Preprints
https://doi.org/10.5194/acp-2022-558
https://doi.org/10.5194/acp-2022-558
 
26 Sep 2022
26 Sep 2022
Status: this preprint is currently under review for the journal ACP.

Hemispheric-wide climate response to regional COVID-19-related aerosol emission reductions: the prominent role of atmospheric circulation adjustments

Nora Lea Sophie Fahrenbach and Massimo Alberto Bollasina Nora Lea Sophie Fahrenbach and Massimo Alberto Bollasina
  • School of GeoSciences, University of Edinburgh, James Hutton Road, Edinburgh, United Kingdom

Abstract. The national and global restrictions in response to the COVID-19 pandemic led to a sudden, albeit temporary, emission reduction of many greenhouse gases (GHGs) and anthropogenic aerosols, whose near-term climate impact was previously found to be negligible when focusing on global- and/or annual-mean scales. Our study aims to investigate the monthly-scale coupled climate and circulation response to regional, COVID-19-related aerosol emission reductions, using the output from ten Earth System Models participating in the Covid Model Intercomparison Project (CovidMIP). We focus on January–February and March–May 2020, which represent the seasons of largest emission changes in sulphate (SO2) and black carbon (BC). During JF, a marked decrease in aerosol emissions over eastern China, the main emission region, results in a lower aerosol burden, leading to an increase in surface downwelling radiation and ensuing surface warming. Regional sea-level pressure and circulation adjustments drive a precipitation increase over the Maritime Continent, embedded in a negative PDO/ENSO-like response over the Pacific, in turn associated with a northwestward displacement and zonal shrinking of the Indo-Pacific Walker cell. Remote climate anomalies across the Northern Hemisphere, including a weakening of the Siberian High and Aleutian Low as well as anomalous temperature patterns in the northern mid-latitudes, arise primarily as a result of stationary Rossby wave trains generated over East Asia. The anomalous climate pattern and driving dynamical mechanism reverse polarity between JF and MAM 2020, which is shown to be consistent with an underlying shift of the dominant region of SO2 emission reduction from eastern China in JF to India in MAM. Our findings highlight the prominent role of large-scale dynamical adjustments in generating a hemispheric-wide aerosol climate imprint even on short time scales, which are largely consistent with longer-term (decadal) trends. Furthermore, our analysis shows the sensitivity of the climate response to the geographical location of the aerosol emission region, even after relatively small, but abrupt, emission changes. Scientific advances in understanding the climate impact of regional aerosol perturbations, especially the rapidly evolving emissions over China and India, are critically needed to reduce current uncertainties in near-future climate projections and to develop scientifically informed hazard mitigation and adaptation policies.

Nora Lea Sophie Fahrenbach and Massimo Alberto Bollasina

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-558', Anonymous Referee #1, 10 Oct 2022
    • AC1: 'Reply on RC1', Nora Fahrenbach, 10 Oct 2022
  • RC2: 'Comment on acp-2022-558', Anonymous Referee #2, 03 Nov 2022

Nora Lea Sophie Fahrenbach and Massimo Alberto Bollasina

Nora Lea Sophie Fahrenbach and Massimo Alberto Bollasina

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Short summary
We studied the monthly-scale climate response to COVID-19 aerosol emission reductions during January–May 2020 using climate models. Our results show global temperature and rainfall anomalies driven by circulation changes. The climate patterns reverse polarity from JF to MAM due to a shift of the main SO2 reduction region from China to India. This real-life example of rapid climate adjustments to abrupt, regional aerosol emission reduction has large implications for future climate projections.
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