Quantifying the range of the dust direct radiative effect due to source mineralogy uncertainty

Longlei Li,Martina Klose,David Paynter,Olga Kalashnikova,Paul Ginoux,Yves Balkanski,Ron L Miller,Vincenzo Obiso,Maria Gonçalves Ageitos,Robert O Green,Carlos Pérez García-Pando,Douglas S Hamilton,Jasper F Kok,Natalie M Mahowald,David R Thompson

doi:10.5194/acp-21-3973-2021

Abstract

Abstract. The large uncertainty in the mineral dust direct radiative effect (DRE) hinders projections of future climate change due to anthropogenic activity. Resolving modeled dust mineral speciation allows for spatially and temporally varying refractive indices consistent with dust aerosol composition. Here, for the first time, we quantify the range in dust DRE at the top of the atmosphere (TOA) due to current uncertainties in the surface soil mineralogical content using a dust mineral-resolving climate model. We propagate observed uncertainties in soil mineral abundances from two soil mineralogy atlases along with the optical properties of each mineral into the DRE and compare the resultant range with other sources of uncertainty across six climate models. The shortwave DRE responds region-specifically to the dust burden depending on the mineral speciation and underlying shortwave surface albedo: positively when the regionally averaged annual surface albedo is larger than 0.28 and negatively otherwise. Among all minerals examined, the shortwave TOA DRE and single scattering albedo at the 0.44–0.63 µm band are most sensitive to the fractional contribution of iron oxides to the total dust composition. The global net (shortwave plus longwave) TOA DRE is estimated to be within −0.23 to +0.35 W m−2. Approximately 97 % of this range relates to uncertainty in the soil abundance of iron oxides. Representing iron oxide with solely hematite optical properties leads to an overestimation of shortwave DRE by +0.10 W m−2 at the TOA, as goethite is not as absorbing as hematite in the shortwave spectrum range. Our study highlights the importance of iron oxides to the shortwave DRE: they have a disproportionally large impact on climate considering their small atmospheric mineral mass fractional burden (∼2 %). An improved description of iron oxides, such as those planned in the Earth Surface Mineral Dust Source Investigation (EMIT), is thus essential for more accurate estimates of the dust DRE.

Highlights

“Uncertainty due to dust minerals, burden, and imaginary complex refractive index”) will show that the shortwave direct radiative effect (DRE) is insensitive to minerals other than iron oxides and that the longwave DRE is insensitive to all minerals we considered here
Similar results are obtained in Community Atmosphere Model of version 4 (CAM4), because it is binned with similar diameter boundaries to CAM5
Burdens, and imaginary refractive index of minerals. This range is even narrower than the uncertainty induced by all parameters that we have considered in the perturbation analysis using CAM5 and both soil atlases, implying that the effect of inter-model differences is smaller than the uncertainty revealed by CAM5, even though the a posteriori statistical DRE calculation for the ModelE2 and GFDL models introduces uncertainties

Summary

Introduction

Mineral dust emitted from erodible land surfaces has myriad impacts on the Earth system and human society by perturbing the radiation budget (Tegen and Fung, 1994; Sokolik and Toon, 1996), interacting with cloud processes (Rosenfeld et al, 2001; DeMott et al, 2003; Mahowald and Kiehl, 2003; Atkinson et al, 2013), affecting ocean and land biogeochemical cycles (Swap et al, 1992; Jickells et al, 2005; Mahowald et al, 2017), causing respiratory and cardiovascular disease (Meng and Lu, 2007), contributing to other ailments like meningitis (Pérez García-Pando et al, 2014), and modifying atmospheric chemistry (Dentener et al, 1996; Martin et al, 2003). Mineral dust is estimated to warm the atmosphere and cool the Earth’s surface in the shortwave spectral range and induces opposite effects in the longwave spectral range (Sokolik and Toon, 1996; Kok et al, 2017). A recent review which synthesized data on dust abundance, optical properties, and size distribution estimated that at the top of the atmosphere (TOA) the shortwave, longwave, and net direct radiative effects (DREs) of dust range between [−0.81, −0.15], [0.17, 0.48], and [−0.48, +0.20] W m−2, respectively (Kok et al, 2017) This degree of uncertainty in the net DRE of dust constitutes an important gap in our understanding of the role it plays in climate

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Results

Conclusion