So this appeared on a facebook thread –

I feel cheated.
I adapted my lifestyle to make it as low carbon as I could. I voted for parties who would take action on climate change. I even directly campaigned against polluters.
And now the methane gas fields in Serbia are thawing. I was told this is the point of no return.
Does anyone know how quickly we will see things go catastrophically bad? And what does that look like?

and I replied

There are multiple overlapping points of no return – the Arctic death spiral (with albedo loss as a positive feedback loop), the loss of the Amazon etc. Anyone who tells you when it will go catastrophically bad is mistaken. There are better scenarios for HOW (agricultural collapse, war, pandemics etc). In terms of how quickly – it could slowly ratchet out over 20 to 50 years, or it could all go tits up in the space of one to four, with overlapping and mutually reinforcing crap. Remember, it’s not the biophysical processes on their own that matter, but the impact they have on human physical and psychological/economic/military/political infrastructures.
If you’d told someone in Vienna in early 1914 that 5 years on the Austro-Hungarian and Ottoman empires would be gone and the commies in charge of formerly-Tsarist Russia, they would have had trouble believing you. In terms of speed. Well, also think Western Europe in 1346 and 1351. About a third of the population dead.
Most of all, remember that what matters is not just the physical processes, but the sense of hopelessness and despair that will soon be upon us, when the scientists shrug their shoulders and say “defo 4 degrees by 2050”. Who will save for a pension? Who will slog for years to become a neurosurgeon etc?