scholarly journals MACv2-SP: a parameterization of anthropogenic aerosol optical properties and an associated Twomey effect for use in CMIP6

2017 ◽  
Vol 10 (1) ◽  
pp. 433-452 ◽  
Author(s):  
Bjorn Stevens ◽  
Stephanie Fiedler ◽  
Stefan Kinne ◽  
Karsten Peters ◽  
Sebastian Rast ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Industrial Emissions ◽  
Max Planck ◽  
Aerosol Optical Properties ◽  
Anthropogenic Aerosol ◽  
Aerosol Radiative Forcing ◽  
Clear Sky ◽  
Aerosol Forcing ◽  
Aerosol Radiative

Abstract. A simple plume implementation of the second version (v2) of the Max Planck Institute Aerosol Climatology, MACv2-SP, is described. MACv2-SP provides a prescription of anthropogenic aerosol optical properties and an associated Twomey effect. It was created to provide a harmonized description of post-1850 anthropogenic aerosol radiative forcing for climate modeling studies. MACv2-SP has been designed to be easy to implement, change and use, and thereby enable studies exploring the climatic effects of different patterns of aerosol radiative forcing, including a Twomey effect. MACv2-SP is formulated in terms of nine spatial plumes associated with different major anthropogenic source regions. The shape of the plumes is fit to the Max Planck Institute Aerosol Climatology, version 2, whose present-day (2005) distribution is anchored by surface-based observations. Two types of plumes are considered: one predominantly associated with biomass burning, the other with industrial emissions. These differ in the prescription of their annual cycle and in their optical properties, thereby implicitly accounting for different contributions of absorbing aerosol to the different plumes. A Twomey effect for each plume is prescribed as a change in the host model's background cloud-droplet population density using relationships derived from satellite data. Year-to-year variations in the amplitude of the plumes over the historical period (1850–2016) are derived by scaling the plumes with associated national emission sources of SO2 and NH3. Experiments using MACv2-SP are performed with the Max Planck Institute Earth System Model. The globally and annually averaged instantaneous and effective aerosol radiative forcings are estimated to be −0.6 and −0.5 W m−2, respectively. Forcing from aerosol–cloud interactions (the Twomey effect) offsets the reduction of clear-sky forcing by clouds, so that the net effect of clouds on the aerosol forcing is small; hence, the clear-sky forcing, which is more readily measurable, provides a good estimate of the total aerosol forcing.

scholarly journals Simple Plumes: A parameterization of anthropogenic aerosol optical properties and an associated Twomey effect for climate studies

2016 ◽  
Author(s):  
Bjorn Stevens ◽  
Stephanie Fiedler ◽  
Stefan Kinne ◽  
Karsten Peters ◽  
Sebastian Rast ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cloud Droplet ◽  
Anthropogenic Source ◽  
Climate Modelling ◽  
Industrial Emissions ◽  
Max Planck ◽  
Aerosol Optical Properties ◽  
Climatic Effects ◽  
Anthropogenic Aerosol ◽  
Aerosol Forcing

Abstract. A simple plume implementation of the second version (v2) of the Max Planck Institute Aerosol Climatology, MACv2-SP, is described. MACv2-SP provides a prescription of anthropogenic aerosol optical properties and an associated Twomey effect for the harmonized use in climate modelling studies. It has been designed to be easy to implement, change and use, and thereby enable studies exploring the climatic effects of different plausible aerosol distributions and their impact on clouds. MACv2-SP is formulated in terms of nine spatial plumes associated with different major anthropogenic source regions. The shape of the plumes is fit to the Max Planck Institute Aerosol Climatology, version 2, which is based on present day (2005) observations. Decadal variations in the amplitude of the plumes over the historical (post 1850) period is derived by scaling the plumes with associated national emission sources of SO2 and NH3. Two types of plumes are considered: one predominantly associated with biomass burning the other with industrial emissions. The two types of plumes differ in the prescription of their annual cycle and in their optical properties, thereby implicitly accounting for different contributions of absorbing aerosol to the different plumes. A Twomey effect for each plume is prescribed as a change in the host model's background cloud droplet population density using relationships derived from satellite data. Experiments using the simple plume model are performed with the Max Planck Institute Earth System Model. The instantaneous and effective aerosol radiative forcings is estimated to be −0.6 W m−2 and −0.7 W m−2 respectively. Forcing from aerosol-cloud interactions (the Twomey effect) offsets the reduction of clear-sky forcing from clouds, so that the net effect of clouds on the aerosol forcing is small.

