Because they are believing something. The Cult of Climate ‘Science’.
Glacier National Part put up signs about 10 years ago, that basically said the glaciers would be gone by 2020. Those signs are being changed.
Notice the slight hedge — “computer models indicate” — in the wording of the now-replaced sign.
Obfuscation? I’m sure they don’t know what that is.
These “models” must be objective, because machines can’t be biased, right? And yet these models were actually developed by human beings like Michael “Hockey Stick” Mann, who has made a habit of suing his critics in an effort to silence them.
“Computer models indicate” is one of those phrases like “according to scientists” which can be made to function as a form of argument from authority (argumentum ab auctoritate), a fallacy that anyone who has taken an introductory course in logic should recognize.
But no one on the Left will notice.