What is the temperature at which carbon and oxygen nuclei would split from oneanother in CO2?

Carbon gas would probably does not exist in the atmosphere. But you should be able to split CO2 without photosynthesis.What is the temperature at which carbon and oxygen nuclei would split from oneanother in CO2?
The temp is about 2000 Degree C


But it is easy to slit CO2 via UV radiation and thats the reason why a ribbon of Mg continues to burn even in the presence of CO2 gas because


Burning Mg radiates UV rays and high temp may also attribute to it