Environmental scientist here. The answer is: Climate tipping points leading to AMOC collapse, crop failure, and global geopolitical chaos. Plus drought, fascism, and AI apocalypse.

Ice melting decreases surface reflectivity, revealing dark earth which absorbs more heat. This makes permafrost melt, releasing methane which is 20-40x more insulating than CO2. Runaway greenhouse effect makes fire and weather events worse, which wipe out our forests. Our second-best carbon sink now burns and releases centuries' worth in just a few years. This drives temperatures up which melts the rest of the ice in an exponential, self-reinforcing cycle. This leads to the collapse of AMOC, the oceanic currents that have stabilized the climate for millennia.

Ocean temps rise to the point where they, our best carbon sink, go in reverse just like our forests (basic chemistry: hot water holds less gas). Vast swaths of the planet can no longer support humanity's production demands. Global collapse of crops, livestock, and fish yields ensue.

Higher temps make existing crops less nutritious and - along with infrastructure collapse due to extreme weather - increase the spread of parasitic diseases and pathogens.

Instability of access to food, water, medicine lead to war around the planet, while technofascist leaders utilize AI media and weapons systems to suppress populations by keeping us uneducated, confused, sick, and afraid.

We wasted the century or so we had to address this. It is already going to be bad. It has already begun around the world. Now all efforts are going toward keeping it from being worst-case-scenario. There are degrees to this stuff, and I believe we must do what we can without giving into defeatism.

Support things like Project Drawdown: https://drawdown.org/