I am a scientist who spends a lot of time talking with people about science. I do this because I was inspired early on by Carl Sagan.

Sagan’s books and TV shows, like Cosmos, demonstrated that it’s not just what science knows that is remarkable. Instead, it’s the process that gets us to that knowledge—the process of science—that’s just as extraordinary and deserving of praise.

That’s why I stay in the “science communication” game. And it’s why I spend a lot of time trying to show people what true scientific skepticism really means.

Over the last decade or so, something strange, sad, and very dangerous has happened in the relationship between science and public discourse. Beginning with climate science—though not restricted to it—we’ve seen a sharp rise in a public rejection of science as means to know things about the world. This movement generally goes under the name “denials.” Its followers claim that scientifically-established truths are nothing of the sort.

With climate science, for example, there is usually no single line of reasoning for denial. Some people claim the science is faulty. Some claim there is no consensus, meaning the truths are not “established.” Worst of all, some claim the science is part of a global hoax or conspiracy.

And they all claim that they are not deniers but “skeptics.” But do they know what they’re saying? What does real skepticism mean? What does it take to truly be a skeptic?

Skepticism ain’t easy

The most important thing to understand is that being a skeptic is, first and foremost, a responsibility. It requires something from you—specifically, time … and lots of it. True skeptics are committed to educating themselves on the subjects they’ve decided to become skeptical about. And regarding a topic as vast and complex as climate science, that’s going to be a steep climb.

I’ve often been confronted by people who claim climate science is bunk. After I ask just a few questions, it becomes clear they don’t know even the most rudimentary, high-school level principles of the subject they’re so “skeptical” about. For scientists like me, this means an endless series of playing “whack-a-mole” as the same tired denialist talking points gets trotted out—“the climate is always changing,” “the models don’t make any correct predictions,” “sunspots are the cause of climate change.” If these “skeptics” were willing to put a few hours into reading a freshman textbook rather a random website, such questions would evaporate.

The second most important responsibility for a true skeptic is responding. As I’ve written elsewhere, science is a lot like the blues, a call-and-response kind of thing. If I write a paper you don’t like, then you write a paper challenging my results—then it’s my job to answer that challenge. I can’t just stick my fingers in my ears and chant “nah, nah, nah.”

If I can provide a substantive response to your criticisms, then we move on to the next round. This is literally how science progresses. If I can’t, then my paper falls to the wayside. You can say its been disproven or debunked. What matters is that no one is going to use it anymore in building the scaffolding of knowledge we call scientific understanding (or consensus).

But deniers often quote the same debunked paper over and over again. Case in point: The famous paper claiming a link between vaccines and autism. That paper was retracted by the journal because it was so flawed.  It was literally taken out of the literature. And yet vaccine “skeptics” still point to it as proof of something.

So if you’re not an expert on a subject, can you still be skeptical? Yes, but only with a healthy dose of humility and a willingness to do some work. And there are good resources out there for people. Recently I’ve been reading The Skeptics’ Guide to the Universe by Dr. Steven Novella (with help from others like Cara Santa Maria). It’s a pretty broad book covering topics ranging from cognitive biases to UFOs and intelligent design. While I don’t agree with some of their perspectives, it covers a lot of worthy ground. When it comes climate, I really like the website Skeptical Science. And books like The Madhouse Effect by Michael Mann help explain what denialism looks like.

In the end being a skeptic means being like a scientist and that means being willing to change your mind if the evidence warrants it.

That is what really separates the truth-seekers from the deniers.

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Frank is a professor of astrophysics at the University of Rochester.