The role of baroclinic activity in controlling Earth’s albedo in the present and future climates

Abstract

Clouds are one of the most influential components of Earth’s climate system. Specifically, the midlatitude clouds play a vital role in shaping Earth’s albedo. This study investigates the connection between baroclinic activity, which dominates the midlatitude climate, and cloud-albedo and how it relates to Earth’s existing hemispheric albedo symmetry. We show that baroclinic activity and cloud-albedo are highly correlated. By using Lagrangian tracking of cyclones and anticyclones and analyzing their individual cloud properties at different vertical levels, we explain why their cloud-albedo increases monotonically with intensity. We find that while for anticyclones, the relation between strength and cloudiness is mostly linear, for cyclones, in which clouds are more prevalent, the relation saturates with strength. Using the cloud-albedo strength relationships and the climatology of baroclinic activity, we demonstrate that the observed hemispheric difference in cloud-albedo is well explained by the difference in the population of cyclones and anticyclones, which counter-balances the difference in clear-sky albedo. Finally, we discuss the robustness of the hemispheric albedo symmetry in the future climate. Seemingly, the symmetry should break, as the northern hemisphere’s storm track response differs from that of the southern hemisphere due to Arctic amplification. However, we show that the saturation of the cloud response to storm intensity implies that the increase in the skewness of the southern hemisphere storm distribution toward strong storms will decrease future cloud-albedo in the southern hemisphere. This complex response explains how albedo symmetry might persist even with the predicted asymmetric hemispheric change in baroclinicity under climate change.

Connecting Hemispheric Asymmetries of Planetary Albedo and Surface Temperature

“…This mechanism is currently thought to not sufficiently explain albedo symmetry because the clouds compensating for the clear‐sky asymmetry are mostly found at extra‐tropical latitudes (Datseris & Stevens, 2021; Diamond et al., 2022; Jönsson & Bender, 2022; Stephens et al., 2015) and the interaction of the extra‐tropics and tropics are very different in fully coupled models and likely the real world than in simulations with prescribed surface fluxes or surface temperature (e.g., Hawcroft et al., 2017; Kay et al., 2016; Kim et al., 2022). Several other papers proposed “ingredients” for a potential theory of albedo symmetry without spelling out actual mechanisms of “interhemispheric communication”: the marine cloud fraction and cloud phase partitioning (Bender et al., 2017), the subtropical and midlatitude clouds (Jönsson & Bender, 2022), area‐normalized cloudiness over oceans (Datseris & Stevens, 2021) set by storminess and the efficiency of cyclones to generate clouds (Hadas et al., 2023; Shaw et al., 2022), and the aerosol clear‐sky forcing (Diamond et al., 2022).…”

“…• Climate models persistently do not simulate the observed planetary albedo symmetry • However, they do agree in a reduction of Northern minus Southern hemispheric reflectance under CO 2 forcing • Modeled bias and forced change of albedo asymmetry, as well as observed deviations from symmetry might be governed by surface temperature Bender, 2022), area-normalized cloudiness over oceans (Datseris & Stevens, 2021) set by storminess and the efficiency of cyclones to generate clouds (Hadas et al, 2023;Shaw et al, 2022), and the aerosol clear-sky forcing (Diamond et al, 2022).…”

Clouds and Seasonality on Terrestrial Planets with Varying Rotation Rates

“…Other studies have explored how obliquity influences the climatological temperature, precipitation, and habitability (Ferreira et al 2014;Linsenmeier et al 2015;Kang 2019;Lobo & Bordoni 2020;He et al 2022;Kodama et al 2022). Furthermore, Lobo & Bordoni (2022) analyzed the relationship between extratropical storminess and longwave radiation, and Hadas et al (2023) took cloud albedo into consideration, linking Earth's large-scale circulation to planetary albedo, which indicates the importance of using a more realistic radiative scheme to study the effect of rotation rate. This work builds on the above studies, especially those by Kaspi & Showman (2015) and Komacek & Abbot (2019), by interrogating the effects of clouds on varying planetary climates with idealized GCM simulations including a seasonal cycle.…”