Clouds exhibit a net cooling effect on global climate while providing positive climate feedback through thermal trapping
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Retrieved literature confirms that clouds exert a net cooling influence on the Earth's global climate system while simultaneously providing thermal trapping and longwave warming effects.
Ice clouds play a significant role in the Earth’s radiation balance due to their unique microphysical and radiative properties, which vary with formation mechanisms and regions and influence the local energy budget. In this study, six years of Ka-band Zenith Radar (KAZR) observations from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) and the Southern Great Plains (SGP) sites, combined with the Fu–Liou radiative transfer model, were used to examine the macrophysical and microphysical properties of ice clouds, their radiative effects, and contributions to the surface energy budget. The results show that the frequency of ice cloud occurrence at SACOL is 40%, significantly higher than the 27% observed at SGP. At both sites, ice cloud altitudes exhibit an increasing trend in the context of recent warming, with a more pronounced increase at SGP. Seasonal variations are evident, with spring characterized by relatively thick and widespread ice clouds, while summer is dominated by high-altitude, optically thin clouds. Ice cloud occurrence peaks at night and decreases during the day at both sites; however, cloud diurnal variations in summer are much greater at SGP than at SACOL. Radiative analysis indicates that longwave radiation-induced warming dominates ice cloud radiative forcing. Net radiative forcing at the top of the atmosphere is 6.08 W/m 2 at SACOL and 3.06 W/m 2 at SGP, contributing to atmospheric heating within and beneath cloud layers. At t
Warmer temperatures are expected to cause more intense rainfall, primarily due to the rise in atmospheric moisture at the rate of 7%/K, as indicated by the Clausius-Clapeyron (CC) equation. To evaluate this effect, studies use a statistical approach known as precipitation-temperature scaling that involves fitting an exponential regression between observations of extreme rainfall events and local temperatures, resembling how saturation-vapor pressure scales with temperature. However, the estimated sensitivities (also called scaling rates), exhibit notable deviations from the CC scaling (7%/K). These rates remain mostly negative in the tropics as the rainfall extremes exhibit a general monotonic decrease with temperature and “hook-shape” structures in most parts of tropics and mid-latitudes.Here we show that most of the variability in the observed scaling rates arises from the confounding radiative effect of clouds associated with rainfall events. Clouds substantially reduce the net radiative heating of the surface during the storms by up to 100 W/m2 in the tropics, leading to the cooling of surface temperatures by up to 8K. This cloud-induced cooling results in a covariation between precipitation and local temperature, inducing a two-way causality in the observed scaling rates. To isolate this cooling effect, we used a thermodynamically constrained surface energy balance model and force it with radiative fluxes under both "clear" and "cloudy" sky conditions. We the
Abstract Climate models exhibit major radiative biases over the Southern Ocean owing to a poor representation of mixed‐phase clouds. This study uses the remote‐sensing dataset from the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean (MARCUS) campaign to assess the ability of the Weather Research and Forecasting (WRF) model to reproduce frontal clouds off Antarctica. It focuses on the modeling of thin mid‐level supercooled liquid water layers which precipitate ice. The standard version of WRF produces almost fully glaciated clouds and cannot reproduce cloud top turbulence. Our work demonstrates the importance of adapting the ice nucleation parameterization to the pristine austral atmosphere to reproduce the supercooled liquid layers. Once simulated, droplets significantly impact the cloud radiative effect by increasing downwelling longwave fluxes and decreasing downwelling shortwave fluxes at the surface. The net radiative effect is a warming of snow and ice covered surfaces and a cooling of the ocean. Despite improvements in our simulations, the local turbulent circulation related to cloud‐top radiative cooling is not properly reproduced, advocating for the need to develop a parameterization for top‐down convection to capture the turbulence‐microphysics interplay at cloud top.
