Unforced Variations: Aug 2026 – RealClimate

https://www.realclimate.org/index.php/archives/2026/07/unforced-variations-july-2026/#comment-850169 “B: Changes its mind when the science at the bottom changes” Let us make a case study over this claim.. Inamdar, Ramanathan 1998: In summary, lapse rate changes for the annual cycle are not a valid analog for longer timescale climate changes. However, for reasons given below, the discrepancy in lapse rate changes between observations and GCMs do not alter our conclusion on the role of water vapor feedback. The observed annual cycle warming decreases with altitude, the decadal-scale warming remains roughly constant with altitude, while the GCM warming increases with altitude. When atmospheric warming is not so large as the surface warming, the enhanced emission to space is not so large (when compared with the situation when the warming is about the same at all altitudes), which in turn enhances dGa/dTs, i.e., a positive feedback. However, at the same time, in a fixed relative humidity environment, smaller atmospheric warming implies a smaller increase in absolute humidity, which suppresses some of the increase in dGa/dTs from the lapse rate feedback. Because of these two competing effects, the lapse rate has less than 10% influence on dGa/dTs. What happened here is that after publishing a number of papers using the
Read More