I heard AOC say recently on a news sound bite (less than a paraphrase) that the 12 year number wasn’t to be taken literally. It was comparable to a Biblical comment like ‘the sheep in my flock here my voice’- not to be taken literally (that is- the saved Christians aren’t really sheep in the way that a cruel heat wave is not really a hater)).
The 12 years was used to symbolize the urgency of correcting Earth ecosphere or atmospheric issues in particular that need be fixed directly or things will get much worse. They say that there is more carbon dioxide in the atmosphere than at anytime in the past 3.5 million years (415 p.p.m.), and the number is steadily rising.