Think about forest fires and prairie fires, mostly caused by lightening, mostly natural. How to they contribute to the Earth's atmosphere and global warming. Think about this.
Actually more water in the atmoshere means less CO2. The reason this is so is that water scrubs CO2 out of the air to form carbonic acid, which has a low vapor pressure. This rains to the earth, and is neutralized by the oceans to become fixed as carbonates, i.e, limestone and sea shells.
One big source of CO2 that rivals industrial input are forest fires. This year alone over 3.5millions acres have burnt in the US. If one poured out the world's production of oil, for this year, on that area it would be 1 ft deep. It shows that US forest fires alone can almost compete with emissions due to oil. If we add all the forest fires in Europe, Asia (Siberia), Africa, Austrlia, South America, the rest of north America, this is the real culprit. It is probally responsible for the cyclic heating and cooling that has occurred before humans were around.