Algae absorb Carbon dioxide in photosynthesis.
Cows produce methane which is 80 x more potent as a greenhouse gas than carbon dioxide.
Volcanoes produce many gases. Mercury is not a gas but chucked out by volcanoes.
rice growing in paddy field also produces methane.
A small increase from 0.03% carbon dioxide to 0.04% can have a dramatic effect on climate.
