The above phrase reads as if an oxymoron, but “thinking about the unthinkable” is a longstanding policy genre.
First, there is the predictably unimaginable that comes with new categories and convention. Think here of “violent crime” as a legal category in the US that didn’t exist prior to the 1970s. “Speaking of ‘political prisoners’ had become such a major political criticism that it was no longer possible to imagine it as a legal category,” concludes another. That there are ahead new categories and conventions that we don’t imagine is quite predictable.
Second, that there are already existing but different analogies to redescribe current policy problems is also predictable. The Green New Deal has most often been likened to Roosevelt’s New Deal. It’s also been likened to the Civil Rights Movement, 19th century abolitionism, and the war economy of the Bolshevik Revolution. There should be no doubt that the climate emergency has been or will be compared to many other events you and I won’t imagine until that comparison is made.
Third, earthquakes with unimaginable impacts are predicted all the time. That in fact is the genre convention. It’s no more different than predicting that my experience after my death will be the same as my experience before my being conceived.