Precipitation and its response to forcing is an important aspect of planetary climate system. In this study, we examine the strength of precipitation in the experiments with different atmospheric masses and their response to surface warming, using three global atmospheric general circulation models and one regional cloud‐resolving model. We find that precipitation is weaker when atmospheric mass is larger for a given surface temperature. Furthermore, the increasing rate of precipitation with increasing surface temperature under a larger atmospheric mass is smaller than that under a smaller atmospheric mass. These behaviors can be understood based on atmospheric or surface energy balance. Atmospheric mass influences Rayleigh scattering, multiple scattering in the atmosphere, pressure broadening, lapse rate, and thereby precipitation strength. These results have important implications on the climate and habitability of early Earth, early Mars, and exoplanets with oceans.

The total mass of the atmosphere (or equivalently, the background surface pressure, SP) may have varied significantly over the evolutionary histories of Earth and other planets. Atmospheric mass can affect climate by modifying physical processes, including shortwave scattering, the emissivity of greenhouse gases, the atmospheric heat capacity, and surface fluxes. We apply a three-dimensional global climate model to explore the dependence of climate on SP over the range of 0.5 bar to 2.5 bar. Our simulations show an intriguing, nonmonotonic dependence of climate on SP. Over the SP range of 0.5 bar to 0.9 bar and 1.5 bar to 2.5 bar, the surface temperature increases with SP, however, over the SP range of 0.9 bar to 1.5 bar, the surface temperature decreases with SP. The negative correlation is due to a convection-circulation-cloud coupled feedback. As SP increases, the moist adiabatic lapse rate increases, leading to upper-troposphere cold anomalies in the tropics and middle latitudes that increase the mid-latitude baroclinicity and eddy activity. In association with these changes, the eddy-driven jet is strengthened and shifts equatorward, and two separate westerly jets merge into a single jet. These abrupt circulation changes result in an equatorward shift of the mid-latitude cloud belt and reduction of polar clouds, which induce strong negative cloud radiative forcing that cools the climate. Our results demonstrate that the regime transition of flow state (e.g., the merge of jets here) may induce large anomalies in clouds and radiative forcing, resulting in nonlinear climate responses.

Abstract. During the Archean Eon in 2.7 billion years ago, solar luminosity was about 75 % of the present-day level, but the surface temperature was suggested to similar to or even higher than modern. What mechanisms act to maintain the temperate climate of early Earth is not clearly known yet. Recent studies suggested that surface air pressure was different from the present level. How does varying surface air pressure influence the climate? Using an atmospheric general circulation model coupled to a slab ocean with specified oceanic heat transport, we show that decreasing (increasing) surface pressure acts to cool (warm) the surface mainly because the greenhouse effect of pressure broadening becomes weaker (stronger). The effect of halfing or doubling the surface pressure on the global-mean surface temperature is about 10 K or even larger when ice albedo feedback or water vapor feedback is strong. If the surface pressure was 0.5 bar, a combination of a CO2 partial pressure of about 0.04 bar and an oceanic heat transport of twice the present-day level or a combination of a CO2 partial pressure of about 0.10 bar and an oceanic heat transport of half the present-day level is required to maintain a climate similar to modern, under a given CH4 partial pressure of 1 mbar. Future work with fully coupled atmosphere-ocean models is required to explore the strength of oceanic heat transport and with cloud resolving models to examine the strength of cloud radiative effect under different surface air pressures.