Multidecadal trends in aerosol radiative forcing over the Arctic: Contribution of changes in anthropogenic aerosol to Arctic warming since 1980

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.

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

Geoscientific Model Development ◽

10.5194/gmd-10-433-2017 ◽

2017 ◽

Vol 10 (1) ◽

pp. 433-452 ◽

Cited By ~ 57

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.

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WRF-Chem simulations of aerosols and anthropogenic aerosol radiative forcing in East Asia

Atmospheric Environment ◽

10.1016/j.atmosenv.2014.04.038 ◽

2014 ◽

Vol 92 ◽

pp. 250-266 ◽

Cited By ~ 57

Author(s):

Yi Gao ◽

Chun Zhao ◽

Xiaohong Liu ◽

Meigen Zhang ◽

L. Ruby Leung

Keyword(s):

East Asia ◽

Radiative Forcing ◽

Anthropogenic Aerosol ◽

Aerosol Radiative Forcing ◽

Aerosol Radiative

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Opportunistic Experiments to Constrain Aerosol Effective Radiative Forcing

10.5194/acp-2021-559 ◽

2021 ◽

Author(s):

Matthew Christensen ◽

Andrew Gettelman ◽

Jan Cermak ◽

Guy Dagan ◽

Michael Diamond ◽

...

Keyword(s):

Forest Fires ◽

Radiative Forcing ◽

Volcanic Eruptions ◽

Point Sources ◽

Natural Experiments ◽

Experimental Conditions ◽

Anthropogenic Aerosol ◽

Aerosol Radiative Forcing ◽

Wide Range ◽

Aerosol Radiative

Abstract. Aerosol-cloud interactions (ACI) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The non-linearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can also be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well defined sources provide “opportunistic experiments” (also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatio-temporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite data sets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Opportunistic experiments have significantly improved process level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus, demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change.

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ANTHROPOGENIC AEROSOL RADIATIVE FORCING IN THE INDO-GANGETIC BASIN

Advances in Geosciences ◽

10.1142/9789812836120_0011 ◽

2010 ◽

pp. 123-136

Author(s):

SAGNIK DEY ◽

S. N. TRIPATHI

Keyword(s):

Radiative Forcing ◽

Anthropogenic Aerosol ◽

Aerosol Radiative Forcing ◽

Aerosol Radiative

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Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1602360113 ◽

2016 ◽

Vol 113 (43) ◽

pp. 12053-12058 ◽

Cited By ~ 56

Author(s):

Hamish Gordon ◽

Kamalika Sengupta ◽

Alexandru Rap ◽

Jonathan Duplissy ◽

Carla Frege ◽

...

Keyword(s):

Radiative Forcing ◽

Cloud Condensation Nuclei ◽

Large Fraction ◽

Particle Formation ◽

Lower Atmosphere ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Aerosol Radiative Forcing ◽

Cloud Albedo ◽

Aerosol Radiative

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol–cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20–100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m−2 (27%) to −0.60 W m−2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes.

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

10.5194/acp-2017-1007 ◽

2017 ◽

Cited By ~ 2

Author(s):

Anina Gilgen ◽

Wan Ting Katty Huang ◽

Luisa Ickes ◽

David Neubauer ◽

Ulrike Lohmann

Keyword(s):

Sea Ice ◽

Radiative Forcing ◽

Surface Albedo ◽

Aerosol Particles ◽

Late Summer ◽

The Arctic ◽

Ship Emissions ◽

Aerosol Radiative Forcing ◽

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 sulphide and sea salt emissions. A decrease in the area and thickness of sea ice could in addition lead to enhanced Arctic ship traffic, e.g. to shorten the paths 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 particles, clouds will also be affected by increases in Arctic temperatures and humidities. In this study, we quantified how future aerosol radiative forcing, aerosol-cloud interactions, 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. In 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. We found that aerosol number concentrations in the Arctic will generally increase in the future due to enhanced emissions of sea salt as well as dimethyl sulphide. The increase in cloud condensation nuclei will enhance cloud droplet number concentrations over the Arctic Ocean. Furthermore, both liquid and total water content will increase 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). Due to the reduction in sea ice, the aerosol radiative forcing will become less positive and the cloud radiative effect more negative, i.e. the cooling component of both will gain importance in the future. We found that future Arctic ship emissions related to transport and oil/gas extraction (Peters et al., 2011, ACP) will not have a large impact on clouds and radiation: changes in aerosol concentrations only become significant when we increase these ship emissions by a factor of ten. The net aerosol radiative forcing shows only small, non-significant changes. Enhanced black carbon deposition on snow leads to a significant but very small warming over the central Arctic Ocean in early autumn. Furthermore, the tenfold higher ship emissions increase the optical thickness of low clouds and thus induce a small Twomey effect (cooling) in late summer. This Twomey effect has a considerably larger influence on temperature than the direct effect of particles (both aerosol particles in the atmosphere and particles deposited on snow), but it is more uncertain because of the large variability of clouds. In summary, future ship emissions 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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Global fine-mode aerosol radiative effect, as constrained by comprehensive observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-8071-2016 ◽

2016 ◽

Vol 16 (13) ◽

pp. 8071-8080 ◽

Cited By ~ 8

Author(s):

Chul E. Chung ◽

Jung-Eun Chu ◽

Yunha Lee ◽

Twan van Noije ◽

Hwayoung Jeoung ◽

...

Keyword(s):

Radiative Forcing ◽

Radiative Effect ◽

Anthropogenic Aerosols ◽

Anthropogenic Aerosol ◽

Radiative Balance ◽

Aerosol Radiative Forcing ◽

Fine Mode ◽

Natural Aerosols ◽

Fine Mode Aerosol ◽

Aerosol Radiative

Abstract. Aerosols directly affect the radiative balance of the Earth through the absorption and scattering of solar radiation. Although the contributions of absorption (heating) and scattering (cooling) of sunlight have proved difficult to quantify, the consensus is that anthropogenic aerosols cool the climate, partially offsetting the warming by rising greenhouse gas concentrations. Recent estimates of global direct anthropogenic aerosol radiative forcing (i.e., global radiative forcing due to aerosol–radiation interactions) are −0.35 ± 0.5 W m−2, and these estimates depend heavily on aerosol simulation. Here, we integrate a comprehensive suite of satellite and ground-based observations to constrain total aerosol optical depth (AOD), its fine-mode fraction, the vertical distribution of aerosols and clouds, and the collocation of clouds and overlying aerosols. We find that the direct fine-mode aerosol radiative effect is −0.46 W m−2 (−0.54 to −0.39 W m−2). Fine-mode aerosols include sea salt and dust aerosols, and we find that these natural aerosols result in a very large cooling (−0.44 to −0.26 W m−2) when constrained by observations. When the contribution of these natural aerosols is subtracted from the fine-mode radiative effect, the net becomes −0.11 (−0.28 to +0.05) W m−2. This net arises from total (natural + anthropogenic) carbonaceous, sulfate and nitrate aerosols, which suggests that global direct anthropogenic aerosol radiative forcing is less negative than −0.35 W m−2.

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

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-5563-2008 ◽

2008 ◽

Vol 8 (2) ◽

pp. 5563-5627 ◽

Cited By ~ 4

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.

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