Carbon Dioxide, pH, and ocean acidification

Carbon dioxide and pH - Put a couple drops of phenolphthalein indicator in a flask of dilute (.01M) NaOH.  The fluid should turn pink, indicating the presence of hydroxide ions.  Using a straw, blow into the flask until the pink color disappears.  What affect dos carbon dioxide have upon the pH of the solution?

CO2 + H2O  →  H2CO3  → H+ + HCO3-