Global Clear-Sky Aerosol Speciated Direct Radiative Effects over 40 Years (1980–2019)

Marios-Bruno Korras-Carraca,Nikolaos Hatzianastassiou,Christos Matsoukas,Antonis Gkikas

doi:10.3390/atmos12101254

Marios-Bruno Korras-Carraca, Nikolaos Hatzianastassiou + Show 2 more

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https://doi.org/10.3390/atmos12101254

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Abstract

We assess the 40-year climatological clear-sky global direct radiative effect (DRE) of five main aerosol types using the MERRA-2 reanalysis and a spectral radiative transfer model (FORTH). The study takes advantage of aerosol-speciated, spectrally and vertically resolved optical properties over the period 1980–2019, to accurately determine the aerosol DREs, emphasizing the attribution of the total DREs to each aerosol type. The results show that aerosols radiatively cool the Earth’s surface and heat its atmosphere by 7.56 and 2.35 Wm−2, respectively, overall cooling the planet by 5.21 Wm−2, partly counterbalancing the anthropogenic greenhouse global warming during 1980–2019. These DRE values differ significantly in terms of magnitude, and even sign, among the aerosol types (sulfate and black carbon aerosols cool and heat the planet by 1.88 and 0.19 Wm−2, respectively), the hemispheres (larger NH than SH values), the surface cover type (larger land than ocean values) or the seasons (larger values in local spring and summer), while considerable inter-decadal changes are evident. These DRE differences are even larger by up to an order of magnitude on a regional scale, highlighting the important role of the aerosol direct radiative effect for local and global climate.

Highlights

Understanding the current climate and predicting its future state is a major challenge and priority in the field of atmospheric sciences
MERRA-2 successfully reproduces the advection of carbonaceous aerosols originating from wildfires in the central and southern African source areas westward, to the subtropical South Atlantic Ocean and the Gulf of Guinea, reaching up the Ascension Island, as documented in literature based on satellite observations [79]
High aerosol loads are evident over the northern Indian Ocean (Arabian Sea and Bay of Bengal), due to both desert dust and carbonaceous particles transported from the adjacent regions of the Arabian Peninsula, the Indian sub-continent and South-East Asia, as well as over the western Pacific associated with outflow of dust particles originating from Asian deserts [77,78]

Summary

Introduction

Understanding the current climate and predicting its future state is a major challenge and priority in the field of atmospheric sciences. Opposite to the mostly long-lived and spatially homogeneous greenhouse gases and stratospheric aerosols, the suspended tropospheric particles, emitted either by natural or anthropogenic sources [3], have highly variable spatiotemporal distributions in their physical, chemical, optical and radiative properties [4]. This is attributed to the heterogeneity of the production (primary and secondary emissions), transport and removal (sedimentation, diffusion, turbulence and below- and in-cloud scavenging) mechanisms of tropospheric aerosols. The estimates of global and annual mean radiative forcing due to aerosol–radiation interaction still include considerable uncertainties [6]

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