For a start, all animals, such as cows, pigs and sheep, always gas limed methane, which is the second most common green house gas after carbon dioxide.
But it gets even better, as the oxygen of the air bubble runs out, new oxygen diffuses into the bubble from the water around, it while the carbon dioxide diffuses outwards into the water.
Large fruit eaters such as this one spread the seeds of tropical hardwood trees in their dung, helping to build up forests, which absorb carbon dioxide from the atmosphere.