Today’s March for Science is odd. Marches are usually held to defend something that’s in peril. Does anyone really think big science is in danger? The mere fact that the March was scheduled for Earth Day betrays what the event is really about: politics. The organizers admitted as much early on, though they’re now busy trying to cover the event in sciencey camouflage.

If past is prologue, expect to hear a lot about the supposed “consensus” on catastrophic climate change this week. The purpose of this claim is to shut up skeptical non-scientists.

How should non-scientists respond when told about this consensus? We can’t all study climate science. But since politics often masquerades as science, we need a way to tell one from the other.

“Consensus,” according to Merriam-Webster, means both “general agreement” and “group solidarity in sentiment and belief.” That sums up the problem. Is this consensus based on solid evidence and sound logic, or social pressure and groupthink?

Anyone who has studied the history of science knows that scientists are prone to herd instincts. Many false ideas once enjoyed consensus. Indeed, the “power of the paradigm” often blinds scientists to alternatives to their view. Question the paradigm, and some respond with anger.

We shouldn’t, of course, forget the other side of the coin. There are cranks and conspiracy theorists. No matter how well founded a scientific consensus, there’s someone who thinks it’s all hokum. Sometimes these folks turn out to be right. But often, they’re just cranks whose counsel is best ignored.

So how do we distinguish, as Andrew Coyne puts it, “between genuine authority and mere received wisdom? And how do we tell crankish imperviousness to evidence from legitimate skepticism?” Do we have to trust whatever we’re told is based on a scientific consensus unless we can study the science ourselves? When can you doubt a consensus? When should you doubt it?

Your best bet is to look at the process that produced, defends and transmits the supposed consensus. I don’t know of any complete list of signs of suspicion. But here’s a checklist to decide when you can, even should, doubt a scientific “consensus,” whatever the subject. One of these signs may be enough to give pause. If they start to pile up, then it’s wise to be leery.

(1) When different claims get bundled together

Usually, in scientific disputes, there’s more than one claim at issue. With global warming, there’s the claim that our planet, on average, is getting warmer. There’s also the claim that we are the main cause of it, that it’s going to be catastrophic, and that we must transform civilization to deal with it. These are all different claims based on different evidence.

Evidence for warming, for instance, isn’t evidence for the cause of that warming. All the polar bears could drown, the glaciers melt, the sea levels rise 20 feet and Newfoundland become a popular place to tan: That wouldn’t tell us a thing about what caused the warming. This is a matter of logic, not scientific evidence. The effect is not the same as the cause.

There’s a lot more agreement about (1) a modest warming trend since about 1850 than there is about (2) the cause of that trend. There’s even less agreement about (3) the dangers of that trend, or of (4) what to do about it. But these four claims are often bundled together. So, if you doubt one, you’re labeled a climate change “skeptic” or “denier.” That’s dishonest. When well-established claims are tied with other, more controversial claims, and the entire bundle is labeled “consensus,” you have reason for doubt.

(2) When ad hominem attacks against dissenters predominate

Personal attacks are common in any dispute. It’s easier to insult than to the follow the thread of an argument. And just because someone makes an ad hominem argument, it doesn’t mean that their conclusion is wrong. But when the personal attacks are the first out of the gate, don your skeptic’s cap and look more closely at the data.

When it comes to climate change, ad hominems are everywhere. They’re even smuggled into the way the debate is described. The common label “denier” is one example. This label is supposed to call to mind the charge of columnist Ellen Goodman: “I would like to say we’re at a point where global warming is impossible to deny. Let’s just say that global warming deniers are now on a par with Holocaust deniers.”

There’s an old legal proverb: If you have the facts on your side, argue the facts. If you have the law on your side, argue the law. If you have neither, attack the witness. When proponents of a scientific consensus lead with an attack on the witness, rather than on the arguments and evidence, be suspicious.

(3) When scientists are pressured to toe the party line

The famous Lysenko affair in the former Soviet Union is example of politics trumping good science. But it’s not the only way politics can override science. There’s also a conspiracy of agreement, in which assumptions and interests combine to give the appearance of objectivity where none exists. This is even more forceful than a literal conspiracy enforced by a dictator. Why? Because it looks like the agreement reflects a fair and independent weighing of the evidence.

Tenure, job promotions, government grants, media accolades, social respectability, Wikipedia entries, and vanity can do what gulags do, only more subtly. Alexis de Tocqueville warned of this almost two centuries ago. The power of the majority in American society, he wrote, could erect “formidable barriers around the liberty of opinion; within these barriers an author may write what he pleases, but woe to him if he goes beyond them.” He could have been writing about climate science.

Indeed, the quickest way for scientists to put their careers at risk is to raise even modest questions about climate doom (see here, here and here). Scientists are under pressure to toe the party line on climate change and receive many benefits for doing so. That’s another reason for suspicion.

(4) When publishing and peer review in the discipline is cliquish

Though it has its limits, the peer-review process is meant to provide checks and balances. At its best, it helps weed out bad and misleading work, and make scientific research more objective. But when the same few people review and approve each other’s work, you get conflicts of interest. This weakens the case for the supposed consensus. It becomes, instead, another reason for doubt. Those who follow the climate debate have known for years about the cliquish nature of publishing and peer review in climate science (see here for example).

(5) When dissenters are excluded from the peer-reviewed journals not because of weak evidence or bad arguments but to marginalize them.

Besides mere cliquishness, the “peer review” process in climate science has, in some cases, been subverted to prevent dissenters from being published. Again, those who follow the debate have known about these problems for years. But the Climategate debacle in 2009 revealed some of the gory details for the broader public. And again, this gives the lay public a reason to doubt the consensus.

