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

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is a new configuration of the Community Atmosphere Model version 5.3 (CAM5.3) in which the default aerosol module has been replaced by the two-Moment, Multi-Modal, Mixing-state-resolving Aerosol model for Research of Climate (MARC).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 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 lifetimes, 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), and a configuration using the modal aerosol module with seven log-normal modes (MAM7). Compared with MAM3 and MAM7, we find that MARC produces stronger cooling via the direct radiative effect, the shortwave cloud radiative effect, and the surface albedo radiative effect; similarly, MARC produces stronger warming via the longwave cloud radiative effect. Overall, MARC produces a global mean net ERF of -1.79±0.03 W m−2, which is stronger than the global mean net ERF of -1.57±0.04 W m−2 produced by MAM3 and -1.53±0.04 W m−2 produced by MAM7. The regional distribution of ERF also differs between MARC and MAM3, largely due to differences in the regional distribution of the shortwave cloud radiative effect. We conclude that the specific representation of aerosols in global climate models, including aerosol mixing state, has important implications for climate modelling.

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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.

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Implications of aerosol-induced snow darkening on regional hydroclimate over the Himalayas

10.5194/egusphere-egu21-11972 ◽

2021 ◽

Author(s):

Vijayakumar Sivadasan Nair ◽

Usha Keshav Hasyagar ◽

Surendran Nair Suresh Babu

Keyword(s):

South Asia ◽

Climate Model ◽

Hydrological Cycle ◽

Monsoon Season ◽

Radiation Balance ◽

Western Himalayas ◽

Radiative Effect ◽

Anthropogenic Aerosols ◽

Snow Albedo ◽

Snow Cover Extent

The snow-covered mountains of Himalayas are known to play a crucial role in the hydrology of South Asia and are known as the &#8220;Asian water tower&#8221;. Despite the high elevations, the transport of anthropogenic aerosols from south Asia and desert dust from west Asia plays a significant role in directly and indirectly perturbing the radiation balance and hydrological cycle over the region. Absorbing aerosols like black carbon (BC) and dust deposited on the snow surface reduces the albedo of the Himalayan snow significantly (snow darkening or snow albedo effect). Using a Regional Climate Model (RegCM-4.6.0) coupled with SNow, ICe and Aerosol Radiation (SNICAR) module, the implications of aerosol-induced snow darkening on the regional hydroclimate of the Himalayas are investigated in this study. The aerosols deposited on snow shows a distinct regional heterogeneity. The albedo reduction due to aerosols shows a west to east gradient during pre-monsoon season and this results in the positive radiative effect of about 29 Wm-2, 17 Wm-2 and 5 Wm-2 over western, central and eastern Himalayas respectively. The reduction in the snow albedo also results in the sign reversal of the aerosol direct radiative effect i.e., from warming to cooling at the top of the atmosphere during pre-monsoon season. The excess solar energy trapped at the surface due to snow darkening warms the surface (0.66-1.9 K) and thus decreases the snow cover extent significantly. This results in the reduction of the number of snow-covered days by more than a month over the western Himalayas and about 10 &#8211; 15 days over the central Himalayas. The early snowmelt due to aerosol-induced snow darkening results in the increase of runoff throughout the melting season. Therefore, the present study highlights the heterogeneous response of aerosol induced snow albedo feedbacks over the Himalayan region and its impact on the snowpack and hydrology, which has further implications on the freshwater availability over the region.

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The aerosol-climate model ECHAM5-HAM

Atmospheric Chemistry and Physics ◽

10.5194/acp-5-1125-2005 ◽

2005 ◽

Vol 5 (4) ◽

pp. 1125-1156 ◽

Cited By ~ 787

Author(s):

P. Stier ◽

J. Feichter ◽

S. Kinne ◽

S. Kloster ◽

E. Vignati ◽

...

