I suspect the warming climate will alter rainfall patterns and global agriculture will be severely disrupted. Industry will suffer as a consequence, and economies will collapse. War, civil conflict and mass migrations will result. Hopefully, global thermonuclear warfare will be avoided, but limited local nuclear conflicts may still erupt sporadically. Democracy will end. Only authoritarian and Fascist/Communist regimes will survive. DO not fantasize about a rural, bucolic or pastoral existence. Look for a return of the city-state, and Feudalism will make a comeback. We'll all be peasants.

The biosphere will be severely affected with many species going extinct and familiar environments modified past the point of recognition. Coastal areas will be flooded and continental interiors will be subject to desertification and abandoned.

I don't expect a collapse of world civilization, but there will be mass mortality, and we'll see cannibalism on a global scale. The world will slide back technologically, to a third-world level, and perhaps even to nineteenth or eighteenth century standards. The most successful and stable countries will resemble modern day Bangla Desh. Places like India, with village based cultures, will be most likely to survive. In general, the climate in any particularly location will resemble the current climate at ten degrees of latitude closer to the equator.

Populations will collapse, and large parts of the world will revert to wilderness. But it wont be a stable wilderness ecosystem that has evolved to adapt to a particular region. It will be a chaotic
and tumultuous battlefield where introduced, non-native species struggle and bloom against each other with little ecological balance or control. We can see places like this already, the Everglades, West Texas, most of Australia. The seas will become deserts, except for a handful of species.

The situation will eventually stabilize as the destruction of human activities eventually lowers CO2 levels. But the environmental deterioration will continue long after the civilization collapses. There will be a lag time. The natural world won't look that much different, except to a naturalist. But the human environment will be almost unrecognizable. The world will become like Central America, or Tibet, or SE Asia.

It won't be a total disaster, but it will take us centuries to recover to even 20th century levels, and many of the resources we'll need to do so will no longer be available at new, reduced levels of technology, organization and finance. The surviving cities will become mines for metals, glass and building stone because we will have forgotten how to make our own. For example, there may still be plenty of oil in the ground, but we won't have the techniques to locate and drill for it. We will burn asphalt for fuel instead.

And worst of all, as we do recover, rather than an enthusiasm for rebuilding our future our scholars (like in the early Middle Ages) will be obsessed with the Golden Age we let slip through our fingers. The next Renaissance will be a long way off.