Mechanisms for a remote response to Asian anthropogenic aerosol in boreal winter

Abstract

Asian emissions of anthropogenic aerosols and their precursors have increased rapidly since 1980, with half of the increase since the pre-industrial era occurring in this period. Transient experiments with the HadGEM3-GC2 coupled model were designed to isolate the impact of Asian anthropogenic aerosols on global climate in boreal winter. It is found that this increase has resulted in local circulation changes, which in turn have driven decreases in precipitation over China, alongside an intensification of the offshore monsoon flow. No large temperature changes are seen over China. Over India, the opposite response is found, with decreasing temperatures and increasing precipitation. The dominant feature of the local circulation changes is an increase in low-level convergence, ascent, and precipitation over the Maritime Continent, which forms part of a tropical Pacificwide La Niña-like response.HadGEM3-GC2 also simulates pronounced far-field responses. A decreased meridional temperature gradient in the North Pacific leads to a positive Pacific-North American circulation pattern, with associated temperature anomalies over the North Pacific and North America. Anomalous northeasterly flow over northeast Europe drives advection of cold air into central and western Europe, causing cooling in this region. An anomalous anticyclonic circulation over the North Atlantic causes drying over western Europe. Using a steadystate primitive equation model, LUMA, we demonstrate that these far-field midlatitude responses arise primarily as a re-sult of Rossby waves generated over China, rather than in the equatorial Pacific.Published by Copernicus Publications on behalf of the European Geosciences Union.

Significant climate impacts of aerosol changes driven by growth in energy use and advances in emission control technology

“…3c to d), but Asia, Europe, and the Arctic deviate significantly from the linear relationship. This supports previous studies demonstrating that regional precipitation responses are not only linked to temperature through regional energy budget constraints but also depend on other factors such as prevailing circulation patterns and remote telecon- nections (Bollasina et al, 2014;Wilcox et al, 2019;Lewinschal et al, 2019). Overall, the above indicates the importance of changes in aerosol-related emissions in both global and regional precipitation changes.…”

“…Overall, anthropogenic aerosols cause a net cooling of the Earth; almost a third of the warming from increases in GHGs is thought to have been counteracted by cooling due to increased anthropogenic aerosols since the 1950s (Stocker et al, 2013). Yet, despite extensive research in the last decade that has led to significant progress in our understanding of the effects of aerosols Ramaswamy, 2009, 2011;Shindell and Faluvegi, 2009;Allen and Sherwood, 2011;Bollasina et al, 2011;Boucher et al, 2013;Hwang et al, 2013;Wilcox et al, 2013;Xie et al, 2013;Shindell, 2014;Wang et al, 2015), there are still major uncertainties associated with their impacts on climate (Carslaw et al, 2013a;Fan et al, 2016;Lee et al, 2016;Fletcher et al, 2018).…”

“…All these uncertainties make it challenging to project future climate and to quantify the associated impacts on a range of sectors. More importantly, despite ongoing debates as to whether aerosol has larger impacts on mean climate and climate extremes compared to GHGs (Feichter et al, 2004;Xie et al, 2013;Wilcox et al, 2019), a large body of studies indicate that, per unit of forcing or warming, aerosols have significantly larger impacts than GHGs on both global mean climate (Hansen et al, 2005;Shindell, 2014;Shindell et al, 2015) and global or regional climate extremes (Perkins, 2015;Xu et al, 2015;Lin et al, 2016;Wang et al, 2016;Samset et al, 2018a;Zhao et al, 2018Zhao et al, , 2019a.…”

Record high solar irradiance in Western Europe during first COVID-19 lockdown largely due to unusual weather

“…Furthermore, given the worldwide impact of COVID-19 lockdown on emissions of anthropogenic aerosols and greenhouse gases 12 , there exists a possibility of a response of the global circulation to the perturbed radiation balance. With the inherent variability of the weather, proving such a response is challenging based on a single spring, yet studies with global models have shown interactions between aerosols, clouds and circulation based on longer time scales [46][47][48][49] . To conclude, if we account for additional aerosol effects, the impact of the reduced anthropogenic aerosols due to the lockdown is potentially larger than our estimate of the instantaneous clear-sky radiative effects of the aerosol removal.…”

A La Niña‐Like Climate Response to South African Biomass Burning Aerosol in CESM Simulations

“…Despite the short atmospheric lifetime of aerosols and their heterogeneous spatial distribution, aerosols can alter both local and remote atmospheric circulation (Lewinschal et al, ; Ramanathan et al, ; Shindell et al, ; Undorf et al, ; Wilcox et al, ). Previous studies show that aerosols are linked to several circulation responses, including meridional shifts of the Intertropical Convergence Zone (ITCZ) (Allen, ; Allen et al, ; Hwang et al, ; Rotstayn et al, ; Westervelt et al, ) and the associated decrease in Sahel rainfall (Biasutti & Giannini, ; Rotstayn & Lohmann, ; Undorf et al, ).…”