The Impacts of Aerosol Emissions on Historical Climate in UKESM1

As one of the main drivers for climate change, it is important to understand changes in anthropogenic aerosol emissions and evaluate the climate impact. Anthropogenic aerosols have affected global climate while exerting a much larger influence on regional climate by their short lifetime and heterogeneous spatial distribution. In this study, the effective radiative forcing (ERF), which has been accepted as a useful index for quantifying the effect of climate forcing, was evaluated to understand the effects of aerosol on regional climate over a historical period (1850–2014). Eastern United States (EUS), Western European Union (WEU), and Eastern Central China (ECC), are regions that predominantly emit anthropogenic aerosols and were analyzed using Coupled Model Intercomparison Project 6 (CMIP6) simulations implemented within the framework of the Aerosol Chemistry Model Intercomparison Project (AerChemMIP) in the UK’s Earth System Model (UKESM1). In EUS and WEU, where industrialization occurred relatively earlier, the negative ERF seems to have been recovering in recent decades based on the decreasing trend of aerosol emissions. Conversely, the radiative cooling in ECC seems to be strengthened as aerosol emission continuously increases. These aerosol ERFs have been largely attributed to atmospheric rapid adjustments, driven mainly by aerosol-cloud interactions rather than direct effects of aerosol such as scattering and absorption.

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The local and remote atmospheric impacts of Africa’s 21st century aerosol emission trajectory

10.5194/egusphere-egu21-14417 ◽

2021 ◽

Author(s):

Chris Wells ◽

Apostolos Voulgarakis

Keyword(s):

Regional Climate ◽

Emission Region ◽

Anthropogenic Aerosol ◽

Remote Locations ◽

Aerosol Emission ◽

Radiation Fluxes ◽

The World ◽

Aerosol Emissions ◽

The Impact ◽

Lower Biomass

<p>Aerosols are a major climate forcer, but their historical effect has the largest uncertainty of any forcing; their mechanisms and impacts are not well understood. Due to their short lifetime, aerosols have large impacts near their emission region, but they also have effects on the climate in remote locations. In recent years, studies have investigated the influences of regional aerosols on global and regional climate, and the mechanisms that lead to remote responses to their inhomogeneous forcing. Using the Shared Socioeconomic Pathway scenarios (SSPs), transient future experiments were performed in UKESM1, testing the effect of African emissions following the SSP3-RCP7.0 scenario as the rest of the world follows SSP1-RCP1.9, relative to a global SSP1-RCP1.9 control. SSP3 sees higher direct anthropogenic aerosol emissions, but lower biomass burning emissions, over Africa. Experiments were performed changing each of these sets of emissions, and both. A further set of experiments additionally accounted for changing future CO<sub>2</sub> concentrations, to investigate the impact of CO<sub>2</sub> on the responses to aerosol perturbations. Impacts on radiation fluxes, temperature, circulation and precipitation are investigated, both over the emission region (Africa), where microphysical effects dominate, and remotely, where dynamical influences become more relevant.&#160;</p>

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AerChemMIP: quantifying the effects of chemistry and aerosols in CMIP6

Geoscientific Model Development ◽

10.5194/gmd-10-585-2017 ◽

2017 ◽

Vol 10 (2) ◽

pp. 585-607 ◽

Cited By ~ 66

Author(s):

William J. Collins ◽

Jean-François Lamarque ◽

Michael Schulz ◽

Olivier Boucher ◽

Veronika Eyring ◽

...

Keyword(s):

Air Quality ◽

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Models ◽

Coupled Model ◽

Climate Impacts ◽

Atmospheric Composition ◽

Historical Period ◽

Model Intercomparison ◽

Intercomparison Project

Abstract. The Aerosol Chemistry Model Intercomparison Project (AerChemMIP) is endorsed by the Coupled-Model Intercomparison Project 6 (CMIP6) and is designed to quantify the climate and air quality impacts of aerosols and chemically reactive gases. These are specifically near-term climate forcers (NTCFs: methane, tropospheric ozone and aerosols, and their precursors), nitrous oxide and ozone-depleting halocarbons. The aim of AerChemMIP is to answer four scientific questions. 1. How have anthropogenic emissions contributed to global radiative forcing and affected regional climate over the historical period? 2. How might future policies (on climate, air quality and land use) affect the abundances of NTCFs and their climate impacts? 3.How do uncertainties in historical NTCF emissions affect radiative forcing estimates? 4. How important are climate feedbacks to natural NTCF emissions, atmospheric composition, and radiative effects? These questions will be addressed through targeted simulations with CMIP6 climate models that include an interactive representation of tropospheric aerosols and atmospheric chemistry. These simulations build on the CMIP6 Diagnostic, Evaluation and Characterization of Klima (DECK) experiments, the CMIP6 historical simulations, and future projections performed elsewhere in CMIP6, allowing the contributions from aerosols and/or chemistry to be quantified. Specific diagnostics are requested as part of the CMIP6 data request to highlight the chemical composition of the atmosphere, to evaluate the performance of the models, and to understand differences in behaviour between them.

