Global Response of Cirrus Coverage and DTR to the COVID-19 Pandemic

Abstract:

International response to the COVID-19 pandemic led to drastic reductions in economic activity, industry, and emissions around the globe, providing an unprecedented opportunity to investigate the short-term climate impacts of a range of human activities. Aviation has been one of the most dramatically impacted sectors, with global flight traffic reduced by more than 75% in early April.

Previous attempts to determine a relationship between aviation-induced cirrus and diurnal temperature range (DTR) have proved inconclusive, due primarily to the limited spatial and temporal extents of previous flight groundings (e.g. those following the terrorist attacks of Sept 11, 2001, and the eruption of Eyjafjallajökull in 2010). The COVID-19 shutdown, which has persisted for months rather than days, provides a more robust sample with which to investigate these trends.

In this work, we compile MODIS satellite observations, ERA5 reanalyses, GHCN temperature records, and FlightRadar24 aviation data to quantify changes in cirrus and DTR during the COVID-19 pandemic, and relate these to changes in aviation. After removing contributions from long-term trends and transient meteorological events, we find significant reductions in cirrus coverage over Europe and China, accompanied by a corresponding increase in DTR. We further provide evidence that the two are causally linked, and that DTR changes are likely not induced by changes in parameters such as aerosol optical depth.