Preprints
https://doi.org/10.5194/acp-2021-210
https://doi.org/10.5194/acp-2021-210

  16 Mar 2021

16 Mar 2021

Review status: this preprint is currently under review for the journal ACP.

The Climate Impact of COVID19 Induced Contrail Changes

Andrew Gettelman, Chieh-Chieh Chen, and Charles G. Bardeen Andrew Gettelman et al.
  • National Center for Atmospheric Research, Boulder, CO, USA

Abstract. The COVID19 pandemic caused significant economic disruption in 2020 and severely impacted air traffic. We use a state of the art Earth System Model and ensembles of tightly constrained simulations to evaluate the effect of the reductions in aviation traffic on contrail radiative forcing and climate in 2020. In the absence of any COVID19 pandemic caused reductions, the model simulates a contrail Effective Radiative Forcing (ERF) 62 ± 59 m Wm−2 (2 standard deviations). The contrail ERF has complex spatial and seasonal patterns that combine the offsetting effect of shortwave (solar) cooling and longwave (infrared) heating from contrails and contrail cirrus. Cooling is larger in June–August due to the preponderance of aviation in the N. Hemisphere, while warming occurs throughout the year. The spatial and seasonal forcing variations also map onto surface temperature variations. The net land surface temperature change due to contrails in a normal year is estimated at 0.13 ± 0.04 K (2 standard deviations) with some regions warming as much as 0.7 K. The effect of COVID19 reductions in flight traffic decreased contrails. The unique timing of such reductions, which were maximum in N. Hemisphere spring and summer when the largest contrail cooling occurs, means that cooling due to fewer contrails in boreal spring and fall was offset by warming due to fewer contrails in boreal summer to give no significant annual averaged ERF from contrail changes in 2020. Despite no net significant global ERF, because of the spatial and seasonal timing of contrail ERF, some land regions that would have cooled slightly (minimum −0.2 K) but significantly from contrail changes in 2020. The implications for future climate impacts of contrails are discussed.

Andrew Gettelman et al.

Status: open (until 11 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Andrew Gettelman et al.

Data sets

Simulations of Contrails Under COVID-19 Effects Andrew Gettelman https://zenodo.org/record/4584078

Model code and software

Model Code for Simulations of Contrail COVID-19 Effects Andrew Gettelman https://zenodo.org/record/4584078

Andrew Gettelman et al.

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Short summary
The COVID19 pandemic caused significant economic disruption in 2020 and severely impacted air traffic. We use a climate model to evaluate the effect of the reductions in aviation on climate in 2020. Contrails in general warm the planet, and COVID reductions in contrails cooled the land surface in 2020. The timing of reductions in aviation was important and this may change how we think about future effects of contrails.
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