H2O is actually a more potent greenhouse gas than CO2.

But the answer to your question in the thread below is “negligible”. Sea level rise comes from melted ice, not from water formed during combustion.

The amount of water added to the world’s total supply by burning hydrocarbons is insignificant compared to the huge amounts already present in the oceans. Even if every bit of oil in the earth was burned overnight, the increase in the world’s water supply would be impossible to measure. And even all that extra water would soon wind up back in the ocean as a liquid, and no longer contribute to greenhouse warming. Liquid water and ice are not greenhouse gases, water vapor is a greenhouse gas. OTOH, CO2 remains a gas, and its sinks (dissolving in the oceans, conversion to vegetation and carbonates) are rapidly becoming saturated. The CO2 formed by combustion is a greenhouse gas; that is the problem, its effect on global warming is because it makes the atmosphere opaque to emitted infrared radiation from the surface.

A similar situation is caused by burning natural gas (methane, also a worse greenhouse gas than CO2). CH4 + 2O2 -> CO2 + 2H2O And a great deal of unburned CH4 is deliberately released to the atmosphere during oil drilling operations because it is “uneconomical” to capture it, or even burn it off.

Coal is the worst fuel, not only is it full of toxic impurities, it has no hydrogen, it is almost pure carbon, so every bit of coal is converted to CO2. (C + O2 -> CO2).

Since water’s melting and boiling temperatures are so close to the earth’s mean temperature, the amount of water vapor in the earth’s atmosphere is pretty much in equilibrium all the time. Adding more water isn’t going to alter the concentration of water vapor in the atmosphere, so its greenhouse contribution, although much greater than carbon dioxide’s, remains about the same. CO2, on the other hand, remains a gas at normal earth temperatures, it cannot be removed by freezing or condensation, so even the modest addition to its concentration in the atmosphere yields directly to more greenhouse effect. Since we started measuring the CO2 concentration in the atmosphere, in the 1960s (look up the Keeling Curve), its concentration has almost doubled. However, as the earth warms up, more and more of earth’s water will become vapor, raising the equilibrium point to favor higher vapor concentration, adding to the greenhouse contribution, thereby magnifying the contribution of CO2.

Its important to understand how all this works, because AGW denialists love to point out “Water vapor is a more potent greenhouse gas than CO2, and there’s a lot more of it, so rising carbon dioxide levels cannot possibly cause any global warming.”

The very fact that they know this tells us they understand the mechanism perfectly well, they just don’t care about what its results are. Their ultimate goal is to sell as much fossil fuel as possible. In other words, they are deliberately and maliciously lying. You do not courteously debate people like that. You expose them for the criminals they are..