The earth has went through several mass extinctions in the past.
The earth was almost completely covered in ice at one point
The earth was almost completely free of ice at one point.
Yet here we are.
Every day there are hundreds of new materials/physics/energy breakthroughs - assisted by ever increasing AI capability. https://phys.org/new...amo-effect.html
Spraying reflective substances into the air is Cro-Magnon engineering. I am talking about new technology.
I am optimistic.
You are simply naïve.
The abovementioned events happened on timescales incompatible with human ones. Humankind can't/won't be interested in waiting 10 000+ years for reversal of sea levels and this can't be fixed in 50 years (what most people max planning horizon is). These processes don't work like that.
The Earth may go through another Ice Age at some point in the future but it won't be due to humans and they certainly can't do anything about it.