[Yeah yeah, I know. I haven’t blogged in ages. I promise it’s because I’m busy with paying work, not because I hate you all.]

One of the hallmarks of crackpottery is to invoke the shade of Galileo. The logic goes like this: “Galileo expressed a radical idea and was punished for it; I have a radical idea that other people don’t like; therefore, I’m like Galileo”. Many of the unsolicited emails and blog comments I get about personal theories — grand unification schemes, claims to have overthrown relativity or quantum mechanics, ancient Earth gravity — use this kind of argument, the implication being that if I reject their ideas, I’m on the wrong side of history.

These emails and comments are mostly from harmless souls. However, Galileo’s name and spirit are sometimes invoked in a more troublesome way. Take, to wit, this excerpt from a piece in the Huffington Post:

“On the global warming alarmists, anyone who actually points to the evidence that disproves their apocalyptical claims, they don’t engage in reasoned debate,” Cruz said in an interview with reporter Jay Root on Tuesday. “What do they do? They scream, ‘You’re a denier.’ They brand you a heretic. Today, the global warming alarmists are the equivalent of the flat-Earthers. It used to be [that] it is accepted scientific wisdom the Earth is flat, and this heretic named Galileo was branded a denier.”

The “Cruz” in this passage is United States Senator Ted Cruz, who announced his candidacy for President this week. Pretty much everything Cruz says about climate change is wrong. He’s wrong on the evidence, which overwhelmingly supports the notion that climate change is real and going to create problems for us all. He’s wrong on flat-Earthers, who were and are a very fringe group that popped up in relatively recent times as a form of blanket science rejection. There’s a common misconception that many people in medieval times believed in a flat Earth, but that’s not supported by historical evidence.

And he’s totally wrong on Galileo, whose conflict with the Catholic Church and science establishment of his day is one of the best-studied events in the history of science. The Church and science of the day did not support a flat Earth. The official view was that Earth was spherical and sitting at the center of creation; in theological terms Earth was a fallen, imperfect place as opposed to the beautiful unspoiled perfection of the heavens. Galileo’s model of the Solar System, while right in its broad strokes, was actually pretty lousy in details: he constrained the planets to move in circular paths around the Sun, which anyone who had studied the problem knew didn’t work. (The orbits are ellipses rather than circles, as Galileo’s contemporary Kepler worked out.)

And nobody branded Galileo a “denier”. Astronomers of the day could rightfully say that their Earth-centered model of the Solar System worked better than Galileo’s oversimplified Sun-centered model, but that wasn’t the reason Galileo was forced to recant. It wasn’t about data: it was about authority, all stirred up in a stew of cultural and political considerations that seem very alien to many of us today. Galileo’s “heresy” doesn’t mean what Senator Cruz seems to think it does: in that era, it didn’t mean “holding an revolutionary opinion”, but “going against Church doctrine in such a way that risks eternal damnation”.

Jay Rosen wrote an extensive piece on how journalists should approach the problem of climate change denial among politicians. I’m not a political journalist; I’m a scientist and science writer. Obviously the issue of climate change intersects these disparate areas in a way very few other topics do. I realize that presenting facts won’t change anyone’s mind — least of all Senator Cruz’ position on climate change — but I care deeply both about the need to understand how science works and the need to do something about climate change, for the sake of future generations if nothing else.

The Earth-centered cosmology failed because ultimately the astronomical evidence favored a Sun-centered Solar System. Climate change — and humanity’s role in it — is overwhelmingly supported by evidence from a wide variety of sources. Senator Cruz would rather reject that evidence, and in that rejection he’s not on the side of Galileo. If I may quote myself:

Geocentrism fell because the evidence didn’t support it, and today Galileo’s views (with significant additions from Kepler, Newton, and modern astronomy) are the establishment. Years of research have bolstered his position, when it could have been overthrown by subsequent observation; it is establishment because the evidence supports it. Climate science isn’t an easy field, but there is overwhelming consensus that global warming is real and human-caused, based on years of research and enormous quantities of data.

The difference is that if we fail to act on global warming, we won’t just have one scientist sitting under house arrest.