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The Radiative Forcing Model Intercomparison Project (RFMIP): Experimental Protocol for CMIP6

10.5194/gmd-2016-88 ◽

2016 ◽

Cited By ~ 8

Author(s):

Robert Pincus ◽

Piers M. Forster ◽

Bjorn Stevens

Keyword(s):

Radiative Forcing ◽

Complete Characterization ◽

Atmospheric Conditions ◽

Model Intercomparison ◽

Anthropogenic Aerosol ◽

Sea Ice Concentration ◽

Tier 1 ◽

Intercomparison Project ◽

Effective Radiative Forcing

Abstract. The phrasing of the first of three questions motivating CMIP6 – "How does the Earth system respond to forcing?" – suggests that forcing is always well-known, but in fact forcing has historically been uncertain even in coordinated experiments such as CMIP. The Radiative Forcing Model Intercomparison Project endorsed by CMIP6 seeks to provide a foundation for answering the question for forcing and response through three related activities: (i) accurate characterization of the effective radiative forcing relative to a near pre-industrial baseline, and careful diagnosis of the components of this forcing; (ii) assessment of the absolute accuracy of clear-sky radiative transfer parameterizations against reference models on the global scales relevant for climate modeling; and (iii) identification of robust model responses to a tightly-specified aerosol radiative forcing from 1850 to present. Complete characterization of effective radiative forcing can be accomplished with 180 years (Tier 1) of atmosphere-only simulation using a sea-surface temperature and sea ice concentration climatology derived from the host model's pre-industrial control simulation. Assessment of parameterization error requires trivial amounts of computation but the development of small amounts of infrastructure: new, spectrally-detailed diagnostic output requested as two snapshots at present-day and preindustrial conditions, and results from the model's radiation code applied to specified atmospheric conditions. The search for robust responses to aerosol changes rely on the CMIP6 specification of anthropogenic aerosol properties; models using this specification can contribute to RFMIP with no additional simulation, while those using a full aerosol model are requested to perform at least one, and up to four, 165-year coupled ocean-atmosphere simulations at Tier 1.

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AerChemMIP: Quantifying the effects of chemistry and aerosols in CMIP6

10.5194/gmd-2016-139 ◽

2016 ◽

Cited By ~ 7

Author(s):

William J. Collins ◽

Jean-François Lamarque ◽

Michael Schulz ◽

Olivier Boucher ◽

Veronika Eyring ◽

...

Keyword(s):

Air Quality ◽

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Models ◽

Coupled Model ◽

Climate Impacts ◽

Anthropogenic Emissions ◽

Historical Period ◽

Model Intercomparison ◽

Intercomparison Project

Abstract. The Aerosol Chemistry Model Intercomparison Project (AerChemMIP) is endorsed by the Coupled-Model Intercomparison Project 6 (CMIP6) and is designed to quantify the climate and air quality impacts of aerosols and chemically-reactive gases. These are specifically near-term climate forcers (NTCFs: tropospheric ozone and aerosols, and their precursors), methane, nitrous oxide and ozone-depleting halocarbons. The aim of AerChemMIP is to answer four scientific questions: 1. How have anthropogenic emissions contributed to global radiative forcing and affected regional climate over the historical period? 2. How will future policies (on climate, air quality and land use) affect these species and their climate impacts? 3. Can the uncertainties associated with anthropogenic emissions be quantified? 4. Can climate feedbacks occurring through changes in natural emissions be quantified? These questions will be addressed through targeted simulations with CMIP6 climate models that include an interactive representation of tropospheric aerosols and atmospheric chemistry. These simulations build on the CMIP6 Diagnostic, Evaluation and Characterization of Klima (DECK) experiments, the CMIP6 historical simulations, and future projections performed elsewhere in CMIP6, allowing the contributions from aerosols and chemistry to be quantified. Specific diagnostics are requested as part of the CMIP6 data request to evaluate the performance of the models, and to understand any differences in behaviour between them.

