My horizon for civilization collapse is "probably not before 2030".<p>The most likely scenario I perceive is heavily populated tropical and subtropical areas becoming uninhabitable, initially via failure of subsistence farming, leading to mass migration, and rise of fascistic governments in temperate regions in reaction. Fascistic governments characteristically start wars. Wars in the presence of other fascistic governments spiral out of control, ending meaningful global commerce and triggering global economic collapse. Spiraling war tends toward thermonuclear exchange.<p>All this happens well <i>before</i>, e.g., significant ice sheet collapse, or climate-caused loss of temperate-zone agriculture.<p>Given global economic collapse, CO2 production might fall off as extraction and delivery are disrupted, but processes already begun would take long to wind down. Thus, ocean acidification might still collapse fisheries and eliminate major protein input for whole regional populations. Fisheries anyway depend on reliable fuel delivery.<p>We see hints of all of the above already, with massive migrations to Europe attempted from southerly countries where climate stresses have released forces that tend to civil war; and falling fishery yield. Numerous separate phenomena all produce waves of refugees, whether water stress, declining ag yield, or even migration from immediate neighbors that exceeds already stressed local carrying capacity.<p>Fascistic governments are gaining in all regions; the US's step back must be counted as a blip, as very nearly half its population voted for continuation, and their elected representatives even tried to force the issue.<p>My question is not, how can we slow global climate disruption; it is, how can we prevent near-term global civilizational collapse? Collapse does not seem like the best way to reverse climate disruption, presuming it would even work.<p>If methane clathrates and permafrost carbon are released by (already well begun) local extremes of arctic warming, or loss of sea ice reduces albedo, falling industrial CO2 might not slow temperature rise or ocean acidification. Global nuclear fallout, "nuclear winter", and vaporized industrial base would make any sort of recovery difficult and slow, over decades or even centuries.