it is unimaginable that any month in the last few thousand years, maybe 100,000 years, has more PWAT in the atmosphere than August 2026. We are, as the proverb says, living in interesting times.

I'll note that water vapor, while a greenhouse gas, cycles out of the atmosphere quite quickly, making the amount present dependent on temperature, and hence the concentration of the long-lived greenhouse gases. It's a well-established feedback mechanism