Relative Importance of Greenhouse Gases, Sulfate, Organic Carbon, and Black Carbon Aerosol for South Asian Monsoon Rainfall Changes

Westervelt, Daniel M.; You, Yujia; Li, Xiaoqiong; Ting, Mingfang; Lee, Dong Eun; Ming, Yi

doi:10.1029/2020gl088363

Cited by 18 publications

(9 citation statements)

References 63 publications

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“…There are often questions of how well GCMs can simulate the Indian monsoon since their spatial resolution may be too coarse to resolve the complex orography of India and the surrounding regions (Prell and Kutzbach, 1992). Additionally, representation of cloud microphysical processes is a known limitation of GCMs (e.g., Wilcox et al, 2015). We find a large intermodel spread in cloud profile and precipitation changes in the various BC emissions scenarios studied here.…”

Section: Discussionmentioning

confidence: 78%

“…The issue with many of these studies is that they focus on individual models. There is a large spread in the precipitation response across models reflecting differing representations of cloud and aerosol processes (e.g., Wilcox et al, 2015), factors that may bias results given the already complex nature of modeling precipitation over India (Ramanathan et al, 2005;Bollasina et al, 2011;Turner and Annamalai, 2012;Ramesh and Goswami, 2014;Paul et al, 2016;Saha and Ghosh, 2019). Multimodel ensembles can improve our understanding and help constrain uncertainty about the impacts of different aerosol constituents on the monsoon.…”

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confidence: 99%

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Sensitivity of modeled Indian monsoon to Chinese and Indian aerosol emissions

et al. 2021

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Abstract. The South Asian summer monsoon supplies over 80 % of India's precipitation. Industrialization over the past few decades has resulted in severe aerosol pollution in India. Understanding monsoonal sensitivity to aerosol emissions in general circulation models (GCMs) could improve predictability of observed future precipitation changes. The aims here are (1) to assess the role of aerosols in India's monsoon precipitation and (2) to determine the roles of local and regional emissions. For (1), we study the Precipitation Driver Response Model Intercomparison Project experiments. We find that the precipitation response to changes in black carbon is highly uncertain with a large intermodel spread due in part to model differences in simulating changes in cloud vertical profiles. Effects from sulfate are clearer; increased sulfate reduces Indian precipitation, a consistency through all of the models studied here. For (2), we study bespoke simulations, with reduced Chinese and/or Indian emissions in three GCMs. A significant increase in precipitation (up to ∼20 %) is found only when both countries' sulfur emissions are regulated, which has been driven in large part by dynamic shifts in the location of convective regions in India. These changes have the potential to restore a portion of the precipitation losses induced by sulfate forcing over the last few decades.

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Section: Discussionmentioning

confidence: 78%

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confidence: 99%

Sensitivity of modeled Indian monsoon to Chinese and Indian aerosol emissions

et al. 2021

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“…Aerosols can also perturb cloud properties via aerosol-cloud interactions (ACI); an increase in aerosol availability may enhance cloud brightness, reducing surface fluxes, and suppress the warm rain process. The widespread emission of SU precursors in South and East Asia weakens the meridional temperature gradient and associated ASM circulation and precipitation [19][20][21], whilst BC emissions may promote anomalous convection and a redistribution of heat and moisture, changing the distribution of precipitation and the onset of the ASM [22][23][24][25]. Although the instantaneous responses to SU and BC are different the net response to aerosol is an overall weakening of the ASM driven by the surface cooling that both species exert [26].…”

Section: Introductionmentioning

confidence: 99%

Nonlinear response of Asian summer monsoon precipitation to emission reductions in South and East Asia

Herbert

Wilcox

Joshi

et al. 2021

Environ. Res. Lett.