Climate models exhibit major radiative biases over the Southern Ocean owing to a poor representation of mixed-phase clouds. This study uses the remote-sensing dataset from the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean (MARCUS) campaign to assess the ability of the Weather Research and Forecasting (WRF) model to reproduce frontal clouds off Antarctica. It focuses on the modeling of thin mid-level supercooled liquid water layers which precipitate ice. The standard version of WRF produces almost fully glaciated clouds and cannot reproduce cloud top turbulence. Our work demonstrates the importance of adapting the ice nucleation parameterization to the pristine austral atmosphere to reproduce the supercooled liquid layers. Once simulated, droplets significantly impact the cloud radiative effect by increasing downwelling longwave fluxes and decreasing downwelling shortwave fluxes at the surface. The net radiative effect is a warming of snow and ice covered surfaces and a cooling of the ocean. Despite improvements in our simulations, the local circulation related to cloud-top radiative cooling is not properly reproduced, advocating for the need to develop a parameterization for top-down convection to capture the turbulence-microphysics interplay at cloud top.
Land and oceanic convection exhibit significant contrasts in intensity and entrainment, but their effects on the properties of other cloud types remain unclear. This study examines a 19-year mean of cloud properties and top-of-the-atmosphere (TOA) cloud radiative effects (CREs) by cloud type, with a focus on regional variations across convectively active tropical regions. Forty-two cloud types are classified based on effective cloud-top pressure and cloud optical depth. The analysis reveals distinct regional differences in cloud occurrence and properties, with oceanic regions dominated by convective anvils and boundary-layer clouds, which have higher liquid/ice water contents, while land regions feature higher fractions of mid-level clouds with lower liquid/ice water contents. The study further explores shortwave (SW), longwave (LW), and net CREs, decomposing the contributions of individual cloud types to total CRE differences between two regions into three components: CRE deviations within a cloud type, cloud fraction (CF) deviations, and their combined effect. Results show that CF deviations have the largest impact, enhancing LW warming and SW cooling for mid- and high-level clouds while reducing SW and net cooling for low-level clouds. Although the effects of CRE deviations are smaller than those of CF deviations for individual cloud types, its collective contribution to total regional CRE differences, particularly for net CRE, is more comparable, because the former exhibi
Satellite measurements from the Earth Radiation Budget Experiment (ERBE) are providing new insights into the earth radiation balance. The ERBE results indicate that clouds have more of a cooling effect than a greenhouse warming effect on the earth-atmosphere system. The largest net-radiation cooling appears over the midlatitude oceans in the summer hemisphere where maximum sunlight and maximum cloud cover occur. The ERBE data also have shown that many areas of the earth exhibit significant diurnal variations in both longwave and shortwave radiation. In order to assess future global climatic changes, a follow-on experiment to ERBE, called Clouds and Earth's Radiant Energy System (CERES), has been selected to fly on the Earth Observing System in the the 1990's.
Calculations of radiative flux profiles require measurements of thermodynamic and cloud properties (temperature, humidity, liquid and ice water content). Instruments capable of making these measurements have only recently become available. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program operates a comprehensive set of atmospheric remote sensing instruments at sites around the world, including three in the tropical western Pacific region. We have processed several months of ARM observations from two of these sites, Manus and Nauru, to calculate time series of vertical cloud property profiles and associated radiative fluxes and heating rates. Maxima in cloud occurrence are found in the boundary layer and the upper troposphere at both sites. Manus, which was much more convectively active than Nauru during the study period, also exhibits a midlevel cloud feature near the melting level. The two sites exhibit very different diurnal cycles. Manus experiences an afternoon maximum in high clouds while Nauru experiences a weak afternoon minimum. Nauru experiences a strong afternoon maximum in boundary layer clouds. Calculated fluxes at the surface and the top of the atmosphere are found to be in reasonable agreement with measurements. Below 15 km, radiative processes lead to cooling in the average profile, with local maxima near the surface and approximately 8 km. On average, high and midlevel clouds have a net warming effect though not enough to offset th
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