In such a climate, earth would possibly not be able to sustain a large multi-billion human population.
We have already observed several periods in the modern climate era, the Holocene, that have been warmer than modern temperatures with nothing but positive implications for humanity during those times. These periods include the Medieval Warm Period (aligned with the Viking Age and the conquering of Iceland and Greenland), the Roman Warm Period (aligned with Rome's golden age) which saw the Mediterranean as being 2C hotter than modern temps [1], the Minoan Warm period (which was also a boomtime for humanity until the Santorini explosion plunged temperatures worldwide) [2] and of course the Holocene Climate Optimum (about 9000 to 5000 years before present, also associated with booms in human populations in China and elsewhere [3]. In fact, the most devastating events to occur to humans and life on earth tends to be associated with global plunge in temperatures, like the Younger Dryas event just before the onset of the Holocene, that saw temperatures plunge to ice age levels, and is associated with numerous extinctions. Cold episodes in earth's climate are really to be feared. They cause drought, famine, and widespread misery. Warmth and CO2 are good for plants. I hope we continue to warm, but Earth can always revert back into a glacial phase and we are powerless to stop it.
[1] Persistent warm Mediterranean surface waters during the Roman period https://www.nature.com/articles/s41598-020-67281-2
[2] Swedish tree rings provide new evidence in support of a major, widespread environmental disruption in 1628 BC https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1999...
[3] https://www.sciencedirect.com/science/article/abs/pii/S10406...
[4] https://www.sciencedirect.com/topics/earth-and-planetary-sci...