The current trajectory of temperature increase is at least 4~5°C (rather optimistic) in 2100, which would mean that a pretty wide area surrounding the equator will, year-round or for significant parts of the year, have a wet-bulb temperature at or above 35°C. It is the limit at which human life (and mammal life in general) is entirely impossible, due to over-heating.
That unlivable area will include most of India, Indonesia, Nigeria, Brazil, etc. Hong-Kong and Taiwan, whether you consider them as part of China or not, will anyway not be livable anymore by then. What do you think will happen when India, a country of 1.3B armed with nuclear weapons, realize it literally has to move somewhere else for survival? Do you think all these people will agree to die in silence, peacefully so as to not inconvenience you?
On top of that grim outlook, agriculture has only been possible relatively recently in human history. Until about 10,000 years ago the climate was not stable enough to reliably grow crops, year after year. That stability is probably already gone. Note that the issue for agriculture (and forests, etc.) is less the actual temperature and more the rain/weather patterns (and evaporation, that links back to temperature).
There is absolutely no guarantee that we will be able to adapt our crops fast enough for agriculture to keep up, especially if there is too much instability around the globe. Without stable crops the number of people that can survive on Earth is not very large. China has recently launched a 'Clean Plate' campaign against food waste. As you can imagine it's not because food is plentiful... but because of excess rain, causing crop failures.
Radioactivity is scary and dangerous in high enough dose. Chernobyl and Fukushima are horrible disasters that should have been avoided, but sadly weren't. But compared to the threat of global warming, risks from nuclear power plants are small, known and manageable. To say it differently, rice from Fukushima may be dangerous, but it's still safer than certain death from lack of rice.
I'm not saying we should be building nuclear power plants everywhere, at all. In any case there's not enough U235 at hand to fill the energy needs of mankind. But I would much prefer we spend fewer resources on closing existing nuclear power plants, and more resources on tackling global warming (looking at my home country, France, and our lignite addicted neighbor, Germany).
Source (in French): https://www.youtube.com/watch?v=xgy0rW0oaFI