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

<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>

Download Full-text

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-14903-2020 ◽

2020 ◽

Vol 20 (23) ◽

pp. 14903-14915

Author(s):

Jonathan K. P. Shonk ◽

Andrew G. Turner ◽

Amulya Chevuturi ◽

Laura J. Wilcox ◽

Andrea J. Dittus ◽

...

Keyword(s):

Radiative Forcing ◽

Monsoon Rainfall ◽

Scaling Factor ◽

Global Monsoon ◽

Tropical Rainfall ◽

Aerosol Forcing ◽

Monsoon Area ◽

Hemispheric Temperature ◽

Temperature Contrast ◽

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, as well as the dynamical response to this forcing, lead to uncertainty in the simulated monsoon response. We use historical simulations from the “SMURPHS” project, run using HadGEM3-GC3.1, in which the time-varying aerosol emissions are scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to historical aerosol forcing uncertainty (present-day versus preindustrial aerosol forcing in the range −0.38 to −1.50 W m−2). The hemispheric asymmetry in emissions generates a strong relationship between scaling factor and both hemispheric temperature contrast and meridional location of tropical rainfall. Averaged over the period 1950–2014, increasing the scaling factor from 0.2 to 1.5 reduces the hemispheric temperature contrast by 0.9 ∘C, reduces the tropical summertime land–sea temperature contrast by 0.3 ∘C and shifts tropical rainfall southwards by 0.28∘ of latitude. The result is a reduction in global monsoon area by 3 % and a reduction in global monsoon intensity by 2 %. Despite the complexity of the monsoon system, the monsoon properties presented above vary monotonically and roughly linearly across scalings. A switch in the dominant influence on the 1950–1980 monsoon rainfall trend between greenhouse gases and aerosol is identified as the scalings increase. Regionally, aerosol scaling has a pronounced effect on Northern Hemisphere monsoon rainfall, with the strongest influence on monsoon area and intensity located in the Asian sector, where local emissions are greatest.

Download Full-text

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>

Download Full-text

The Impacts of Aerosol Emissions on Historical Climate in UKESM1

Atmosphere ◽

10.3390/atmos11101095 ◽

2020 ◽

Vol 11 (10) ◽

pp. 1095

Author(s):

Jeongbyn Seo ◽

Sungbo Shim ◽

Sang-Hoon Kwon ◽

Kyung-On Boo ◽

Yeon-Hee Kim ◽

...

Keyword(s):

Radiative Forcing ◽

Regional Climate ◽

Central China ◽

Historical Period ◽

Model Intercomparison ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Aerosol Emission ◽

Intercomparison Project ◽

Aerosol Emissions

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.

Download Full-text

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.

Download Full-text

Effective radiative forcing in the aerosol–climate model CAM5.3-MARC-ARG

10.5194/acp-2018-118 ◽

2018 ◽

Cited By ~ 1

Author(s):

Benjamin S. Grandey ◽

Daniel Rothenberg ◽

Alexander Avramov ◽

Qinjian Jin ◽

Hsiang-He Lee ◽

...

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Regional Distribution ◽

Radiative Effect ◽

Mixing State ◽

Anthropogenic Aerosols ◽

Effective Radiative Forcing ◽

Aerosol Module ◽

Aerosol Emissions ◽

Global Mean

Abstract. We quantify the effective radiative forcing (ERF) of anthropogenic aerosols modelled by the aerosol–climate model CAM5.3-MARC-ARG. CAM5.3-MARC-ARG is a new configuration of the Community Atmosphere Model version 5.3 (CAM5.3) in which the default aerosol module has been replaced by the two-Moment, Multi-Modal, Mixing-state-resolving Aerosol model for Research of Climate (MARC). CAM5.3-MARC-ARG uses the default ARG aerosol activation scheme, consistent with the default configuration of CAM5.3. We compute differences between simulations using year-1850 aerosol emissions and simulations using year-2000 aerosol emissions in order to assess the radiative effects of anthropogenic aerosols. We compare the aerosol column burdens, cloud properties, and radiative effects produced by CAM5.3-MARC-ARG with those produced by the default configuration of CAM5.3, which uses the modal aerosol module with three log-normal modes (MAM3). Compared with MAM3, we find that MARC produces stronger cooling via the direct radiative effect, stronger cooling via the surface albedo radiative effect, and stronger warming via the cloud longwave radiative effect. The global mean cloud shortwave radiative effect is similar between MARC and MAM3, although the regional distributions differ. Overall, MARC produces a global mean net ERF of −1.75 ± 0.04 W m−2, which is stronger than the global mean net ERF of −1.57 ± 0.04 W m−2 produced by MAM3. The regional distribution of ERF also differs between MARC and MAM3, largely due to differences in the regional distribution of the cloud shortwave radiative effect. We conclude that the specific representation of aerosols in global climate models, including aerosol mixing state, has important implications for climate modelling.

