Why does warm beer go flat more easily than cold beer?

Warm beer goes flat more easily than cold beer primarily because warmer temperatures reduce the solubility of carbon dioxide in the liquid. When beer is warm, the gas that gives it carbonation is less able to remain dissolved, leading to quicker release of carbon dioxide bubbles. This results in a loss of carbonation, giving the beer a flat taste.

In contrast, cold beer retains carbonation better due to the cooler temperatures keeping more of the carbon dioxide dissolved in the liquid. Thus, enjoying beer chilled helps maintain its fizziness and overall mouthfeel. The other factors listed, such as alcohol content, sugar levels, or acidity, do not have a direct impact on the carbon dioxide solubility as temperature does.