Abnormal deviation of CO2 from ideal gas behaviour
When the compressibility factor z for CO2 is expressed in terms of reduced pressure and reduced temperature (i.e., using the law of corresponding states), the PVT behavior of CO2 is not very different from that of other gases.  The reduced temperature and reduced pressure are defined as the actual pressure and temperature normalized in terms of the critical pressure and critical temperature, respectively.  The real question is, "what causes the critical temperature and critical pressure of CO2 to be what they are?"