What effect does carbon dioxide in water have on pH levels?

Carbon dioxide (CO2) in water forms carbonic acid (H2CO3) through a reaction with water. This acid dissociates into bicarbonate (HCO3-) and hydrogen ions (H+), which increases the concentration of hydrogen ions in the water. The presence of more hydrogen ions leads to a decrease in pH, indicating a more acidic solution. Thus, the effect of carbon dioxide on pH levels is to lower the pH, making the water more acidic. This chemical behavior is significant in various contexts, including aquatic environments, where carbon dioxide levels can influence the overall health and balance of ecosystems.