Download Full-text

Contrasting the direct radiative effect and direct radiative forcing of aerosols

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-5513-2014 ◽

2014 ◽

Vol 14 (11) ◽

pp. 5513-5527 ◽

Cited By ~ 105

Author(s):

C. L. Heald ◽

D. A. Ridley ◽

J. H. Kroll ◽

S. R. H. Barrett ◽

K. E. Cady-Pereira ◽

...

Keyword(s):

Energy Balance ◽

Radiative Forcing ◽

Transport Model ◽

Radiative Transfer Model ◽

Transfer Model ◽

Radiative Effect ◽

Chemical Transport Model ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Direct Radiative Forcing

Abstract. The direct radiative effect (DRE) of aerosols, which is the instantaneous radiative impact of all atmospheric particles on the Earth's energy balance, is sometimes confused with the direct radiative forcing (DRF), which is the change in DRE from pre-industrial to present-day (not including climate feedbacks). In this study we couple a global chemical transport model (GEOS-Chem) with a radiative transfer model (RRTMG) to contrast these concepts. We estimate a global mean all-sky aerosol DRF of −0.36 Wm−2 and a DRE of −1.83 Wm−2 for 2010. Therefore, natural sources of aerosol (here including fire) affect the global energy balance over four times more than do present-day anthropogenic aerosols. If global anthropogenic emissions of aerosols and their precursors continue to decline as projected in recent scenarios due to effective pollution emission controls, the DRF will shrink (−0.22 Wm−2 for 2100). Secondary metrics, like DRE, that quantify temporal changes in both natural and anthropogenic aerosol burdens are therefore needed to quantify the total effect of aerosols on climate.

Download Full-text

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

Journal of Climate ◽

10.1175/jcli-d-17-0034.1 ◽

2017 ◽

Vol 30 (16) ◽

pp. 6585-6589 ◽

Cited By ~ 4

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.

Download Full-text

Drier North American Monsoon in Contrast to Asian–African Monsoon under Global Warming

Journal of Climate ◽

10.1175/jcli-d-20-0189.1 ◽

2020 ◽

Vol 33 (22) ◽

pp. 9801-9816

Author(s):

Chao He ◽

Tim Li ◽

Wen Zhou

Keyword(s):

North American ◽

Radiative Forcing ◽

Monsoon Rainfall ◽

Summer Monsoon Rainfall ◽

North American Monsoon ◽

Global Monsoon ◽

African Monsoon ◽

High Emission ◽

Continental Area ◽

Sst Warming

AbstractSummer monsoon rainfall supplies over 55% of annual precipitation to global monsoon regions. As shown by more than 70% of models, including 30 models from CMIP5 and 30 models from CMIP6 under high-emission scenarios, North American (NAM) monsoon rainfall decreases in a warmer climate, in sharp contrast to the robust increase in Asian–African monsoon rainfall. A hierarchy of model experiments is analyzed to understand the mechanism for the reduced NAM monsoon rainfall in this study. Modeling evidence shows that the reduction of NAM monsoon rainfall is related to both direct radiative forcing of increased CO2 concentration and SST warming, manifested as fast and slow responses to abrupt CO2 quadrupling in coupled GCMs. A cyclone anomaly forms over the Eurasian–African continental area due to enhanced land–sea thermal contrast under increased CO2 concentration, and this leads to a subsidence anomaly on its western flank, suppressing the NAM monsoon rainfall. The SST warming acts to further reduce the rainfall over the NAM monsoon region, and the El Niño–like SST warming pattern with enhanced SST warming over the equatorial Pacific plays a key role in suppressing NAM rainfall, whereas relative cooling over the subtropical North Atlantic has no contribution. A positive feedback between monsoon precipitation and atmospheric circulation helps to amplify the responses of monsoon rainfall.

Download Full-text

Cloudy sky contributions to the direct aerosol effect

10.5194/acp-2019-1051 ◽

2019 ◽

Cited By ~ 1

Author(s):

Gunnar Myhre ◽

Bjørn H. Samset ◽

Christian W. Mohr ◽

Kari Alterskjær ◽

Yves Balkanski ◽

...

Keyword(s):

Radiative Forcing ◽

Single Scattering ◽

Observational Methods ◽

Anthropogenic Aerosols ◽

Uncertainty Range ◽

Clear Sky ◽

Aerosol Effect ◽

Analysis Of Results ◽

Cloud Radiative Effects ◽

Aerosol Emissions

Abstract. The radiative forcing of the aerosol-radiation interaction can be decomposed into clear sky and cloudy sky portions. Two sets of multi-model simulations within AeroCom, combined with observational methods, and the time evolution of aerosol emissions over the industrial era show that the contribution from cloudy sky regions is likely weak. A mean of the simulations considered is 0.01 ± 0.1 W m−2. Multivariate data analysis of results from AeroCom Phase II shows that many factors influence the strength of the cloudy sky contribution to the forcing of the aerosol-radiation interaction. Overall, single scattering albedo of anthropogenic aerosols and the interaction of aerosols with the shortwave cloud radiative effects are found to be important factors. A more dedicated focus on the contribution from the cloud free and cloud covered sky fraction respectively to the aerosol-radiation interaction will benefit the quantification of the radiative forcing and its uncertainty range.

Download Full-text