Relative importance of carbon dioxide and water in the greenhouse effect: Does the tail wag the dog?
19 hours ago Charles Rotter
In his paper, “Relative Importance of Carbon Dioxide and Water in the Greenhouse Effect: Does the Tail Wag the Dog?”, Demetris Koutsoyiannis explores the greenhouse effect’s primary drivers, positing that water vapor and clouds vastly overshadow carbon dioxide (CO₂) in terms of their contribution. Using a radiative transfer model (MODTRAN), Koutsoyiannis analyzes downwelling and outgoing longwave radiation and derives macroscopic relationships that express greenhouse gas effects quantitatively. His calculations suggest that water vapor and clouds contribute between 87% to 95% of the greenhouse effect, while CO₂’s impact is only around 4% to 5%. The findings also indicate that recent increases in atmospheric CO₂, from 300 to 420 ppm, contribute negligibly—an effect quantified at just 0.5% for both downwelling and outgoing radiation.
Abstract
Using a detailed atmospheric radiative transfer model, we derive macroscopic relationships of downwelling and outgoing longwave radiation which enable determining the partial derivatives thereof with respect to the explanatory variables that represent the greenhouse gases. We validate these macroscopic relationships using empirical formulae based on downwelling radiation data, commonly used in hydrology, and satellite data for the outgoing radiation. We use the relationships and their partial derivatives to infer the relative importance of carbon dioxide and water vapour in the greenhouse effect.
The results show that the contribution of the former is 4% – 5%, while water and clouds dominate with a contribution of 87% – 95%. The minor effect of carbon dioxide is confirmed by the small, non-discernible effect of the recent escalation of atmospheric CO₂ concentration from 300 to 420 ppm. This effect is quantified at 0.5% for both downwelling and outgoing radiation.
https://wattsupwiththat.com/2024/11/07/relative-importance-of-carbon-dioxide-and-water-in-the-greenhouse-effect-does-the-tail-wag-the-dog/
