Soda from fridge to room temperature
In order to create sparkling beverages, a gas called carbon dioxide (CO2) is dissolved in them, a process that goes under the name of carbonation. 

When dissolved in water, CO2 becomes carbonic acid (H2CO3), following the reaction:

 CO2 (g) + H2O &lt;-&gt; H2CO3    (1)


The double arrow means that the reaction is reversible, that is, you can go from left to right as well as from right to left. So, essentially you have two reactions going on at the same time:

 CO2 + H2O -&gt; H2CO3          (2)


and

 H2CO3 -&gt; CO2 + H2O          (3)


However (and here's the trick) the g next to CO2 means that it is a gas and, as such, is volatile and will leave the water when it is formed (that is why you see bubbles coming out of your soda).

There is a very important law of chemistry called Le Chatelier's principle which states that:


  If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established.


If CO2 was not volatile, what would happen is that, at some point, you would reach a chemical equilibrium, that is, the amount of H2CO3 formed by CO2 dissolving in water would be exactly the same as that of H2CO3 decomposing into CO2. But, as we said, CO2 escapes the water in the form of gas... So what happens is that you are always removing CO2 from your reaction and, as Le Chatelier's principle tells us, the system will react to counteract this loss, by decomposing more carbonic acid to forming more CO2.

This is why, if you pour soda in a glass it will slowly become less and less sparkly, as CO2 will leave the water, be substituted by the decomposition of some more H2CO3 and so on, until no H2CO3 is left.

So, why does a closed bottle of soda stay sparkling until you open it? Simply because CO2 has only a small room to escape (the small empty space on top of the liquid). All I said before works also for a closed can/bottle of soda, but at some point the air on top of the liquid becomes saturated with CO2, that is, it cannot make room for any more CO2. This means that the CO2 will restart to go back into the water.

All of these reaction will be influenced by temperature.
Carbonic acid decomposition is much faster at room temperature compared to 4°C, so what happens is that, at room temperature, reaction (3) will be more favoured compared to (2) and when the can will be opened more CO2 will exit the can, giving you a slightly less fizzy drink. 

This effect is similar to that of shaking the bottle: in that case you are mechanically promoting the dissociation of carbonic acid and helping CO2 to escape from water.

Finally, carbonic acid is, as you may guess, an acid, albeit a very weak one! 

It will therefore contribute to lower the pH of your drink in a more or less strong way, depending on the soda: the pH contribute of H2CO3 will be higher in sparkling water (bringing the pH down from 7 to between 3 and 4) than in Coca Cola, which already contains a strong acid (H3PO4, phosphoric acid) and has a low pH in any case.