Quick—what do all these claims have in common?

• Heat consists of a self-repelling fluid (‘caloric’).
• Danny Shechtman is talking nonsense; there is no such thing as quasicrystals, only quasi-scientists. [Linus Pauling]
• Gastropyloric ulcers are non-infectious in aetiology.
• Proteins are the key to all genetics. (DNA isn’t nearly complex enough to carry hereditary information.)
• The centre of the universe is not the Earth but the Sun.
• The centre of the universe is not the Sun but the hub of the Milky Way, around 40,000 light years away.
• …#climate change is real, man-made and dangerous. Read more: http://OFA.BO/gJsdFp [Barack Obama]
• The worst human beings are outbreeding the best. Only eugenics can stop the rising sea of imbeciles, the dead weight of human waste [Margaret Sanger], ill-trained swarms of inferior citizens [H. G. Wells], Jews, blacks, degenerates [Theodore Roosevelt], the feeble-minded [Francis Galton], criminals and weaklings [Luther Burbank].
• Saccharin causes cancer.

Get it?

That’s right: they all have evidence behind them. A lot of evidence.

In each and every case there is or was a whole body of different measurements piling up and pointing to a single, consistent scientific conclusion. We’re talking hard, physical evidence. From the natural world.

How do I know? Because scientists overwhelmingly agreed on these ideas; they reached what scientists call a consensus /kənˈsɛnsəs/.

That proves it. After all, there is no consensus without evidence. The evidence has to be overwhelming or, by definition, overwhelming consensus can’t occur. But it did occur—scientists agreed—which proves, syllogistically, how much evidence they had.

You don’t believe me.

Perhaps I’m not communicating this as well as I could. You’re skeptical. Fine; don’t take my word for it.

Take science communicator^† John Cook’s word for it:

There are two aspects to scientific consensus. Most importantly, you need a consensus of evidence—many different measurements pointing to a single, consistent conclusion. As the evidence piles up, you inevitably end up with near-unanimous agreement among actively researching scientists: a consensus of scientists.

A number of surveys of the climate science community since the early 1990s have measured the level of scientific consensus that humans were causing global warming. Over time, the percentage of climate scientists agreeing that humans are causing global warming has steadily increased. As the body of evidence grows, the consensus is getting stronger.

Get it now?

Update

A number of readers have asked if we’d accept an alternative answer: “all those ideas are wrong.”

Close, but no. Look again—one of them is actually true.

Hint: History’s first mulatto US President… ninety-seven percent of scientists agree… ringing any bells?

^†John Cook’s science communication work was recognised by the $10,000 Australian Museum Eureka Prize for Advancement of Climate Change Knowledge in 2011.

John is the Climate Communication Research Fellow at the Global Change Institute, University of Queensland, Adjunct Researcher at UQ and Adjunct Lecturer at University of Western Australia.

When he’s not busy teaching Australians about the difference between evidence and opinion and how, in fact, there isn’t one, John runs the SkepticalScience website.