The Climate Response to Emissions Reductions Due to COVID‐19: Initial Results From CovidMIP

Abstract

Many nations responded to the COVID-19 pandemic by restricting travel and other activities during 2020, resulting in temporarily reduced emissions of CO 2 , other greenhouse gases and ozone and aerosol precursors. We present the initial results from a coordinated Intercomparison, CovidMIP, of Earth system model simulations which assess the impact on climate of these emissions reductions. Twelve models performed multiple initial-condition ensembles to produce over 300 simulations spanning both initial condition and model structural uncertainty. We find model consensus on reduced aerosol amounts (particularly over southern and eastern Asia) and associated increases in surface shortwave radiation levels. However, any impact on near-surface temperature or rainfall during 2020-2024 is extremely small and is not detectable in this initial analysis. Regional analyses on a finer scale, and closer attention to extremes (especially linked to changes in atmospheric composition and air quality) are required to test the impact of COVID-19-related emission reductions on near-term climate. Plain Language Summary Many nations responded to the COVID-19 pandemic by restricting travel and other activities during 2020. This caused a temporary reduction in emissions of CO 2 and other pollutants. We compare results from twelve Earth system models to see if the emissions reductions affected climate. These twelve models performed over 300 experiments using multiple initial-conditions. We find a consensus that aerosol amounts were reduced, especially over southern and eastern Asia, during 2020-2024. This led to increases in solar radiation reaching the surface in this region. However, we could not detect any associated impact on temperature or rainfall. We recommend more analyses on regional scales. We also suggest that analysis of extreme weather and air quality would be useful to test the impact on climate of emission reductions due to COVID-19.

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

“…Evaluating the MACv2-SP approach against the aerosol optical depth from a complex aerosol-climate model indicates similar regional scaling behaviours ( Fiedler et al, 2019b ). Moreover, our MACv2-SP data in CovidMIP models generate results that fall within the spread from aerosol-climate model simulations with more complex aerosol treatments ( Jones et al, 2021 ). A complete technical description of MACv2-SP is given by Stevens et al (2017) .…”

“…We show the anthropogenic aerosol optical properties and the associated effect on clouds from MACv2-SP. The new MACv2-SP data is based on the COVID-19 emission data from Forster et al (2020a) for use in CovidMIP ( Jones et al, 2021 , Lamboll et al, 2021 )). Our results point to a reduction in the global anthropogenic aerosol optical depth by 10% due to the pandemic compared to the baseline.…”

Modifying emissions scenario projections to account for the effects of COVID-19: protocol for CovidMIP

“…It assigns areas of sea to the nearest country. We then check whether the four corners of the pixel are all in the sea using the global_land_mask python module (Karin, 2020). If all four corners are sea, the pixel is instead classified as international waters and is therefore modified by the internationally averaged change in shipping activity rather than the national change in shipping level.…”

Coupled Climate Responses to Recent Australian Wildfire and COVID‐19 Emissions Anomalies Estimated in CESM2

“…In this work, we therefore seek to further explore these issues using the Community Earth System Model version 2 (CESM2; Danabasoglu et al, 2020). We use best estimates of emissions from the Australian wildfires generated from satellite data and use the community-adopted COVID emissions scenario (Lamboll, Jones, et al, 2020) used in Jones et al (2021) to generate simulation ensembles that extend from July 2019 through 2024 using a broad range of initialized states. As these ensembles are large (50 members), they allow for a more precise estimation of forced responses and associated uncertainties than in Jones et al (2021), in one of the best performing climate models available (see Methods).…”

“…We use best estimates of emissions from the Australian wildfires generated from satellite data and use the community-adopted COVID emissions scenario (Lamboll, Jones, et al, 2020) used in Jones et al (2021) to generate simulation ensembles that extend from July 2019 through 2024 using a broad range of initialized states. As these ensembles are large (50 members), they allow for a more precise estimation of forced responses and associated uncertainties than in Jones et al (2021), in one of the best performing climate models available (see Methods). Details of the forcing data sets, climate model, initialization, and analysis methods are given in Section 2, and large-scale aspects of the climate responses are shown and discussed in Section 3.…”