For example this curve
View attachment 355180
which shows the total CO2 emission of different vehicle types over their usage.
It should be also said that CO2 emissions don't include the whole environmental and social footprint with also important aspects like the consumption of limited resources and the nowadays in times of EURO 6-7 dominating particle emission from brakes (usually better in EV due to recuperation) and tires (usually worse in EV due to higher vehicle mass).
With this I don't imply of course that EVs are generally worse but as everything in this universe the answer is not simple black or white but a compromise and depends on the individual usage and priorities set.