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‘Reasonable doubt’ on climate change is killing the planet

Honest climate scientists acknowledge the limits of their research. Trump and others are cynically exploiting their integrity.

Tthe California fires, floods along the Atlantic coast, the expanding reach of diseases like Zika, and other similarly worrisome events keep sending us signals that the climate system is acting on us, whether we are willing to respond or not. Noah Berger/AP

ON NOV. 23, THE Friday after Thanksgiving, the Trump administration released a report it hoped would pass unnoticed: the Fourth National Climate Assessment — a 1,656 page document, jointly produced by 13 agencies, that lays out what the US government knows about the future of the country and the planet.

The story this report tells is blunt, unequivocal, and terrifying. Given “continued growth in emissions at historic rates, annual losses in some economic sectors are projected to reach hundreds of billions of dollars by the end of the century — more than the current gross domestic product of many US states.”


Worse yet, the report warns, the harms that the United States faces aren’t limited to the most obvious risks — rising sea-level flooding coastal towns, for instance. Instead, the dangers compound, and know no borders: “the full extent of climate change risks to interconnected systems, many of which span regional and national boundaries, is often greater than the sum of risks to individual sectors.”

A growing list of woes runs through the assessment, driving home its central theme: If we continue business as usual, America will lose lives, wealth, and power. The inference is obvious. To avoid the worst, the United States and the world must take significant action now to slow an imminent global environmental disaster and mitigate its overall impact.

Not everyone agrees with that conclusion, of course. The attempt to bury the report in the holiday weekend is just one way President Trump and his administration seek to avoid confronting climate change.

This latest attempt to obscure the case for action on climate change wasn’t wholly successful. This newspaper placed its story on its front page. The well-staffed and experienced climate desk at The New York Times has been covering the report and related stories almost daily since the document’s release.


More broadly, climate change and its dangers have been above the fold a lot lately, most recently in a flurry of stories about a study that explores the conditions that drove the “great dying,” the destruction of most life on earth 250 million years ago. Current polling suggests that the American electorate is taking the danger seriously, with two-thirds of those surveyed concerned about the National Climate Assessment. In response, opponents of climate action are trying an all too familiar tactic to move public opinion back in their direction.

In essence, they’re turning science against itself. They’re treating climate researchers’ willingness to acknowledge the limits of their findings — as all reputable scientists do — as evidence of lingering doubts that relieve us of any obligation to address the problem at all.

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THE TERM “REASONABLE doubt” is woven throughout American civic identity. Most of us hear it for the first time in grade school as a point of pride in the American justice system. In law, reasonable doubt is a very high bar. After our school days, though, most of us don’t go on to become lawyers, and what we think we know about the courtroom comes mainly from TV. In legal dramas from “Perry Mason” to “Law and Order” and beyond, defense attorneys push every discrepancy, large or small, to persuade a jury the real truth remains hidden. When they succeed, fairness and the independent reason of twelve ordinary people demand that the accused walk free. (Real-life lawyers sometimes make similar arguments. “If it doesn’t fit, you must acquit,” defense lawyer Johnnie Cochran famously said of a glove during OJ Simpson’s murder trial.)


Whatever the value of “reasonable doubt” in a criminal trial, it’s an impossible standard when deployed at the intersection of science and politics. Indeed, a weaponized version of the “reasonable doubt” framework threatens civic debate and — when a scientific result is important for human well being — the safety and security of America’s inhabitants, and the world.

This pathology has been on full display as the administration and its allies have tried to defang the new climate report. Reasonable people, they claimed, can still disagree about its conclusions. Former senator Rick Santorum led off, appearing on CNN on the Sunday after Black Friday. He played the role of the defense attorney impeaching the prosecution’s witnesses. Those who wrote the report were, he said, “people who are in the bureaucracy. . . not Trump appointees.” These federal employees, he argued, were in it for their paychecks: “If there was no climate change, we’d have a lot of scientists looking for work,” he said, adding, “a lot of these scientists are driven by the money that they receive.” You can’t trust the Climate Assessment, that is, because the federal bureaucracy is corrupt.

The next day and the day after, President Trump amplified that message of doubt, telling The Washington Post that “a lot of people like myself, we have high levels of intelligence, but we’re not necessarily such believers.” He then offered a rationale for such skepticism. Scientists have said different things at different times, so it’s impossible to come to any conclusion: “There is movement in the atmosphere. There’s no question. As to whether or not it’s man-made and whether or not the effects that you’re talking about are there, I don’t see it — not nearly like it is.”


Think twice, in other words: scientists contradict themselves, there are two sides. . . and hence it is necessary, even prudent, to withhold judgment, to refrain from action, to accept that it may be that humankind is not guilty of changing the climate — and that at a minimum, the climate change predictions are not proven, and any clear verdict must wait for further evidence. In the meantime, steady as we go.

To be sure, Trump and company did not invent this rhetorical approach. As Harvard historian of science Naomi Oreskes and her co-author Erik Conway document in their book “Merchants of Doubt,” those minimizing the risks of climate change are mimicking preceding campaigns like the tobacco industry’s attempt to discount the connection between smoking and lung cancer. Vaccine opponents have employed similar approaches — as, for example, when anti-vaccine activist Robert Kennedy, Jr., in an interview in 2017, accused vaccination advocates of “corruption” and asserted that “industry people have been brought in to essentially dismantle public protections.” Never mind that Kennedy’s claim that “mainstream science” supports his argument is precisely false; as with Santorum’s assertion that climate change researchers are in it for the money, the effect is to provide a pretext for ignoring a broad scientific consensus.