(6) When the actual peer-reviewed literature is misrepresented

We’ve been told for years that the peer-reviewed literature is unanimous in its support for human-induced climate change. In Science, Naomi Oreskes even produced a “study” of the literature supposedly showing “The Scientific Consensus on Climate Change.”

In fact, there are plenty of dissenting papers in the literature. This is despite mounting evidence that the peer-review deck was stacked against them. The 2009 Climategate scandal underscored this: The climate scientists at the center of the controversy complained in their emails about dissenting papers that survived the peer-review booby traps they put in place. They even fantasized about torpedoing a climate science journal that dared to publish a dissenting article.

(7) When consensus is declared before it even exists

A well-rooted scientific consensus, like a mature oak, needs time to grow. Scientists have to do research, publish articles, read about other research, and repeat experiments (where possible). They need to reveal their data and methods, have open debates, evaluate arguments, look at the trends, and so forth, before they can come to agreement. When scientists rush to declare a consensus — when they claim a consensus that has yet to form — this should give everyone pause.

In 1992, former Vice President Al Gore reassured his listeners, “Only an insignificant fraction of scientists deny the global warming crisis. The time for debate is over. The science is settled.” In the real 1992, however, Gallup “reported that 53% of scientists actively involved in global climate research did not believe global warming had occurred; 30% weren’t sure; and only 17% believed global warming had begun. Even a Greenpeace poll showed 47% of climatologists didn’t think a runaway greenhouse effect was imminent; only 36% thought it possible and a mere 13% thought it probable.”

Seventeen years later, in 2009, Gore revised his own fake history. He claimed that the debate over human-induced climate change had raged until as late as 1999, but now there was true consensus. Of course, 2009 is when Climategate broke, reminding us that what had smelled funny was indeed rotten.

(8) When the subject matter seems, by its nature, to resist consensus

It makes sense that chemists over time may come to agree about the results of some chemical reaction, since they can repeat the results over and over in their own labs. They’re easy to test. But much of climate science is not like that. The evidence is scattered and hard to track. It’s often indirect, imbedded in history and laden with theory. You can’t rerun past climate to test it. And the headline-grabbing claims of climate scientists are based on complex computer models that don’t match reality. These models get their input, not from the data, but from the scientists who interpret the data. This isn’t the sort of evidence that can provide the basis for a well-founded consensus. In fact, if there really were a consensus on the many claims around climate science, that would be suspicious. Thus, the claim of consensus is a bit suspect as well.

(9) When “scientists say” or “science says” is a common locution

In Newsweek’s April 28, 1975, issue, science editor Peter Gwynne claimed that “scientists are almost unanimous” that global cooling was underway. Now we are told, “Scientists say global warming will lead to the extinction of plant and animal species, the flooding of coastal areas from rising seas, more extreme weather, more drought and diseases spreading more widely.” “Scientists say” is ambiguous. You should wonder: “Which ones?”

Other times this vague company of scientists becomes “SCIENCE.” As when we’re told “what science says is required to avoid catastrophic climate change.” “Science says” is a weasely claim. “Science,” after all, is an abstract noun. It can’t speak. Whenever you see these phrases used to imply a consensus, it should trigger your baloney detector.

(10) When it is being used to justify dramatic political or economic policies

Imagine hundreds of world leaders and NGOS, science groups, and UN functionaries gathered for a meeting. It’s heralded as the most important conference since World War II, in which “the future of the world is being decided.” These officials seem to agree that institutions of “global governance” need to be set up to reorder the world economy and restrict energy use. Large numbers of them applaud wildly when socialist dictators denounce capitalism. Strange activism surrounds the gathering. And we are told by our president that all of this is based, not on fiction, but on science — that is, a scientific consensus that our greenhouse gas emissions are leading to climate catastrophe.

We don’t have to imagine that scenario, of course. It happened at the UN climate meeting in Copenhagen, in December 2009. It happened again in Paris, in December 2015. Expect something at least as zany at the March for Science.

Now, none of this disproves climate doom. But it does describe a setting in which truth need not appear. And at the least, when policy effects are so profound, the evidence should be rock solid. “Extraordinary claims,” the late Carl Sagan often said, “require extraordinary evidence.” When the megaphones of consensus insist that there’s no time, that we have to move, MOVE, MOVE!, you have a right to be wary.

(11) When the “consensus” is maintained by an army of water-carrying journalists who defend it with partisan zeal, and seem intent on helping certain scientists with their messaging rather than reporting on the field as fairly as possible

Do I really need to elaborate on this point?

(12) When we keep being told that there’s a scientific consensus

A consensus should be based on solid evidence. But a consensus is not itself the evidence. And with well-established scientific theories, you never hear about consensus. No one talks about the consensus that the planets orbit the sun, that the hydrogen molecule is lighter than the oxygen molecule, that salt is sodium chloride, that bacteria sometimes cause illness, or that blood carries oxygen to our organs. The very fact that we hear so much about a consensus on climate change may be enough to justify suspicion.

To adapt that old legal rule, when you’ve got solid scientific evidence on your side, you argue the evidence. When you’ve got great arguments, you make the arguments. When you don’t have solid evidence or great arguments, you claim consensus.

Adapted from The American and cross-posted from The Stream. This piece has been updated since its original publication.

Dr. Richards is Executive Editor of The Stream. Follow him on Twitter.

Image: © patramansky — stock.adobe.com.