Keyword(s):

Size Distribution ◽

Climate Model ◽

Normal Modes ◽

Anthropogenic Activity ◽

Climate Modelling ◽

Extensive Evaluation ◽

Wide Range ◽

Log Normal ◽

Year 2000

Abstract. The aerosol-climate modelling system ECHAM5-HAM is introduced. It is based on a flexible microphysical approach and, as the number of externally imposed parameters is minimised, allows the application in a wide range of climate regimes. ECHAM5-HAM predicts the evolution of an ensemble of microphysically interacting internally- and externally-mixed aerosol populations as well as their size-distribution and composition. The size-distribution is represented by a superposition of log-normal modes. In the current setup, the major global aerosol compounds sulfate (SU), black carbon (BC), particulate organic matter (POM), sea salt (SS), and mineral dust (DU) are included. The simulated global annual mean aerosol burdens (lifetimes) for the year 2000 are for SU: 0.80 Tg(S) (3.9 days), for BC: 0.11 Tg (5.4 days), for POM: 0.99 Tg (5.4 days), for SS: 10.5 Tg (0.8 days), and for DU: 8.28 Tg (4.6 days). An extensive evaluation with in-situ and remote sensing measurements underscores that the model results are generally in good agreement with observations of the global aerosol system. The simulated global annual mean aerosol optical depth (AOD) is with 0.14 in excellent agreement with an estimate derived from AERONET measurements (0.14) and a composite derived from MODIS-MISR satellite retrievals (0.16). Regionally, the deviations are not negligible. However, the main patterns of AOD attributable to anthropogenic activity are reproduced.

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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.

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New approaches to quantifying aerosol influence on the cloud radiative effect

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1514035112 ◽

2016 ◽

Vol 113 (21) ◽

pp. 5812-5819 ◽

Cited By ~ 31

Author(s):

Graham Feingold ◽

Allison McComiskey ◽

Takanobu Yamaguchi ◽

Jill S. Johnson ◽

Kenneth S. Carslaw ◽

...

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

General Circulation Models ◽

Shortwave Radiation ◽

Emergent Properties ◽

Radiative Effect ◽

Aerosol Composition ◽

Aerosol Cloud ◽

Cloud Radiative Effect ◽

Aerosol Cloud Interactions

The topic of cloud radiative forcing associated with the atmospheric aerosol has been the focus of intense scrutiny for decades. The enormity of the problem is reflected in the need to understand aspects such as aerosol composition, optical properties, cloud condensation, and ice nucleation potential, along with the global distribution of these properties, controlled by emissions, transport, transformation, and sinks. Equally daunting is that clouds themselves are complex, turbulent, microphysical entities and, by their very nature, ephemeral and hard to predict. Atmospheric general circulation models represent aerosol−cloud interactions at ever-increasing levels of detail, but these models lack the resolution to represent clouds and aerosol−cloud interactions adequately. There is a dearth of observational constraints on aerosol−cloud interactions. We develop a conceptual approach to systematically constrain the aerosol−cloud radiative effect in shallow clouds through a combination of routine process modeling and satellite and surface-based shortwave radiation measurements. We heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.

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Modelling sea salt aerosol and its direct and indirect effects on climate

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-14939-2007 ◽

2007 ◽

Vol 7 (5) ◽

pp. 14939-14987 ◽

Cited By ~ 1

Author(s):

X. Ma ◽

K. von Salzen ◽

J. Li

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Sea Salt ◽

Size Distributions ◽

Size Dependent ◽

Sea Salt Aerosol ◽

Direct Forcing ◽

Log Normal

Abstract. A size-dependent sea salt aerosol parameterization was developed based on the piecewise log-normal approximation (PLA) for aerosol size distributions. Results of this parameterization from simulations with a global climate model produce good agreement with observations at the surface and for vertically-integrated volume size distributions. The global and annual mean of the sea salt burden is 10.1 mg m−2. The direct radiative forcing is calculated to be −1.52 and −0.60 W m−2 for clear sky and all sky, respectively. The first indirect radiative forcing is about twice as large as the direct forcing for all-sky (−1.34 W m−2). The results also show that the total indirect forcing of sea salt is −2.9 W m−2 if climatic feedbacks are taken into account. The sensitivity of the forcings to changes in the burdens and sizes of sea salt particles was also investigated based on additional simulations with a different sea salt source function.

