There is about 4.8 grams of CO2 per litre of fizzy drink. A can is 333ml so that’s 1.6g of CO2 per can.
Coke says they sell 1.7 billion servings of coke a day (but not all as cans). Still, let’s say that coke are half the market and that 3.4 billion cans of fizzy drink are sold a day. If all of those cans were opened at once and ALL the carbon dioxide escaped into the atmosphere (in fact a lot of it goes into you) then that’s 3.4 billion x 1.6 g = about 5500 tonnes.
Now, in the atmosphere there is about 3000 BILLION tonnes of carbon dioxide… so even opening 3.4 billion cans at once would only affect the amount of carbon dioxide by about a billionth!