> A critical feature of human physiology is our ability to dissipate internal heat by perspiration. This becomes impossible when the combination of heat and humidity, known as the “wet bulb temperature”, exceeds 35°C. Above this level, we are unable to dissipate the heat generated by our bodies, and the accumulated heat will kill a healthy individual within three hours. Scientists have estimated that a 5.5°C increase would mean that even New York would experience 55 days per year when the combination of temperature and humidity would be deadly (Mora et al., 2017, Figure 4, p. 504).

Honestly, that should be enough to sell the message on its own.

IPCC talks about the plight of the planet, by describing opaque physics and biodynamics processes, as if ordinary people will join the dots, make quantitative scientific appraisals, and selflessly decide to make sacrifices to save the planet.

Most people don't think about the whole planet, or thermodynamics, or the future of humanity. They think about their hip pockets, themselves, and raising kids on a budget.

Renewables are cheaper!

Save money heating and cooling your house with solar energy!

Drive an electric car and save money on fuel and services!

Those are the messages IPCC should be putting out. Everybody loves a bargain. The promise of renewables, once we get over the develop and build cost humps, is infinite bargains. Sell that vista. It's easier than selling science.

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.

All this happens well before, e.g., significant ice sheet collapse, or climate-caused loss of temperate-zone agriculture.

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.

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.

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.

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.

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.

Either way, the earth system will regulate, it would be nice if civilisation managed to survive the transition. I'm pretty sure there will still be humans around, happy humans I'm not so sure.