scholarly journals Influence of future air pollution mitigation strategies on total aerosol radiative forcing

2008 ◽  
Vol 8 (21) ◽  
pp. 6405-6437 ◽  
Author(s):  
S. Kloster ◽  
F. Dentener ◽  
J. Feichter ◽  
F. Raes ◽  
J. van Aardenne ◽  
...  
Keyword(s):  
Air Pollution ◽  
Radiative Forcing ◽  
Mitigation Strategies ◽  
Radiation Budget ◽  
Anthropogenic Aerosol ◽  
Aerosol Radiative Forcing ◽  
Pollution Mitigation ◽  
Aerosol Forcing ◽  
Future Air Pollution ◽  
Aerosol Radiative

Abstract. We apply different aerosol and aerosol precursor emission scenarios reflecting possible future control strategies for air pollution in the ECHAM5-HAM model, and simulate the resulting effect on the Earth's radiation budget. We use two opposing future mitigation strategies for the year 2030: one in which emission reduction legislation decided in countries throughout the world are effectively implemented (current legislation; CLE 2030) and one in which all technical options for emission reductions are being implemented independent of their cost (maximum feasible reduction; MFR 2030). We consider the direct, semi-direct and indirect radiative effects of aerosols. The total anthropogenic aerosol radiative forcing defined as the difference in the top-of-the-atmosphere radiation between 2000 and pre-industrial times amounts to −2.00 W/m2. In the future this negative global annual mean aerosol radiative forcing will only slightly change (+0.02 W/m2) under the "current legislation" scenario. Regionally, the effects are much larger: e.g. over Eastern Europe radiative forcing would increase by +1.50 W/m2 because of successful aerosol reduction policies, whereas over South Asia it would decrease by −1.10 W/m2 because of further growth of emissions. A "maximum feasible reduction" of aerosols and their precursors would lead to an increase of the global annual mean aerosol radiative forcing by +1.13 W/m2. Hence, in the latter case, the present day negative anthropogenic aerosol forcing could be more than halved by 2030 because of aerosol reduction policies and climate change thereafter will be to a larger extent be controlled by greenhouse gas emissions. We combined these two opposing future mitigation strategies for a number of experiments focusing on different sectors and regions. In addition, we performed sensitivity studies to estimate the importance of future changes in oxidant concentrations and the importance of the aerosol microphysical coupling within the range of expected future changes. For changes in oxidant concentrations caused by future air pollution mitigation, we do not find a significant effect for the global annual mean radiative aerosol forcing. In the extreme case of only abating SO2 or carbonaceous emissions to a maximum feasible extent, we find deviations from additivity for the radiative forcing over anthropogenic source regions up to 10% compared to an experiment abating both at the same time.

scholarly journals Reply to “Comment on ‘Rethinking the Lower Bound on Aerosol Radiative Forcing’”

2017 ◽  
Vol 30 (16) ◽  
pp. 6585-6589 ◽  
Author(s):  
Bjorn Stevens ◽  
Stephanie Fiedler
Keyword(s):  
Twentieth Century ◽  
Lower Bound ◽  
Radiative Forcing ◽  
Climate Models ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Aerosol Radiative Forcing ◽  
Clear Sky ◽  
The North ◽  
Aerosol Forcing

