Global and Arctic effective radiative forcing of anthropogenic gases and aerosols in MRI-ESM2.0

Naga Oshima,Tsuyoshi Koshiro,Kohei Yoshida,Taichu Y Tanaka,Hideaki Kawai,Makoto Deushi,Seiji Yukimoto

doi:10.1186/s40645-020-00348-w

Naga Oshima, Tsuyoshi Koshiro + Show 5 more

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https://doi.org/10.1186/s40645-020-00348-w

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Abstract

The effective radiative forcing (ERF) of anthropogenic gases and aerosols under present-day conditions relative to preindustrial conditions is estimated using the Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0) as part of the Radiative Forcing Model Intercomparison Project (RFMIP) and Aerosol and Chemistry Model Intercomparison Project (AerChemMIP), endorsed by the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The global mean total anthropogenic net ERF estimate at the top of the atmosphere is 1.96 W m−2 and is composed primarily of positive forcings due to carbon dioxide (1.85 W m−2), methane (0.71 W m−2), and halocarbons (0.30 W m−2) and negative forcing due to the total aerosols (− 1.22 W m−2). The total aerosol ERF consists of 23% from aerosol-radiation interactions (− 0.32 W m−2), 71% from aerosol-cloud interactions (− 0.98 W m−2), and slightly from surface albedo changes caused by aerosols (0.08 W m−2). The ERFs due to aerosol-radiation interactions consist of opposing contributions from light-absorbing black carbon (BC) (0.25 W m−2) and from light-scattering sulfate (− 0.48 W m−2) and organic aerosols (− 0.07 W m−2) and are pronounced over emission source regions. The ERFs due to aerosol-cloud interactions (ERFaci) are prominent over the source and downwind regions, caused by increases in the number concentrations of cloud condensation nuclei and cloud droplets in low-level clouds. Concurrently, increases in the number concentration of ice crystals in high-level clouds (temperatures < –38 °C), primarily induced by anthropogenic BC aerosols, particularly over tropical convective regions, cause both substantial negative shortwave and positive longwave ERFaci values in MRI-ESM2.0. These distinct forcings largely cancel each other; however, significant longwave radiative heating of the atmosphere caused by high-level ice clouds suggests the importance of further studies on the interactions of aerosols with ice clouds. Total anthropogenic net ERFs are almost entirely positive over the Arctic due to contributions from the surface albedo reductions caused by BC. In the Arctic, BC provides the second largest contribution to the positive ERFs after carbon dioxide, suggesting a possible important role of BC in Arctic surface warming.

Highlights

Anthropogenic gases and aerosols affect radiation balance on the Earth and cause climate change over the industrial era
The effective radiative forcing (ERF) induced by the total anthropogenic components is estimated to be 1.96 W m−2, composed of a positive ERF due to the well-mixed greenhouse gases (3.02 W m−2), negative ERFs due to the Near-term climate forcers (NTCFs) (− 1.08 W m−2), which are mostly due to aerosols (− 1.22 W m−2), and slightly negative ERFs due to land-use changes (− 0.19 W m−2)
In comparison to the best ERF estimates in Intergovernmental Panel on Climate Change (IPCC) AR5, the ERF estimates by Meteorological Research Institute (MRI)-ESM2.0 in this study show lower total anthropogenic ERF by 0.33 W m−2 and more negative total aerosol ERF by 0.4 W m−2

Summary

Introduction

Anthropogenic gases and aerosols affect radiation balance on the Earth and cause climate change over the industrial era. Because BC strongly absorbs SW radiation and leads to atmospheric heating, climate responses to BC in the Earth system are complex (e.g., Jacobson 2002; Bond et al 2013; Stohl et al 2015; Kaiho et al 2016; Kaiho and Oshima 2017; Suzuki and Takemura 2019; Takemura and Suzuki 2019), and the role of BC has been recognized as being important in the Arctic (e.g., Arctic Monitoring and Assessment Programme (AMAP) 2015; Sand et al 2015; Mahmood et al 2016)

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