Global fine-mode aerosol radiative effect, as constrained by comprehensive observations

Abstract

Abstract. Aerosols directly affect the radiative balance of the Earth through the absorption and scattering of solar radiation. Although the contributions of absorption (heating) and scattering (cooling) of sunlight have proved difficult to quantify, the consensus is that anthropogenic aerosols cool the climate, partially offsetting the warming by rising greenhouse gas concentrations. Recent estimates of global direct anthropogenic aerosol radiative forcing (i.e., global radiative forcing due to aerosol-radiation interactions) are −0.35 ± 0.5 W m −2 , and these estimates depend heavily on aerosol simulation. Here, we integrate a comprehensive suite of satellite and ground-based observations to constrain total aerosol optical depth (AOD), its fine-mode fraction, the vertical distribution of aerosols and clouds, and the collocation of clouds and overlying aerosols. We find that the direct fine-mode aerosol radiative effect is −0.46 W m −2 (−0.54 to −0.39 W m −2 ). Fine-mode aerosols include sea salt and dust aerosols, and we find that these natural aerosols result in a very large cooling (−0.44 to −0.26 W m −2 ) when constrained by observations. When the contribution of these natural aerosols is subtracted from the fine-mode radiative effect, the net becomes −0.11 (−0.28 to +0.05) W m −2 . This net arises from total (natural + anthropogenic) carbonaceous, sulfate and nitrate aerosols, which suggests that global direct anthropogenic aerosol radiative forcing is less negative than −0.35 W m −2 .

The Semidirect Effect of Combined Dust and Sea Salt Aerosols in a Multimodel Analysis

“…F SFC ranges from −2.48 to −2.07 W/m 2 , and F ATM ranges from 0.85 to 1.16 W/m 2 in HadGEM2‐ES and INCA, respectively. F SFC from Chung et al (; −3.3 W/m 2 ) is about 45% larger than these model estimates. F ATM from Chung et al (; 1.12 W/m 2 ) is similar to that simulated by INCA.…”

“…The Africa region is designated by the red box in (a). This forcing is estimated by Chung et al () using the MACR radiation model and is subsequently inserted into our climate models to estimate the cloud rapid adjustment. Unit in (a) and (b) is watt per square meter; unit in (c) and (d) is kelvin per day.…”

“…We use semiempirical aerosol DRE data from Chung et al (2016), which is based on the approach of Chung et al (2005) and Lee and Chung (2013). Indirect aerosol (cloud microphysical) effects are not included.…”

“…In an attempt to circumvent some of these uncertainties, we use the top‐down approach, involving prescribing aerosol optical properties based on a combination of observations and models. Specifically, we prescribe a monthly varying climatology of semiempirical dust and sea salt direct radiative effects (DREs) (Chung et al, ) into multiple atmospheric general circulation models to quantify the SDE. Our simulations only account for aerosol direct effects and SDEs and do not include cloud microphysical (indirect) effects.…”

CALIPSO lidar level 3 aerosol profile product: version 3 algorithm design

“…Vertical extinction profiles have helped to interpret seasonal surface PM2.5 variability (Ma et al, 2016) and to evaluate estimates of wildfire injection heights (Sofiev et 5 al., 2013). Aerosol radiative effect investigations have also benefited from the level 3 aerosol product (Adebiyi et al, 2015;Chung et al, 2016).…”