Gases contract when they get cold. If you are doing a yeast diy or one of the ractors from the store with the packets for charges, the CO2 production will be slowed but will probably last a bit longer. With yeast, being a live organism, it slows down and gets "sleepy" with the cold. Bakers use this to their advantage when proofing dough (with heat) and when keeping it for later use (with cold). This prevents the yeast from devouring all the natural sugars found in the starch.