Water vapor and solar absorption

A model that needs a water-vapor increase the air did not produce, and that misplaces solar absorption, has not closed the energy budget.

The increase is not the feedback. Over land, specific humidity rose 0.09 g/kg per decade while relative humidity fell 0.30 points per decade. Constant relative humidity is the amplifier. The observations left it.

The ocean sets the column. Allan et al. (2022) find about 1% per decade more column water from 1988 to 2014 in the observations and in atmosphere-only runs with the observed sea surface prescribed. Coupled models, which make their own warming, run wetter. The vapor follows the ocean. It is not a separate proof that CO₂ forced it.

Dry air went the other way. Simpson et al. (PNAS, 2023): Southwest vapor pressure fell about 0.6 to 0.8 hPa in 41 years. The CMIP6 range is a rise, +0.14 to +1.04 hPa. One model member is barely negative. The rest moistened a region that dried.

Solar absorption is the other miss. Arking (Science, 1996) found models under-absorb solar energy in the atmosphere by 25–30 W/m², and named water vapor as the dominant absorber. The gas the longwave feedback depends on is the gas the shortwave code gets wrong. CERES, since 2000, puts the change in Earth’s imbalance on absorbed sunlight from a lower albedo, not on a measured rise in greenhouse trapping.

Land humidity is measured from 1973. The column back to 1850 is the 20th Century Reanalysis: surface pressure goes in, and the vapor is the model’s answer. Total solar irradiance before the satellites is a sunspot reconstruction, and it only spans about 1.8 W/m².