Basically, as above.
CO2 becomes a liquid under two conditions, when it is under enough pressure, or when it gets cold enough.
Once you have a volume of CO2 under pressure, the partial pressure required to keep it liquid fluctuates directly with the temperature. There's a certain threshold where headspace becomes a major role too but realistically, if it's being filled to ~80-90% of rated capacity by *weight* you're pressure will fluctuate directly with the temperature of the tank.
Also, neat fact, if you have a know volume with a known weight of CO2 in a closed system with a pressure gauge, you can accurately measure temperature