Recent progress toward reducing the uncertainty in tropical low cloud feedback and climate sensitivity: a review

Abstract

Equilibrium climate sensitivity (ECS) to doubling of atmospheric CO 2 concentration is a key index for understanding the Earth's climate history and prediction of future climate changes. Tropical low cloud feedback, the predominant factor for uncertainty in modeled ECS, diverges both in sign and magnitude among climate models. Despite its importance, the uncertainty in ECS and low cloud feedback remains a challenge. Recently, researches based on observations and climate models have demonstrated a possibility that the tropical low cloud feedback in a perturbed climate can be constrained by the observed relationship between cloud, sea surface temperature and atmospheric dynamic and thermodynamic structures. The observational constraint on the tropical low cloud feedback suggests a higher ECS range than raw range obtained from climate model simulations. In addition, newly devised modeling frameworks that address both spreads among different model structures and parameter settings have contributed to evaluate possible ranges of the uncertainty in ECS and low cloud feedback. Further observational and modeling approaches and their combinations may help to advance toward dispelling the clouds of uncertainty.

Influence of the Subtropical High and Storm Track on Low-Cloud Fraction and Its Seasonality over the South Indian Ocean

“…As reviewed by Kamae et al (2016) and Klein et al (2017), near-surface temperature advection is recognized as an important cloud controlling factor that represents how strongly large-scale atmospheric circulation enhances upward SHF in favor of the formation of lowlevel clouds. As shown in Figs.…”

Observed Evolution of the Tropical Atmospheric Water Cycle with Sea Surface Temperature

“…In the ascending branch of the tropical hydrological cycle some observational studies concluded on weak positive correlations between both upper-tropospheric cloudiness and SST, as well as precipitation efficiency and SST (e.g., Lin et al 2006;Su et al 2008), while others observed a narrowing and strengthening of the Hadley cell with smaller average cloud cover (Su et al 2017). Low liquid water clouds in subsidence regions are another key uncertainty for climate sensitivity prediction (Bony et al 2004;Bony and Dufresne 2005;Zhai et al 2015;Kamae et al 2016;Ceppi et al 2017;Klein et al 2017). This study quantifies the cloud cover evolution with SST under both strong ascent and strong descent in instantaneous observations.…”

An energy budget framework to understand mechanisms of land–ocean warming contrast induced by increasing greenhouse gases Part I: Near-equilibrium state

“…Given that the instantaneous radiative forcing and the stratospheric adjustment are spatially uniform, the tropospheric adjustment associated with clouds is likely the key to this mechanism (Fig. 9b; Andrews et al 2012;Sherwood et al 2015;Kamae et al 2015). The horizontal distribution of all-sky and cloud-sky ERFs and the corresponding change in cloud cover (not mediated by the surface temperature change) are illustrated in Fig.…”

“…This happens within several days after the initial perturbation but remains as long as the radiative forcing exists (Dong et al 2009;Doutriaux-Boucher et al 2009). At longer time scales, land clouds may decrease with the drying of land associated with the global-mean SAT increase (Fasullo 2010;J08;Joshi et al 2013;Kamae et al 2016), thus enhancing land warming by reducing shortwave reflection.…”