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The Radiative Forcing Model Intercomparison Project (RFMIP): experimental protocol for CMIP6

Geoscientific Model Development ◽

10.5194/gmd-9-3447-2016 ◽

2016 ◽

Vol 9 (9) ◽

pp. 3447-3460 ◽

Cited By ~ 70

Author(s):

Robert Pincus ◽

Piers M. Forster ◽

Bjorn Stevens

Keyword(s):

Radiative Forcing ◽

Complete Characterization ◽

Atmospheric Conditions ◽

Model Intercomparison ◽

Anthropogenic Aerosol ◽

Sea Ice Concentration ◽

Tier 1 ◽

Intercomparison Project ◽

Effective Radiative Forcing

Abstract. The phrasing of the first of three questions motivating CMIP6 – “How does the Earth system respond to forcing?” – suggests that forcing is always well-known, yet the radiative forcing to which this question refers has historically been uncertain in coordinated experiments even as understanding of how best to infer radiative forcing has evolved. The Radiative Forcing Model Intercomparison Project (RFMIP) endorsed by CMIP6 seeks to provide a foundation for answering the question through three related activities: (i) accurate characterization of the effective radiative forcing relative to a near-preindustrial baseline and careful diagnosis of the components of this forcing; (ii) assessment of the absolute accuracy of clear-sky radiative transfer parameterizations against reference models on the global scales relevant for climate modeling; and (iii) identification of robust model responses to tightly specified aerosol radiative forcing from 1850 to present. Complete characterization of effective radiative forcing can be accomplished with 180 years (Tier 1) of atmosphere-only simulation using a sea-surface temperature and sea ice concentration climatology derived from the host model's preindustrial control simulation. Assessment of parameterization error requires trivial amounts of computation but the development of small amounts of infrastructure: new, spectrally detailed diagnostic output requested as two snapshots at present-day and preindustrial conditions, and results from the model's radiation code applied to specified atmospheric conditions. The search for robust responses to aerosol changes relies on the CMIP6 specification of anthropogenic aerosol properties; models using this specification can contribute to RFMIP with no additional simulation, while those using a full aerosol model are requested to perform at least one and up to four 165-year coupled ocean–atmosphere simulations at Tier 1.

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Uncertainty in aerosol radiative forcing impacts the simulated global monsoon in the 20th century

10.5194/egusphere-egu2020-16401 ◽

2020 ◽

Author(s):

Andrew Turner ◽

Jonathan Shonk ◽

Laura Wilcox ◽

Andrea Dittus ◽

Ed Hawkins

Keyword(s):

Radiative Forcing ◽

Monsoon Rainfall ◽

Strong Relationship ◽

Dynamical Response ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Global Monsoon ◽

Monsoon Area ◽

Hemispheric Temperature ◽

Aerosol Emissions

<div> <div> <div> <p>Anthropogenic aerosols are dominant drivers of historical monsoon rainfall change.&#160; However, large uncertainties in the radiative forcing associated with anthropogenic aerosol emissions, and the dynamical response to this forcing, lead to uncertainty in the simulated monsoon response.&#160; We use historical simulations in which aerosol emissions are scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to aerosol forcing uncertainty (&#8722;0.3 W m&#8722;2 to &#8722;1.6 W m&#8722;2).&#160; Hemispheric asymmetry in emissions generates a strong relationship between scaling factor and both hemispheric temperature contrast and meridional location of tropical rainfall.&#160; Increasing the&#160; scaling from 0.2 to 1.5 reduces the global monsoon area by 3% and the global monsoon intensity by 2% over 1950&#8211;2014, and changes the dominant influence on the 1950&#8211;1980 monsoon rainfall trend from greenhouse gas to aerosol.&#160;&#160; Regionally, aerosol scaling has a pronounced effect on Northern Hemisphere monsoon rainfall.</p> </div> </div> </div>

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Implication of the reduction in anthropogenic aerosols due to the COVID-19 pandemic and the future recovery scenarios for radiative forcing

10.5194/egusphere-egu21-928 ◽

2021 ◽

Author(s):

Stephanie Fiedler ◽

Klaus Wyser ◽

Rogelj Joeri ◽

Twan van Noije

Keyword(s):

