|Total precipitable water is an important climate parameter as it is a measure of the total amount of water vapor in the atmosphere, which is the most important greenhouse gas. |
Water vapor increases with global warming and in the climate models it amplifies the direct small warming caused by anthropogenic greenhouse gas emissions.
The greenhouse effect is much more sensitive to water vapor in the upper atmosphere than near the surface.
As seen in the graph above, this article shows that declining humidity in the upper atmosphere fully offsets the greenhouse effect of increasing humidity in the lower atmosphere.
Eliminating the water vapor feedbacks from climate models would reduce the multi-model mean equilibrium climate sensitivity from 3.2 °C to 1.7°C and would reduce the social cost of carbon dioxide calculated by the FUND economic model, with two updates, from 2018US$‑1.79/tCO2 to US$-7.14/tCO2at 3% discount rate.
The negative signs indicate that climate change is beneficial.
Note that there are other serious problems with the climate models that exaggerate climate sensitivity. The climate models fail to consider the urban heat island effect (UHIE), which contaminates the surface temperature record, and natural climate change from ocean oscillations and solar activity, which are falsely attributed to greenhouse gas warming.