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

Abstract

Abstract. Lockdowns to avoid the spread of COVID-19 have created an unprecedented reduction in human emissions. While the country-level scale of emissions changes can be estimated in near real time, the more detailed, gridded emissions estimates that are required to run general circulation models (GCMs) of the climate will take longer to collect. In this paper we use recorded and projected country-and-sector activity levels to modify gridded predictions from the MESSAGE-GLOBIOM SSP2-4.5 scenario. We provide updated projections for concentrations of greenhouse gases, emissions fields for aerosols, and precursors and the ozone and optical properties that result from this. The code base to perform similar modifications to other scenarios is also provided. We outline the means by which these results may be used in a model intercomparison project (CovidMIP) to investigate the impact of national lockdown measures on climate, including regional temperature, precipitation, and circulation changes. This includes three strands: an assessment of short-term effects (5-year period) and of longer-term effects (30 years) and an investigation into the separate effects of changes in emissions of greenhouse gases and aerosols. This last strand supports the possible attribution of observed changes in the climate system; hence these simulations will also form part of the Detection and Attribution Model Intercomparison Project (DAMIP).

COVID-19 lockdown NO<sub>x</sub> emission reductions can explain most of the coincident increase in global atmospheric methane

“…Refinements to this simple estimate will need to account for several additional complications. The NOx emission changes have temporal structure (Lamboll et al, 2021), as do the sensitivities of methane to NOx (e.g., Stevenson et al, 2004), and these will interact. In addition, we have ignored any spatial variations in aircraft emissions, but Stevenson and Derwent (2009) found that NOx emissions into cleaner environments had larger effects; there are also likely spatial variations within the large regions we have used for the surface NOx emissions.…”

“…Measurements of nitrogen dioxide (NO2) from satellite instruments and nitrogen monoxide (NO) and NO2 from surface sites show that levels of atmospheric NOx (NO + NO2) dramatically fell globally during 2020 (Bauwens et al, 2020) as COVID-19 lockdowns around the world reduced emissions, mainly from transportation (Venter et al, 2020;Lamboll et al, 2021).…”

“…Discussion started: 3 August 2021 c Author(s) 2021. CC BY 4.0 License.COVID-19 lockdown impacts on NOx emissionsLamboll et al (2021) compiled estimates of the impact of COVID-19 lockdowns on global anthropogenic NOx emissions, as monthly mean time series, with spatial resolution 0.5° latitude by 0.5° longitude. We use these data to calculate the difference in surface NOx emissions between 2019 (pre-lockdown) and 2020 for the four HTAP regions, as well as for the Northern and Southern Hemispheres.…”

“…We use these data to calculate the difference in surface NOx emissions between 2019 (pre-lockdown) and 2020 for the four HTAP regions, as well as for the Northern and Southern Hemispheres. The annual reduction in global surface NOx emissions from 2019 to 2020 was about 19.38 Tg(NO2), or 15% Lamboll et al (2021). also compiled data on aviation emissions, estimating a global reduction of about 0.83 Tg(NO2),…”

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

“…Based on the new emission data, the scientific community plans to investigate the co-occurrence of climate anomalies and the COVID-19 impacts on global air quality. To this end, a new climate model inter-comparision project for 2015-2050 with the revised emission scenarios has been proposed (Covid-MIP, Lamboll et al, 2021) under the umbrella of the Detection and Attribution Model Intercomparison Project (DAMIP, Gillett et al, 2016) endorsed by CMIP6. Nine CMIP6 models in the sixth assessment report of the IPCC (IPCC, 2021) use the simple plumes aerosol parameterization MACv2-SP (Fiedler et al,3 J o u r n a l P r e -p r o o f…”