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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.

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How important are future marine and shipping aerosol emissions in a warming Arctic summer and autumn?

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-10521-2018 ◽

2018 ◽

Vol 18 (14) ◽

pp. 10521-10555 ◽

Cited By ~ 8

Author(s):

Anina Gilgen ◽

Wan Ting Katty Huang ◽

Luisa Ickes ◽

David Neubauer ◽

Ulrike Lohmann

Keyword(s):

Sea Ice ◽

Radiative Forcing ◽

Aerosol Particles ◽

Late Summer ◽

The Arctic ◽

Ship Emissions ◽

Early Autumn ◽

Cloud Radiative Effect ◽

Aerosol Emissions ◽

Aerosol Radiative

Abstract. Future sea ice retreat in the Arctic in summer and autumn is expected to affect both natural and anthropogenic aerosol emissions: sea ice acts as a barrier between the ocean and the atmosphere, and reducing it increases dimethyl sulfide and sea salt emissions. Additionally, a decrease in the area and thickness of sea ice could lead to enhanced Arctic ship traffic, for example due to shorter routes of cargo ships. Changes in the emissions of aerosol particles can then influence cloud properties, precipitation, surface albedo, and radiation. Next to changes in aerosol emissions, clouds will also be affected by increases in Arctic temperatures and humidities. In this study, we quantify how future aerosol radiative forcings and cloud radiative effects might change in the Arctic in late summer (July–August) and early autumn (September–October). Simulations were conducted for the years 2004 and 2050 with the global aerosol–climate model ECHAM6-HAM2. For 2050, simulations with and without additional ship emissions in the Arctic were carried out to quantify the impact of these emissions on the Arctic climate. In the future, sea salt as well as dimethyl sulfide emissions and burdens will increase in the Arctic. The increase in cloud condensation nuclei, which is due to changes in aerosol particles and meteorology, will enhance cloud droplet number concentrations over the Arctic Ocean (+10 % in late summer and +29 % in early autumn; in-cloud values averaged between 75 and 90∘ N). Furthermore, both liquid and total water path will increase (+10 % and +8 % in late summer; +34 % and +26 % in early autumn) since the specific humidity will be enhanced due to higher temperatures and the exposure of the ocean's surface. Changes in both aerosol radiative forcings and cloud radiative effects at the top of the atmosphere will not be dominated by the aerosol particles and clouds themselves but by the decrease in surface albedo (and by the increase in surface temperature for the longwave cloud radiative effect in early autumn). Mainly due to the reduction in sea ice, the aerosol radiative forcing will become less positive (decreasing from 0.53 to 0.36 W m−2 in late summer and from 0.15 to 0.11 W m−2 in early autumn). The decrease in sea ice is also mainly responsible for changes in the net cloud radiative effect, which will become more negative in late summer (changing from −36 to −46 W m−2). Therefore, the cooling component of both aerosols and clouds will gain importance in the future. We found that future Arctic ship emissions related to transport and oil and gas extraction (Peters et al., 2011) will not have a large impact on clouds and radiation: changes in aerosols only become significant when we increase these ship emissions by a factor of 10. However, even with 10-fold ship emissions, the net aerosol radiative forcing shows no significant changes. Enhanced black carbon deposition on snow leads to a locally significant but very small increase in radiative forcing over the central Arctic Ocean in early autumn (no significant increase for average between 75 and 90∘ N). Furthermore, the 10-fold higher ship emissions increase the optical thickness and lifetime of clouds in late summer (net cloud radiative effect changing from −48 to −52 W m−2). These aerosol–cloud effects have a considerably larger influence on the radiative forcing than the direct effects of particles (both aerosol particles in the atmosphere and particles deposited on snow). In summary, future ship emissions of aerosols and their precursor gases might have a net cooling effect, which is small compared to other changes in future Arctic climate such as those caused by the decrease in surface albedo.

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If Anthropogenic CO2 Emissions Cease, Will Atmospheric CO2 Concentration Continue to Increase?

