Unlike greenhouse gases, contrails (line shaped clouds formed by aircraft) are an easily visible human-driven warming of the climate system. The total magnitude of the warming from contrails is highly uncertain, but is approximately equal to the warming from all greenhouse gases emitted from every aircraft since the dawn of flight.
If the weather is right, contrails can spread out to the cover the sky. The uncertainty in this warming effect comes from the difficulty in distinguishing these older contrails from naturally-formed cirrus clouds.
The shutdown in aviation due to the COVID-19 pandemic and new satellite data provide a unique opportunities to measure the warming impact of aviation on the climate. From tracking the impact of individual aircraft to large scale changes in cloud, satellites find large impacts of aviation on clouds and show us which kind of aircraft have particularly large warming impacts on the climate.