That happened before too, and has been (at lower frequency) for all of recorded history, near as we can tell. As noted, not an outright catastrophe right now.
The discussion is about avoiding it becoming one, and relative impacts. Humanity isn’t going to be dead tomorrow because of this, but may be in more pain in a decade or two, and longer term even more so.
Regional collapses have happened. This will be the first global collapse.
If it happens, it will be much earlier than you hope, as millions, then tens of millions, then hundreds of millions force their way across borders, and fascist governments ride that into power and then start a global thermonuclear war. The refugees will only be fleeing crop failure and increasingly murderous kleptocratic government.
It is already starting. Lots of governments are flirting with dictatorship, and many have got there already. US and Brazil have drawn back a hairsbreadth from the brink, but for how long?
It is a fact that almost half the US voting population is ready and willing to vote in somebody who would arrange never to leave office. Numerous billionaires support that outcome.
