The Climate Response to Emissions Reductions due to COVID-19: Initial Results from Covid Model Intercomparison Project (MIP)

The COVID-19 pandemic led to widespread measures restricting travel, industrial, and commercial activity during 2020. The effects of these changes in socioeconomic activity resulted in temporarily reduced emissions of CO2, other greenhouse gases and ozone and aerosol precursors.

To enable analysis of the effect of reduced emissions on the climate, a set of COVID-19 emission scenarios (CovidMIP) was created spanning the short-term (2020-2024) and possible future economic recovery strategies over the longer-term (2020-2050). All CovidMIP scenarios are based off the SSP2-4.5 scenario as a baseline against which to apply the emissions reductions. Simulations are run from SSP2-4.5 on 1st January 2020 and following the new forcing in line with emissions reductions.

CovidMIP Scenarios:

• ssp245-Base (2020-2050): baseline scenario, based on SSP2-4.5
• ssp245-TwoYearBlip (2020-2024): a strong decrease in emission during 2020, and full recovery back to SSP2-4.5 by 2022. 
• ssp245-cov-strgreen (2020-2050): 2-year Covid-19 emissions blip followed by strong-green stimulus, based on SSP2-4.5. 
• ssp245-cov-modgreen (2020-2050): 2-year Covid-19 emissions blip followed by moderate-green stimulus recovery, based upon ssp245. Based on SSP2-4.5.
• ssp245-cov-fossil (2020-2050): 2-year Covid-19 emissions blip followed by increased emissions due to a fossil-fuel based recovery, based on SSP2-4.5.

All of these scenarios have become part of the CMIP6 set of experiments.

Dr. Paul Nolan, Climate Scientist, ICHEC said, 

“Because any climate signal due to COVID-19-induced emissions reductions is considered likely to be small, it is advantageous to carry out large initial-condition ensembles which have been shown to enable detection of even small regional climate signals. Such large ensembles of climate simulations allow for a robust quantification of projection uncertainty (and detection of robust projected changes); for example, if all ensemble members agree on a particular projection then this projection is assigned a high-level of confidence. Conversely, if there is disagreement between ensemble members for a particular projection, then this projection is assigned an appropriate low level of confidence.”

To this end, a collaboration of international climate modelling institutes was established (led by the UK Met Office) to investigate whether the COVID-19 induced reduction in emissions have any impact on the Earth’s climate [1,2]. The CovidMIP protocol is open to all international institutions participating in CMIP6 and to date, twelve models have provided data for analysis. Climate researchers at ICHEC (funded by EPA, Met Eireann and the Marine Institute), and in collaboration with European partners in the EC-Earth consortium, contributed to the experiment by using the EC-Earth Earth System Climate Model to simulate the effects on reduced emissions of CO2 and other pollutants on the global climate. In total, ICHEC completed an ensemble of EC-Earth simulations, comprising over 400 years, for each of the CovidMIP scenarios. The simulations were run on the ICHEC supercomputer and the resulting large datasets were hosted, and shared with the international research community, on the ICHEC Earth System Grid Federation (ESGF) node. EC-Earth partners, from various European Institutes, also contributed to the experiment.

The results of these initial simulations were analysed by an international team of climate researchers, led by the UK Met Office, and a paper was published in the Journal of Geophysical Research Letters [1,2].  Note that this manuscript focuses on the immediate term impact (from 2020-2024) of the “two-year blip” scenario under which emissions revert to the baseline levels by the end of 2022. The larger global projections dataset under scenarios spanning possible future economic recovery strategies over the longer-term (2020-2050) is currently being analysed by the international research community.

The paper presents the initial results from the coordinated Intercomparison, CovidMIP, of Earth system model simulations which assess the impact on climate of deductions in emissions; “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” [1].

The result of this initial paper shows that the climate impacts of global Covid-19 restrictions is projected to be small over the period 2020-2024.

The datasets are currently being analysed to assess the longer term (2020-2050) implications of COVID-19-related emission reductions and future economic recovery strategies (strong green, moderate green, and fossil fuel dependent). It is expected the choice of recovery strategies will have a stronger impact on the global climate and have profound impacts on our ability to meet long-term climate goals. Multi-model analysis of these simulations will enable clearer understanding of the threats and opportunities arising from the current situation.

This initial study has only begun to scratch the surface of the results becoming available from the CovidMIP simulations. We stress that this work has been the result of a very rapid response of the Earth system modeling community. It often takes several years to design and perform coordinated MIP experiments, and process the data for publication in a community archive. This activity has taken place in only a matter of months. This paper is just the very first analysis of initial results and therefore serves only as a first indication of how the climate system has responded to the perturbations to emissions in response to the COVID‐19 pandemic. It is not possible at this stage to analyze all of the responses, nor the processes responsible for changes across the whole system. But this study sets the scene and informs priorities for future analysis

References

1. Jones, C.D., J.E. Hickman, S.T. Rumbold, J. Walton, R.D. Lamboll, R.B. Skeie, S. Fiedler, P. Forster, J. Rogelj, M. Abe, M. Botzet, K. Calvin, C. Cassou, J.N.S. Cole, P. Davini, M. Deushi, M. Dix, J.C. Fyfe, N.P. Gillett, T. Ilyina, M. Kawamiya, M. Kelley, S. Kharin, T. Koshiro, H. Li, C. Mackallah, W.A. Müller, P. Nabat, T. van Noije, P. Nolan, R. Ohgaito, D. Olivié, N. Oshima, J. Parodi, T.J. Reerink, L. Ren, A. Romanou, R. Séférian, Y. Tang, C. Timmreck, J. Tjiputra, E. Tourigny, K. Tsigaridis, H. Wang, M. Wu, K. Wyser, S. Yang, Y. Yang, and T. Ziehn, 2021: The climate response to emissions reductions due to COVID19: Initial results from CovidMIP. Geophys. Res Lett.,  https://doi.org/10.1029/2020GL091883 
2. Wheeling, K. (2021), Did the drop in COVID-related emissions affect the climate?, Eos, 102, https://doi.org/10.1029/2021EO158007. Published on 04 May 2021. https://eos.org/research-spotlights/did-the-drop-in-covid-related-emissions-affect-the-climate