Radiative Forcing ◽

Internal Variability ◽

Climate Response ◽

Emission Scenarios ◽

Radiative Effects ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Aerosol Forcing ◽

Effective Radiative Forcing ◽

Aerosol Emissions

<p>The COVID-19 pandemic has led to unprecedented reductions in socio-economic activities. Associated decreases in anthropogenic aerosol emissions are not represented in the original CMIP6 emission scenarios. Here we estimate the implications of the pandemic for the aerosol forcing in 2020 and quantify the spread in aerosol forcing associated with the differences in the post-pandemic recovery pathways. To this end, we use new emission scenarios taking the COVID-19 crisis into account and projecting different socio-economic developments until 2050 with fossil-fuel based and green pathways (Forster et al., 2020). We use the new emission data to generate input for the anthropogenic aerosol parameterization MACv2-SP for CMIP6 models. In this presentation, we first show the results for the anthropogenic aerosol optical depth and associated effects on clouds from the new MACv2-SP data for 2020 to 2050 (Fiedler et al., in review). We then use the MACv2-SP data to provide estimates of the effective radiative effects of the anthropogenic aerosols for 2020 and 2050. Our forcing estimates are based on new atmosphere-only simulations with the CMIP6 model EC-Earth3. The model uses MACv2-SP to represent aerosol-radiation and aerosol-cloud interactions including aerosol effects on cloud lifetime. For each anthropogenic aerosol pattern, we run EC-Earth3 simulations for fifty years to substantially reduce the impact of model-internal variability on the forcing estimate. Our results highlight: (1) a change of +0.04 Wm<sup>-2</sup> in the global mean effective radiative forcing of anthropogenic aerosols for 2020 due to the pandemic, which is small compared to the magnitude of internal variability, (2) a spread of -0.38 to -0.68 Wm<sup>-2</sup> for the effective radiative forcing associated with anthropogenic aerosols in 2050 depending on the recovery scenario in MACv2-SP, and (3) a more negative (stronger) anthropogenic aerosol forcing for a strong green than a moderate green development in 2050 due to higher ammonium emissions in a highly decarbonized society (Fiedler et al., in review). The new MACv2-SP data are now used in climate models participating in the model intercomparison project on the climate response to the COVID-19 crisis (Covid-MIP, Jones et al., in review, Lamboll et al., in review).</p><p><strong>References:</strong></p><p>Fiedler, S., Wyser, K., Joeri, R., and van Noije, T.: Radiative effects of reduced aerosol emissions during the COVID-19 pandemic and the future recovery, in review, [preprint] https://doi.org/10.1002/essoar.10504704.1.</p><p>Forster, P.M., Forster, H.I., Evans, M.J.&#160;et al.:&#160;Current and future global climate impacts resulting from COVID-19.&#160;Nat. Clim. Chang.&#160;10,&#160;913&#8211;919, 2020, https://doi.org/10.1038/s41558-020-0883-0.</p><p>Jones. C., Hickman, J., Rumbold, S., et al.: The Climate Response to Emissions Reductions due to COVID-19, Geophy. Res. Lett., in review.</p><p>Lamboll, R. D., Jones, C. D., Skeie, R. B., Fiedler, S., Samset, B. H., Gillett, N. P., Rogelj, J., and Forster, P. M.: Modifying emission scenario projections to account for the effects of COVID-19: protocol for Covid-MIP, in review, [preprint] https://doi.org/10.5194/gmd-2020-373.</p>

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Uncertainty in Aerosol Radiative Forcing Impacts the Simulated Global Monsoon in the 20th Century

10.5194/acp-2020-478 ◽

2020 ◽

Author(s):

Jonathan K. P. Shonk ◽

Andrew G. Turner ◽

Amulya Chevuturi ◽

Laura J. Wilcox ◽

Andrea J. Dittus ◽

...

