Answer: at higher temperatures.
Justification:
1) Soda have CO₂ dissolved. Carbonation consists on that: dissolving CO₂ into water, leading to carbonated water.
2) The solution of a gas into a liquid is inversely related to the temperature: the lower the temperature the more gas gets dissolved.
So, in the manufacturing of soda, the CO₂ is added in cool water in a cool environment.
3) So, the higher the temperature after the soda is delivered, the more gas will be liberated when you open the can.