Answer:
Volcano erupting (Volcanoes produce massive amounts of CO2)
Natural rain water is slightly acidic (pH = 5.6) since there is carbon dioxide in the atmosphere that dissolves to make carbonic acid.
Explanation:
Trees absorb CO2 rather than releasing it. However, if those trees were to be cut down, massive amounts of CO2 would be released into the atmosphere, so it just depends on the context we are talking about.
