Reversal of Precipitation Trend and Large-Scale Atmospheric Temperature Inversion in Hothouse Climates

Throughout Earth's history and its potential future, surface temperatures (T_s​) have fluctuated across a far broader range than those of the present-day climate. However, the characteristics of extremely cold or warm climates remain less explored compared to modern climates. This study investigates the hydrological trends and atmospheric stratification in hothouse climates (T_s>330 K). Our results show that in climate models, precipitation decreases as surface temperature rises in hothouse climates, in contrast to the behavior observed in modern climates. This reversal trend results from the upper limit of outgoing longwave radiation and the continuously increasing shortwave absorption by H₂O and aligns with a pronounced increase in atmospheric stratification. One remarkable feature of such a highly stable atmosphere is the occurrence of a large-scale “atmospheric temperature inversion”, where the upper atmosphere is warmer than the lower’s. Although this inversion has been noted in previous studies, its formation mechanisms have remained unclear. Our work demonstrates that while radiative heating in the lower troposphere is necessary, it is not independently sufficient to form this atmospheric inversion. Instead, large-scale subsidence-induced dynamic heating plays an essential role in forming this inversion. Hothouse climates, as characterized by these findings, are feeble worlds rather than vibrant worlds.