Title: First forcing estimates from the future CMIP6 scenarios ofanthropogenic aerosol optical properties and an associated Twomeyeffect

Abstract

We present the first forcing interpretation of the future anthropogenic aerosol scenarios of CMIP6 with the simple plumes parameterisation MACv2-SP. The nine scenarios for 2015 to 2100 are based on SO₂ and NH₃ emissions for use in CMIP6 (Riahi et al., 2017; Gidden et al., in prep.). We use the emissions to scale the observationally informed anthropogenic aerosol optical properties and the associated effect on the cloud albedo of present-day (Fiedler et al., 2017; Stevens et al., 2017) into the future. The resulting scenarios in MACv2-SP are then ranked according to their strength in forcing magnitude and spatial asymmetries. Almost all scenarios show a decrease in anthropogenic aerosol by 2100 with a range of 108 % to 36 % of the anthropogenic aerosol optical depth in 2015. We estimate the spread in the radiative forcing associated with the scenarios in the mid-2090s by performing ensembles of simulations with the atmosphere-only configuration of MPI-ESM1.2. MACv2-SP herein translates the CMIP6 emission scenarios for inducing aerosol forcing. With the implementation in our model, we obtain forcing estimates for both the shortwave instantaneous (RF) and effective radiative forcing (ERF) relative to 1850. Here, ERF accounts for rapid atmospheric adjustments and natural variability internal to the model.more » The spread for the mid-2090s is −0.20 to −0.57 Wm^−2 (−0.15 to −0.54 Wm^−2) for RF (ERF) of anthropogenic aerosol, associated with uncertainty in the emission pathway alone, i.e., the mid-2090s forcing ranges from 33–95% (30–108%) of the mid-2000s RF (ERF). We find a larger ERF spread of −0.15 to −0.92 Wm^−2, when we additionally consider uncertainty in the magnitude of the Twomey effect. The year-to-year standard deviations around 0.3 Wm^−2 associated with natural variability highlights the necessity for averaging over sufficiently long time periods for estimating ERF, in contrast to RF that is typically well constrained after simulating just one year. The scenario interpretation of MACv2-SP will be used within the framework of CMIP6 and other cutting-edge scientific endeavours.« less

Authors:

Fiedler, Stephanie ^[1]; Stevens, Bjorn  ^[1];

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Gidden, Matthew  ^[2];

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Smith, Steven J.  ^[3];

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Riahi, Keywan ^[2]; van Vuuren, Detlef ^[4]

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+ Show Author Affiliations

1. Max Planck Inst. for Meteorology, Hamburg (Germany)
2. International Inst. for Applied Systems Analysis, Laxenburg (Austria)
3. Pacific Northwest National Lab. (PNNL), College Park, MD (United States). Joint Global Change Research Inst.
4. Utrecht Univ. (Netherlands); PBL Netherlands Environmental Assessment Agency (Netherlands)

Publication Date:

2018-10-16

Research Org.:

Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1557143

Report Number(s):

PNNL-SA-139734
Journal ID: ISSN 1991-962X

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Geoscientific Model Development Discussions (Online)

Additional Journal Information:

Journal Name: Geoscientific Model Development Discussions (Online); Journal Volume: 12; Journal Issue: 3; Journal ID: ISSN 1991-962X

Publisher:

European Geosciences Union

Country of Publication:

United States

Language:

English

Subject:

60 APPLIED LIFE SCIENCES