Keyword(s):

Radiative Forcing ◽

Monsoon Rainfall ◽

Strong Relationship ◽

Dynamical Response ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Global Monsoon ◽

Monsoon Area ◽

Hemispheric Temperature ◽

Aerosol Emissions

Abstract. Anthropogenic aerosols are dominant drivers of historical monsoon rainfall change. However, large uncertainties in the radiative forcing associated with anthropogenic aerosol emissions, and the dynamical response to this forcing, lead to uncertainty in the simulated monsoon response. We use historical simulations in which aerosol emissions are scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to aerosol forcing uncertainty (−0.38 W m−2 to −1.50 W m−2). Hemispheric asymmetry in emissions generates a strong relationship between scaling factor and both hemispheric temperature contrast and meridional location of tropical rainfall. Increasing the scaling from 0.2 to 1.5 reduces the global monsoon area by 3 % and the global monsoon intensity by 2 % over the period 1950–2014, and switches the dominant influence on the 1950–1980 monsoon rainfall trend between greenhouse gas and aerosol. Regionally, aerosol scaling has a pronounced effect on Northern Hemisphere monsoon rainfall.

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Incorrect Asian aerosols affecting the attribution and projection of regional climate change in CMIP6 models

npj Climate and Atmospheric Science ◽

10.1038/s41612-020-00159-2 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Zhili Wang ◽

Lei Lin ◽

Yangyang Xu ◽

Huizheng Che ◽

Xiaoye Zhang ◽

...

Keyword(s):

Climate Change ◽

Radiative Forcing ◽

Impact Analysis ◽

Climate Model ◽

Regional Climate ◽

Eastern China ◽

Coupled Model ◽

Regional Climate Change ◽

Anthropogenic Aerosol ◽

Wide Range

AbstractAnthropogenic aerosol (AA) forcing has been shown as a critical driver of climate change over Asia since the mid-20th century. Here we show that almost all Coupled Model Intercomparison Project Phase 6 (CMIP6) models fail to capture the observed dipole pattern of aerosol optical depth (AOD) trends over Asia during 2006–2014, last decade of CMIP6 historical simulation, due to an opposite trend over eastern China compared with observations. The incorrect AOD trend over China is attributed to problematic AA emissions adopted by CMIP6. There are obvious differences in simulated regional aerosol radiative forcing and temperature responses over Asia when using two different emissions inventories (one adopted by CMIP6; the other from Peking university, a more trustworthy inventory) to driving a global aerosol-climate model separately. We further show that some widely adopted CMIP6 pathways (after 2015) also significantly underestimate the more recent decline in AA emissions over China. These flaws may bring about errors to the CMIP6-based regional climate attribution over Asia for the last two decades and projection for the next few decades, previously anticipated to inform a wide range of impact analysis.

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Climatic effects of 1950–2050 changes in US anthropogenic aerosols – Part 1: Aerosol trends and radiative forcing

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-24085-2011 ◽

2011 ◽

Vol 11 (8) ◽

pp. 24085-24125 ◽

Cited By ~ 8

Author(s):

E. M. Leibensperger ◽

L. J. Mickley ◽

D. J. Jacob ◽

W.-T. Chen ◽

J. H. Seinfeld ◽

...

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

Transport Model ◽

Circulation Model ◽

Anthropogenic Sources ◽

So2 Emissions ◽

Anthropogenic Aerosols ◽

Climatic Effects ◽

Anthropogenic Aerosol ◽

Direct Forcing

Abstract. We use the GEOS-Chem chemical transport model combined with the GISS general circulation model to calculate the aerosol direct and indirect (warm cloud) radiative forcings from US anthropogenic sources over the 1950–2050 period, based on historical emission inventories and future projections from the IPCC A1B scenario. The aerosol simulation is evaluated with observed spatial distributions and 1980–2010 trends of aerosol concentrations and wet deposition in the contiguous US. The radiative forcing from US anthropogenic aerosols is strongly localized over the eastern US. We find that it peaked in 1970–1990, with values over the eastern US (east of 100° W) of −2.0 W m−2 for direct forcing including contributions from sulfate (−2.0 W m−2), nitrate (−0.2 W m−2), organic carbon (−0.2 W m−2), and black carbon (+0.4 W m−2). The aerosol indirect effect is of comparable magnitude to the direct forcing. We find that the forcing declined sharply from 1990 to 2010 (by 0.8 W m−2 direct and 1.0 W m−2 indirect), mainly reflecting decreases in SO2 emissions, and project that it will continue declining post-2010 but at a much slower rate since US SO2 emissions have already declined by almost 60 % from their peak. This suggests that much of the warming effect of reducing US anthropogenic aerosol sources may have already been realized by 2010, however some additional warming is expected through 2020. The small positive radiative forcing from US BC emissions (+0.3 W m−2 over the eastern US in 2010) suggests that an emission control strategy focused on BC would have only limited climate benefit.

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