Journal Article
Geoscientific Model Development, vol. 12, iss. 3, pp. 989-1007, 2019
Authors
Stephanie Fiedler, Bjorn Stevens, Matthew Gidden, Steven J. Smith, Keywan Riahi, DETLEF VAN VUUREN
Abstract
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
anthropogenic aerosol emissions for use in CMIP6
(Riahi et al., 2017; Gidden et al., 2018). 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 for anthropogenic aerosol. All scenarios, except SSP3-70
and SSP4-60, show a decrease in anthropogenic aerosol by 2100 with a range
from 108 % to 36 % of the anthropogenic aerosol optical depth in 2015. We estimate
the radiative forcing of anthropogenic aerosol from high- and low-end
scenarios in the mid-2090s by performing ensembles of simulations with the
atmosphere-only configuration of MPI-ESM1.2. MACv2-SP translates the
CMIP6 emission scenarios for inducing anthropogenic aerosol forcing. With the
implementation in our model, we obtain forcing estimates for both the
shortwave instantaneous radiative forcing (RF) and the effective radiative forcing (ERF) of
anthropogenic aerosol relative to 1850. Here, ERF accounts for rapid
atmospheric adjustments and natural variability internal to the model. The
ERF of anthropogenic aerosol for the mid-2090s ranges from −0.15 W m−2
for SSP1-19 to −0.54 W m−2 for SSP3-70, i.e. the mid-2090s ERF is
30 %–108 % of the value in the mid-2000s due to differences in the emission
pathway alone. Assuming a stronger Twomey effect changes these ERFs to
−0.39 and −0.92 W m−2, respectively, which are similar to
estimates obtained from models with complex aerosol parameterisations. The
year-to-year standard deviations around 0.3 W m−2 associated with
natural variability highlight the necessity to average over sufficiently
long time periods for estimating ERF; this is in contrast to RF that is typically
well constrained after simulating just 1 year. The scenario interpretation
of MACv2-SP will be used within the framework of CMIP6 and other cutting-edge
scientific endeavours.
