The rate of change in pH v.s Temperature
You are dealing with temperature variation of carbonic fizzy drinks. So, the situation is somewhat tricky.

Lets approach the problem step by step.


If you raise temperature of neutral water, the rate of decomposition of water will increase. So, the water will contain more protons at higher temperature than at lower temperature, although the neutrality is maintained. Therefore, the pH of neutral water will decrease with temperature. pH of water at 100°C is ~6.126.
Carbonic fizzy drinks contain sodium &amp; potassium bicarbonate salts, which ionize completely in aqueous solution to yield alkali cations &amp; bicarbonate anions. The initial pH is between 3 and 4. (1)
Bicarbonate anion can capture a proton from the system to yield carbonic acid. Carbonic acid is unstable and thus decomposes even at room temperature to produce carbon-dioxide, &amp; thus the bubble! So, even at room temperature gradually the solution turns less acidic, then neutral &amp; finally alkaline. So, here you are not increasing temperature &amp; just letting time to flow, &amp; the pH rises gradually. Therefore, I can expect 'linear relationship between change in pH of carbonic fizzy drinks over time'.
When you raise temperature of carbonic fizzy drinks, the pH increase gets faster because the decomposition of carbonic acid is very much temperature sensitive. It is worthwhile to mention that the rapid pH rise is somewhat countered by the pH lowering due to water's decomposition, but that effect is much less significant as water's decomposition is much less sensitive to temperature. In this case, I can certainly expect deviation from linear behavior (nonlinear or exponential increase) aided by temperature influenced decomposition of carbonic acid.


You may be able to arrive at a mathematical relationship by combining the temperature dependency of carbonic acid &amp; water decomposition.