Radiative effects of reduced aerosol emissions during the COVID-19 pandemic and the future recovery

Abstract

The pandemic in 2020 caused an abrupt change in the emission of anthropogenic aerosols and their precursors. We estimate the associated change in the aerosol radiative forcing at the top of the atmosphere and the surface. To that end, we perform new simulations with the CMIP6 global climate model EC-Earth3. The simulations use the here newly created data for the anthropogenic aerosol optical properties and an associated effect on clouds from the simple plumes parameterization (MACv2-SP), based on revised SO 2 and NH 3 emission scenarios. Our results highlight the small impact of the pandemic on the global aerosol radiative forcing in 2020 compared to the CMIP6 scenario SSP2-4.5 of the order of +0.04 Wm −2 , which is small compared to the natural year-to-year variability in the radiation budget. Natural variability also limits the ability to detect a meaningful regional difference in the anthropogenic aerosol radiative effects. We identify the best chances to find a significant change in radiation at the surface during cloud-free conditions for regions that were strongly polluted in the past years. The post-pandemic recovery scenarios indicate a spread in the aerosol forcing of −0.68 to −0.38 Wm −2 for 2050 relative to the pre-industrial, which translates to a difference of +0.05 to −0.25 Wm −2 compared to the 2050 baseline from SSP2-4.5. This spread falls within the present-day uncertainty in aerosol radiative forcing and the CMIP6 spread in aerosol forcing at the end of the 21st century. We release the new MACv2-SP data for studies on the climate response to the pandemic and the recovery scenarios. Our 2050 forcing estimates suggest that sustained aerosol emission reductions during the post-pandemic recovery cause a stronger climate response than in 2020, i.e., there is a delayed influence of the pandemic on climate.

Effective Radiative Forcings Due To Anthropogenic Emission Changes Under Covid‐19 and Post‐Pandemic Recovery Scenarios

“…After 2023, the atmospheric aerosol contents under the two green recovery scenarios further decrease relative to the baseline pathway, consistent with Fiedler et al. ( 2021 ). The decreases in AACBs and AAODs are mainly in areas with intense human activities, such as the NH continents and their adjacent oceans, with the maximum annual declines exceeding 10 mg m −2 and 0.1, respectively.…”

“…Under moderate and strong green recoveries, the decrease in aerosol emissions leads to increases of 0.8 and 1.0 W m −2 , respectively, in the global annual mean ERF relative to the baseline case. A previous study expected anthropogenic warming to be the weakest in the strong green recovery scenario, due to a larger reduction in WMGHG emissions (Fiedler et al., 2021 ). However, our results emphasize the dominant role of anthropogenic aerosols in driving climate change through the first half of the 21st century.…”

“…Fiedler et al. ( 2021 ) indicated an aerosol ERF spread of −0.68 to −0.38 W m −2 for 2050 under these post‐pandemic recovery scenarios. Although the post‐pandemic economic recovery scenarios are highly idealized, they provide several possible global emissions trends in the future, which consider the potential impacts of Covid‐19 on government investment from countries toward either the fossil fuel economy or green infrastructure (Andrijevic et al., 2020 ; Gillingham et al., 2020 ).…”

Robust evidence for reversal of the trend in aerosol effective climate forcing

“…However, the satellite retrievals are particularly uncertain in this region, due to the large zenith angles and large cloud cover that both hamper aerosol retrievals. Towards the end of the time series investigated here, there were specific effects due to the COVID-19 pandemic in 2020 (Forster et al, 2020;Gettelman et al, 2021;Fiedler et al, 2021). For this reason, and due to the particularly large fire activity, the end year of the data analysed here was chosen as 2019.…”

Comment on acp-2022-295

“…Towards the end of the time series investigated here, there were specific effects due to the COVID-19 pandemic in 2020 (Forster et al, 2020;Gettelman et al, 2021;Fiedler et al, 2021). For this reason, and due to the particularly large fire activity, the end year of the data analysed here was chosen as 2019.…”