Kretzschmar et al., in a comment in 2017, use the spread in the output of aerosol–climate models to argue that the models refute the hypothesis (presented in a paper by Stevens in 2015) that for the mid-twentieth-century warming to be consistent with observations, then the present-day aerosol forcing, [Formula: see text] must be less negative than −1 W m−2. The main point of contention is the nature of the relationship between global SO2 emissions and [Formula: see text] In contrast to the concave (log-linear) relationship used by Stevens and in earlier studies, whereby [Formula: see text] becomes progressively less sensitive to SO2 emissions, some models suggest a convex relationship, which would imply a less negative lower bound. The model that best exemplifies this difference, and that is most clearly in conflict with the hypothesis of Stevens, does so because of an implausible aerosol response to the initial rise in anthropogenic aerosol precursor emissions in East and South Asia—already in 1975 this model’s clear-sky reflectance from anthropogenic aerosol over the North Pacific exceeds present-day estimates of the clear-sky reflectance by the total aerosol. The authors perform experiments using a new (observationally constrained) climatology of anthropogenic aerosols to further show that the effects of changing patterns of aerosol and aerosol precursor emissions during the late twentieth century have, for the same global emissions, relatively little effect on [Formula: see text] These findings suggest that the behavior Kretzschmar et al. identify as being in conflict with the lower bound in Stevens arises from an implausible relationship between SO2 emissions and [Formula: see text] and thus provides little basis for revising this lower bound.

Composition Dependence of Stratospheric Aerosol Radiative Forcing

2021 ◽  
Author(s):  
Yaowei Li ◽  
John Dykema ◽  
Frank Keutsch
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Radiative Forcing ◽  
Complex Refractive Index ◽  
Stratospheric Aerosol ◽  
Organic Component ◽  
Aerosol Optical Properties ◽  
Aerosol Radiative Forcing ◽  
Aerosol Radiative

<p>Model results suggest organic aerosol represents a significant fraction of total stratospheric aerosol radiative forcing, which in itself could represent as much as a quarter of global radiative forcing. Other model investigations suggest that the radiative influence of organic aerosols and dust must be included to obtain consistency with satellite measurements of stratospheric aerosols. <em>In situ</em> observations suggest that stratospheric aerosol composition is strongly vertically dependent and contains a significant organic component in the lower stratosphere. Laboratory studies suggest a range of possible values for the complex refractive index of organic aerosols in the stratosphere. The real part of the refractive index could vary over a range that brackets the value of the real refractive index for pure sulfuric acid/water aerosols. The imaginary part of the refractive index of the organic component is highly uncertain, suggesting aerosols that range from being purely refractive to significantly absorbing (eg, brown carbon). The mixing state of these mixed composition aerosols is also uncertain; depending on the complex refractive index of the organic component, morphological variation could have a significant influence on aerosol radiative properties. In this work we perform a sensitivity study of shortwave radiative forcing of stratospheric aerosols, examining the influence of different plausible values of complex refractive index and particle morphologies. <em>In situ</em> measurements of aerosol size and composition are used to represent the size distribution, vertical profile, and organic mass fraction for the computation of aerosol optical properties. These profiles of aerosol optical properties are used as inputs to a radiative transfer model to calculate profiles of shortwave fluxes and radiative heating rates for standard model atmospheres. The implications of the variations in aerosol optical depth and resulting radiative forcing are interpreted in terms of implications for satellite measurements of stratospheric radiative forcing. The various radiative forcing results and remote sensing implications for different scenarios of organic complex refractive index and morphology call for better understandings of the effects of chemical evolution and transport dynamics on the aerosol optical properties in the stratosphere.</p>

scholarly journals First forcing estimates from the future CMIP6 scenarios of anthropogenic aerosol optical properties and an associated Twomey effect

2019 ◽  
Vol 12 (3) ◽  
pp. 989-1007 ◽  
Author(s):  
Stephanie Fiedler ◽  
Bjorn Stevens ◽  
Matthew Gidden ◽  
Steven J. Smith ◽  
Keywan Riahi ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Natural Variability ◽  
Aerosol Optical Properties ◽  
Anthropogenic Aerosol ◽  
Emission Pathway ◽  
Aerosol Forcing ◽  
The Future ◽  
Long Time ◽  
Spatial Asymmetries

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.

scholarly journals Influence of future air pollution mitigation strategies on total aerosol radiative forcing

2008 ◽  
Vol 8 (2) ◽  
pp. 5563-5627 ◽  
Author(s):  
S. Kloster ◽  
F. Dentener ◽  
J. Feichter ◽  
F. Raes ◽  
J. van Aardenne ◽  
...  
Keyword(s):  
Air Pollution ◽  
Radiative Forcing ◽  
Mitigation Strategies ◽  
Radiation Budget ◽  
Anthropogenic Source ◽  
Anthropogenic Aerosol ◽  
Aerosol Radiative Forcing ◽  
Aerosol Forcing ◽  
The Future ◽  
Aerosol Radiative