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Anthropogenic aerosols over South and East Asia currently have a stronger impact on the Asian Summer Monsoon (ASM) than greenhouse gas emissions, yet projected aerosol emission changes in these regions are subject to considerable uncertainties such as timescale, location, emission type, and even the sign of the change. We use a circulation/climate model with idealised aerosol distributions to demonstrate that the sum of ASM responses to aerosol emission reductions in each region is very different to the response to simultaneous reductions in both regions, implying the ASM response to aerosol emissions reductions is highly nonlinear. The phenomenon is independent of whether aerosols are scattering or absorbing, and results from interaction of induced atmospheric circulation changes. The nonlinearity from interactions between aerosol forcing from different regions represents a new source of uncertainty in projections of ASM changes over the next 30-40 years, and may limit the utility of country-dependent aerosol trajectories when considering their Asia-wide effects, though we recommend further work to establish whether the nonlinearity is buffered by other drivers. To understand likely changes in the ASM due to aerosol reductions, countries will need to accurately take account of emissions reductions from across the wider region, rather than approximating them using simple scenarios and emulators. The nonlinearity in the response to forcing therefore presents a regional public goods issue for countries affected by the ASM, as the costs and benefits of aerosol emissions reductions are not internalised; in fact, forcings from different countries such as India and China work jointly to determine outcomes across the region.

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“…For example, the 20th century buildup of AAs is associated with a southward displacement of the Intertropical Convergence Zone (ITCZ; Hwang et al 2013 and the mid-1980s Sahel and Amazonia droughts (Ackerley et al 2011, Chang et al 2011. The buildup of AAs has also been linked to weakening of the South and East Asian monsoons (Bollasina et al 2011, Li et al 2015, Lau and Kim 2017, Undorf et al 2018, Westervelt et al 2020. Similarly, the projected future reduction in AAs has been linked to opposite responses, including a northward shift of the ITCZ (Allen 2015, Rotstayn et al 2015 and associated increases in East and West Africa rainfall (Scannell et al 2019), and increases in Asian monsoon precipitation (Wilcox et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Anthropogenic aerosol impacts on Pacific Coast precipitation in CMIP6 models

Allen

Zhao

2022

Environ. Res.: Climate

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Studies show anthropogenic aerosols (AAs) can perturb regional precipitation, including the tropical rain belt and monsoons of the Northern Hemisphere (NH). In the NH mid-latitudes, however, the impact of AAs on regional climate and precipitation remains uncertain. This work investigates the influence of AAs on wintertime precipitation along the North American Pacific Coast using models from the Coupled Model Intercomparison Project phase 6 (CMIP6). Over the early to mid-20th century, when U.S. and European AA and precursor gas emissions rapidly increased, a robust wintertime precipitation dipole pattern exists in CMIP6 all-forcing and AA-only forcing simulations, with wetting of the southern Pacific Coast (southward of 40N) and drying to the north. A corresponding dynamical dipole pattern also occurs--including strengthening of the east Pacific jet southward of 40N and weakening to the north--which is related to a Rossby wave teleconnection that emanates out of the tropical Pacific. Over the 21st century, when AAs are projected to decrease, an opposite hydro-dynamic dipole pattern occurs, including drying southward of 40N (including California) and wetting to the north. Although Pacific Coast precipitation is dominated by natural variability, good multi-model agreement in the forced component of Pacific Coast precipitation change exists, with the AA pattern (north south dipole) dominating the greenhouse gas (uniform) pattern in the historical all-forcing simulations. A high level of agreement in individual model-realization trends also exists, particularly for the early part of the 20th century, suggesting a robustness to the human signature on Pacific Coast precipitation changes. Thus, historical precipitation responses along the Pacific Coast are likely to have been driven by a mixture of natural variability and forced changes. Natural variations appear to drive a large fraction of this change, but human influences (i.e.,~aerosols) are likely to have preconditioned the variability of the climate in this region.

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Relative Importance of Greenhouse Gases, Sulfate, Organic Carbon, and Black Carbon Aerosol for South Asian Monsoon Rainfall Changes

Cited by 18 publications

References 63 publications

Sensitivity of modeled Indian monsoon to Chinese and Indian aerosol emissions

Sensitivity of modeled Indian monsoon to Chinese and Indian aerosol emissions

Nonlinear response of Asian summer monsoon precipitation to emission reductions in South and East Asia

Anthropogenic aerosol impacts on Pacific Coast precipitation in CMIP6 models

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