Water vapor is the gaseous form of hydrogen hydroxide or H20 and is the largest “greenhouse gas.” Its spectral absorption is wider than that of carbon dioxide or CO2 meaning its absorption of photons from the Sun, as radiated by the Earth’s surface at night, across a wider EMR spectrum cause a higher rise in molecular vibrational momentum equating to higher thermal rise than CO2. Furthermore the H2O content in the lower atmosphere varies from 10,000 PPM or 1% to 40,000 PPM or 4% whereas CO2 is ≈ 400 PPM or 0.040% of the atmosphere. That is almost 2 orders of magnitude difference. This suggests that H2O has a much greater effect as a “greenhouse gas” than CO2. Water vapor is responsible for >95% of any “greenhouse effect.”
Whereas it is possible that CO2 and other non-condensable greenhouse gases like methane, CH4, nitrous oxide, N2O and ozone, O3 can create minute increases in thermal absorption and therefore could increase the amount of H2O in the atmosphere in a positive feedback cycle leading to warming and an increase in evaporation of sea water, the trace amounts of these gases would lead to virtually immeasurable temperature and water vapor increases.
However adding more water vapor to the atmosphere would also produce a negative feedback effect. This could happen as more water vapor leads to more cloud formation. Clouds reflect sunlight and reduce the amount of energy that reaches the Earth’s surface to warm it. If the amount of solar warming decreases, then the temperature of the Earth would decrease. In that case, the effect of adding more water vapor would be cooling rather than warming. But cloud cover does mean more condensed water in the atmosphere, making for a stronger greenhouse effect than non-condensed water vapor alone – it is warmer on a cloudy winter day than on a clear one. Thus the possible positive and negative feedbacks associated with increased water vapor and cloud formation will cancel one another out and complicate the ability to model these feedback cycles using computer simulation and mathematical modeling.
Dr. Fred Goldberg discusses these basic facts concerning water vapor and CO2 and their properties. He discusses the residence time in the atmosphere of human emissions, and why it has no measurable effect on the climate.