Abstract. We apply different aerosol and aerosol precursor emission scenarios reflecting possible future control strategies for air pollution in the ECHAM5-HAM model, and simulate the resulting effect on the Earth's radiation budget. We use two opposing future mitigation strategies for the year 2030: one in which emission reduction legislation decided in countries throughout the world are effectively implemented (current legislation; CLE 2030) and one in which all technical options for emission reductions are being implemented independent of their cost (maximum feasible reduction; MFR 2030). We consider the direct, semi-direct and indirect radiative effects of aerosols. The total anthropogenic aerosol radiative forcing defined as the difference in the top-of-the-atmosphere radiation between 2000 and pre-industrial times amounts to −2.05 W/m2. In the future this negative global annual mean aerosol radiative forcing will only slightly change (+0.02 W/m2) under the "current legislation" scenario. Regionally, the effects are much larger: e.g. over Eastern Europe radiative forcing would increase by +1.50 W/m2 because of successful aerosol reduction policies, whereas over South Asia it would decrease by −1.10 W/m2 because of further growth of emissions. A "maximum feasible reduction" of aerosols and their precursors would lead to an increase of the global annual mean aerosol radiative forcing by +1.13 W/m2. Hence, in the latter case, the present day negative anthropogenic aerosol forcing cloud be more than halved by 2030 because of aerosol reduction policies and climate change thereafter will be to a larger extend be controlled by greenhouse gas emissions. We combined these two opposing future mitigation strategies for a number of experiments focusing on different sectors and regions. In addition, we performed sensitivity studies to estimate the importance of future changes in oxidant concentrations and the importance of the aerosol microphysical coupling within the range of expected future changes. For changes in oxidant concentrations in the future within a realistic range, we do not find a significant effect for the global annual mean radiative aerosol forcing. In the extreme case of only abating SO2 or carbonaceous emissions to a maximum feasible extent, we find deviations from additivity for the radiative forcing over anthropogenic source regions up to 10% compared to an experiment abating both at the same time.

scholarly journals Aerosol Characterization and Direct Radiative Forcing Assessment over the Ocean. Part I: Methodology and Sensitivity Analysis

2004 ◽  
Vol 43 (12) ◽  
pp. 1799-1817 ◽  
Author(s):  
Maria João Costa ◽  
Ana Maria Silva ◽  
Vincenzo Levizzani
Keyword(s):  
Sensitivity Analysis ◽  
Optical Properties ◽  
Radiative Forcing ◽  
High Spectral Resolution ◽  
Earth Orbit ◽  
Aerosol Optical Properties ◽  
Aerosol Model ◽  
Aerosol Radiative Forcing ◽  
The Impact ◽  
Aerosol Radiative

Abstract A method based on the synergistic use of low earth orbit (LEO) and geostationary earth orbit (GEO) satellite data for aerosol-type characterization, as well as aerosol optical thickness (AOT) retrieval and monitoring over the ocean, is presented. These properties are used for the estimation of the direct shortwave aerosol radiative forcing at the top of the atmosphere. The synergy serves the purpose of monitoring aerosol events at the GEO time and space scales while maintaining the accuracy level achieved with LEO instruments. Aerosol optical properties representative of the atmospheric conditions are obtained from the inversion of high-spectral-resolution measurements from the Global Ozone Monitoring Experiment (GOME). The aerosol optical properties are input for radiative transfer calculations for the retrieval of the AOT from GEO visible broadband measurements, avoiding the use of fixed aerosol models available in the literature. The retrieved effective aerosol optical properties represent an essential component for the aerosol radiative forcing assessment. A sensitivity analysis is also presented to quantify the effects that changes on the aerosol model may have on modeled results of spectral reflectance, AOT, and direct shortwave aerosol radiative forcing at the top of the atmosphere. The impact on modeled values of the physical assumptions on surface reflectance and vertical profiles of ozone and water vapor are analyzed. Results show that the aerosol model is the main factor influencing the investigated radiative variables. Results of the application of the method to several significant aerosol events, as well as their validation, are presented in a companion paper.

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