I love to think about the fact that the graph for CO2 is like this
And we are literally in uncharted territory for how fucked shit will get and how quickly it will go, these types of carbon jumps usually take hundreds or thousands of years, not decades. At present we are about 1.3°C above the baseline 1850, and this will only continue to accelerate until we hit about 3-4°. We have triggered a feedback loop, which at this point seems to be irreversible. More carbon, more methane are inevitable even if we stop all output of these harmful gases at this very moment.
Well nothing really "happens", but more trends we see now will continue and intensify. Think drought, extreme weather including flooding, harsh growing conditions in general. Fires, deforestation, loss of animal life in general, warmer oceans and rising seas.
Uhh not sure what else, theres a lot of questions on how our society will be able to respond to the changes to our understanding of the entire global landscape. Wars may be fought over resources like water. Immigrants fleeing from places now too hot/inhospitable to realistically make a life. How will we respond to life as we know it changing drastically in real time all around us?
If you want the scary answer, read about climate tipping points. I don’t think we’ve really established where they might be triggered but we more likely hit them the more over we get. These are hypothesized catastrophic and irreversible changes