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THE IMMEDIATE ISSUE with such tactics is that they do immediate, direct harm. Smoking does cause cancer, vaccines are safe and life-saving, and climate change is happening, with some consequences already apparent and more profound ones to come. Planting seeds of doubt in the face of settled science on such questions has a direct impact. People get hurt, some die, resources go to waste. But there’s a more lasting risk: the steady erosion of the power of scientific inquiry to inform American politics.

Science is particularly vulnerable to such pleading because of another popular cultural myth: that science is provisional, and often wrong, in the sense that every scientific explanation is incomplete and subject to correction when new information emerges. This myth has the virtue of being true. If nature says “no” to planets traveling in perfectly circular orbits, then no amount of pleading will make it so, and it falls to Isaac Newton to transform ideas about gravity with a new mathematics that describes how planets trace their elliptical paths.

Such wholesale revisions of what experts believe to be true have happened since that first modern scientific revolution. Researchers make mistakes all the time. Outsiders — such as the archetypal rebel, Albert Einstein, whose theory of gravity supplanted Newton’s — can see what the establishment fails to recognize. And the least discrepancy can, sometimes, point to a major shift to come. Science is never finished; the possibility of radical new understanding is always there.

That’s at once accurate — and subject to malicious distortion. The key to the rhetoric of those seeking to discredit the latest findings on climate and vaccines and all the rest is that you can’t be sure of the science; it might change, and if or when it does, then everything scientists claim to know now about the earth’s climate will turn out to be wrong. But insofar as science is genuinely a work in progress, discovery does not work that way.

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THAT’S WHAT THE story of gravity reveals. At first look, it appears to tell a tale that seems to prove that skeptics are absolutely right to say science is contingent, subject to sudden and thorough revision. In 1687, Newton’s gravitation theory decisively demonstrated that nature obeys mathematical laws. His successors used that theory for the next two centuries, mapping the cosmos with ever-finer precision. But then, in the mid-nineteenth century, one stray fact emerged: the orbit of Mercury wobbles just a little more than Newtonian physics says it should. It was a very minor discrepancy, and for a time it was largely ignored — until Albert Einstein, for his own reasons, began to think about gravity. When he completed his general theory of relativity, it perfectly accounted for that tiny excess of Mercury’s motion — a result that was the first confirmation that Einstein’s account of gravitation was correct and that Newton’s was wrong.

Told that way, it appears that when, for example, a series of satellite observations appears to contradict other data in the climate change debate, Ted Cruz is on solid ground when he argues that climate change science is far from settled, and that the theory behind global warming could collapse.

But look more closely at the safely apolitical concept of gravity. In the century since Einstein’s relativity supplanted Newtonian gravitation as the most accurate account of time, space and motion in the universe, Newton’s math still works to account for an awful lot of experience — including most applications at a human scale. The Apollo missions carried astronauts to the moon on trajectories that were mapped with Newtonian calculations. Gravity certainly tugs on a bridge or a skyscraper, but when you’re designing one, general relativity doesn’t matter; Newtonian mechanics certainly does. The planet Neptune, whose discovery was predicted by a purely Newtonian argument, is still out there, traveling the path the older theory demands. Humans did not need relativity to find it.

Einstein’s theory is genuinely more complete than Newton’s. It is a better, more accurate description of reality. But the two ideas only produce different results under very particular circumstances. Everything the older framework handled correctly it still does — which is why engineers almost never have to think in relativistic language.

As for gravity, so for inquiry more generally. Science is not contingent. Everything that was working just fine doesn’t disappear with each new observation. It is, rather, iteratively provisional — a process in which new findings expand on and correct earlier ones, rather than supplanting them in toto. That’s why, despite Mercury’s errant path, Neil Armstrong still made it to the moon. It’s also why suggestions that scientists are on the take, or that satellite data contradicts sea surface sensors (one of Cruz’s lines), or that smart people don’t believe in climate science are not in fact genuine refutations of the overwhelming and still-growing body of evidence that climate change is real, caused by humans, and poses an increasingly dire threat to American and global well being, peace, and security.

Hence the danger to democracy in the tactic that substitutes familiar courtroom-drama tropes about reasonable doubt for the overwhelming scientific evidence for human-caused climate change. As rhetoric, appeals to uncertainty retain great power. The lie on which they depend — that the always incomplete stories scientific research tells are so fragile that they cannot guide action — is one that, too often, isn’t obviously false to the public at large. That is one of the major reasons why national action on climate change has been so hard to sustain.

In criminal cases, explanations of what “reasonable doubt” means often include a reminder that such reasoned skepticism doesn’t mean that a case has to be proved beyond all doubt. In the public debate on climate change, those who oppose responding to the threat have finessed that caveat to claim that, without some absolute proof of the danger — a direct chain of causation that connects more carbon dioxide in the atmosphere to drought, and from there to the fire that began outside of Paradise, Calif., for example — we still don’t know enough to act.

And yet the California fires, floods along the Atlantic coast, the expanding reach of diseases like Zika, and other similarly worrisome events keep sending us signals that the climate system is acting on us, whether we are willing to respond or not. Scientific versions of the “if it doesn’t fit, you must acquit” argument have worked for years, in many settings. It falls both to the scientists at work in areas that have fallen prey to controversy — and the news media that covers both science and politics — to make it clear what is truly known, and why it matters.

Correction: An earlier version of this piece misstated the timing of a mass-extinction event. The “great dying” occurred 250 million years ago.

Thomas Levenson is a professor of science writing at MIT and an Ideas columnist. His latest book is “The Hunt for Vulcan.”