Journal of Climate ◽

10.1175/jcli-d-12-00751.1 ◽

2013 ◽

Vol 26 (23) ◽

pp. 9563-9576 ◽

Cited By ~ 12

Author(s):

Andrew H. MacDougall ◽

Michael Eby ◽

Andrew J. Weaver

Keyword(s):

Greenhouse Gases ◽

Radiative Forcing ◽

Climate Model ◽

Carbon Sources ◽

Co2 Concentration ◽

Earth System ◽

Terrestrial Source ◽

The University ◽

Aerosol Emissions ◽

Over Time

If anthropogenic CO2 emissions were to suddenly cease, the evolution of the atmospheric CO2 concentration would depend on the magnitude and sign of natural carbon sources and sinks. Experiments using Earth system models indicate that the overall carbon sinks dominate, such that upon the cessation of anthropogenic emissions, atmospheric CO2 levels decrease over time. However, these models have typically neglected the permafrost carbon pool, which has the potential to introduce an additional terrestrial source of carbon to the atmosphere. Here, the authors use the University of Victoria Earth System Climate Model (UVic ESCM), which has recently been expanded to include permafrost carbon stocks and exchanges with the atmosphere. In a scenario of zeroed CO2 and sulfate aerosol emissions, whether the warming induced by specified constant concentrations of non-CO2 greenhouse gases could slow the CO2 decline following zero emissions or even reverse this trend and cause CO2 to increase over time is assessed. It is found that a radiative forcing from non-CO2 gases of approximately 0.6 W m−2 results in a near balance of CO2 emissions from the terrestrial biosphere and uptake of CO2 by the oceans, resulting in near-constant atmospheric CO2 concentrations for at least a century after emissions are eliminated. At higher values of non-CO2 radiative forcing, CO2 concentrations increase over time, regardless of when emissions cease during the twenty-first century. Given that the present-day radiative forcing from non-CO2 greenhouse gases is about 0.95 W m−2, the results suggest that if all CO2 and aerosols emissions were eliminated without also decreasing non-CO2 greenhouse gas emissions CO2 levels would increase over time, resulting in a small increase in climate warming associated with this positive permafrost–carbon feedback.

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Comparison of Climate Response to Anthropogenic Aerosol versus Greenhouse Gas Forcing: Distinct Patterns

Journal of Climate ◽

10.1175/jcli-d-16-0106.1 ◽

2016 ◽

Vol 29 (14) ◽

pp. 5175-5188 ◽

Cited By ~ 38

Author(s):

Hai Wang ◽

Shang-Ping Xie ◽

Qinyu Liu

Keyword(s):

Northern Hemisphere ◽

Radiative Forcing ◽

Climate Model ◽

East Asian Monsoon ◽

Climate Response ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Asian Monsoon Region ◽

Surface Temperature Change ◽

Aerosol Forcing

Abstract Spatial patterns of climate response to changes in anthropogenic aerosols and well-mixed greenhouse gases (GHGs) are investigated using climate model simulations for the twentieth century. The climate response shows both similarities and differences in spatial pattern between aerosol and GHG runs. Common climate response between aerosol and GHG runs tends to be symmetric about the equator. This work focuses on the distinctive patterns that are unique to the anthropogenic aerosol forcing. The tropospheric cooling induced by anthropogenic aerosols is locally enhanced in the midlatitude Northern Hemisphere with a deep vertical structure around 40°N, anchoring a westerly acceleration in thermal wind balance. The aerosol-induced negative radiative forcing in the Northern Hemisphere requires a cross-equatorial Hadley circulation to compensate interhemispheric energy imbalance in the atmosphere. Associated with a southward shift of the intertropical convergence zone, this interhemispheric asymmetric mode is unique to aerosol forcing and absent in GHG runs. Comparison of key climate response pattern indices indicates that the aerosol forcing dominates the interhemispheric asymmetric climate response in historical all-forcing simulations, as well as regional precipitation change such as the drying trend over the East Asian monsoon region. While GHG forcing dominates global mean surface temperature change, its effect is on par with and often opposes the aerosol effect on precipitation, making it difficult to detect anthropogenic change in rainfall from historical observations.

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