Recently two research teams, working independently and using different methods, reached an alarming conclusion: The West Antarctic ice sheet is doomed. The sheet’s slide into the ocean, and the resulting sharp rise in sea levels, will probably happen slowly. But it’s irreversible. Even if we took drastic action to limit global warming right now, this particular process of environmental change has reached a point of no return.

Meanwhile, Senator Marco Rubio of Florida — much of whose state is now fated to sink beneath the waves — weighed in on climate change. Some readers may recall that in 2012 Mr. Rubio, asked how old he believed the earth to be, replied “I’m not a scientist, man.” This time, however, he confidently declared the overwhelming scientific consensus on climate change false, although in a later interview he was unable to cite any sources for his skepticism.

So why would the senator make such a statement? The answer is that like that ice sheet, his party’s intellectual evolution (or maybe more accurately, its devolution) has reached a point of no return, in which allegiance to false doctrines has become a crucial badge of identity.

I’ve been thinking a lot lately about the power of doctrines — how support for a false dogma can become politically mandatory, and how overwhelming contrary evidence only makes such dogmas stronger and more extreme. For the most part, I’ve been focusing on economic issues, but the same story applies with even greater force to climate.

To see how it works, consider a topic I know well: the recent history of inflation scares.

More than five years have passed since many conservatives started warning that the Federal Reserve, by taking action to contain the financial crisis and boost the economy, was setting the stage for runaway inflation. And, to be fair, that wasn’t a crazy position to take in 2009; I could have told you it was wrong (and, in fact, I did), but you could see where it was coming from.

Over time, however, as the promised inflation kept failing to arrive, there should have come a point when the inflationistas conceded their error and moved on.

In fact, however, few did. Instead, they mostly doubled down on their predictions of doom, and some moved on to conspiracy theorizing, claiming that high inflation was already happening, but was being concealed by government officials.

Why the bad behavior? Nobody likes admitting to mistakes, and all of us — even those of us who try not to sometimes engage in motivated reasoning, selectively citing facts to support our preconceptions.

But hard as it is to admit one’s own errors, it’s much harder to admit that your entire political movement got it badly wrong. Inflation phobia has always been closely bound up with right-wing politics; to admit that this phobia was misguided would have meant conceding that one whole side of the political divide was fundamentally off base about how the economy works. So most of the inflationistas have responded to the failure of their prediction by becoming more, not less, extreme in their dogma, which will make it even harder for them ever to admit that they, and the political movement they serve, have been wrong all along.

The same kind of thing is clearly happening on the issue of global warming. There are, obviously, some fundamental factors underlying G.O.P. climate skepticism: The influence of powerful vested interests (including, though by no means limited to, the Koch brothers), plus the party’s hostility to any argument for government intervention. But there is clearly also some kind of cumulative process at work. As the evidence for a changing climate keeps accumulating, the Republican Party’s commitment to denial just gets stronger.

Think of it this way: Once upon a time it was possible to take climate change seriously while remaining a Republican in good standing. Today, listening to climate scientists gets you excommunicated — hence Mr. Rubio’s statement, which was effectively a partisan pledge of allegiance.

And truly crazy positions are becoming the norm. A decade ago, only the G.O.P.’s extremist fringe asserted that global warming was a hoax concocted by a vast global conspiracy of scientists (although even then that fringe included some powerful politicians). Today, such conspiracy theorizing is mainstream within the party, and rapidly becoming mandatory; witch hunts against scientists reporting evidence of warming have become standard operating procedure, and skepticism about climate science is turning into hostility toward science in general.

It’s hard to see what could reverse this growing hostility to inconvenient science. As I said, the process of intellectual devolution seems to have reached a point of no return. And that scares me more than the news about that ice sheet.