump card was that the science was still too uncertain or unsettled to support policy responses.

The vested interests worked hard to cover their tracks, but their impact on public opinion was substantial. Thus, the lack of transparency about some scientists’ sources of funding degraded the quality of the climate change debate.

By the 1990s, climate skeptics had taken over several congressional committees. When a skeptical chair asked a climate scientist whether they were certain about their findings, the scientists, talking in the language of the Ivory Tower, would generally say no. The chair could then move quickly on, satisfied that the case against action had been made.

The dialogue on climate change between scientists and elected officials could have been more productive if scientists had not put so much emphasis on the quest for certainty in their most widely read publications. Vicious attacks from fossil fuel industries would have come in any case. But what the scientists meant would have been more evident and less vulnerable to attack.

In 1989, Jerry Mahlman, director of the geophysical fluid dynamics lab at the National Oceanic and Atmospheric Administration, explained at a Senate hearing why the concept of certainty was not very useful in facilitating clear communication between scientists and nonscientists.  Scientists rarely asserted certainty because it was so rare. Rather than dub almost everything else uncertain, he recommended a focus on levels of probability. He found several basics of climate science as “very probable” or “probable.” He suggested that policymakers also pay attention to other trends with “corroborating evidence” but not enough computer power to reproduce complex natural phenomena. More than a quarter century later, Mahlman’s tutorial for senators provides excellent guidance.

The slow U.S. response to the challenge of climate change is a cautionary tale for policymakers in many areas – from health to consumer and worker safety.

The discussions on these topics often use probabilities as their guiding stars. However, all policymakers need to be wary of claims that scientific findings should be categorized as “certain” or “settled” on the one hand or “uncertain” or “unsettled” on the other.

In most cases, complete certainty is unachievable in the foreseeable future, even if the rosy optimism of artificial intelligence boosters proves correct. Therefore, it is essential to acknowledge that some findings can be uncertain but still very likely.

Policymakers should avoid querying scientists about whether or not they are certain.  Instead, they need the wisdom to focus on what most scientists think is probable or very probable and act accordingly.